JPH1048372A - Fuel assembly, fuel channel box used therefor, and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] An object of the present invention is to appropriately suppress surplus reactivity in a fuel assembly containing plutonium without mixing a neutron absorbing material or a burnable poison inside the fuel rod. The present invention provides a nuclear reactor fuel assembly, a channel box, and a method of manufacturing the same, which are less likely to bend and swell due to irradiation growth. A member containing a burnable poison is disposed inside a channel box so that the burnable poison does not come into direct contact with reactor water, and a <0001> direction of hexagonal zirconium of a zirconium-based alloy sheet is used. A reactor fuel assembly having an orientation ratio (Fl value) of 0.20 to 0.35 and a difference in Fl value of opposing surfaces of the channel box of 0.025 or less, a channel box for the reactor fuel assembly, Production method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly for a nuclear power plant. The present invention relates to a fuel assembly with reduced bending and swelling due to irradiation, a fuel channel box used for the same, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in a nuclear reactor, a fissile material represented by uranium 235 is sealed in a fuel rod and burned to take out and use the combustion energy. Generally, enriched uranium obtained by enriching natural uranium is used as the nuclear fuel material enclosed in the fuel rod. The enriched uranium is molded and sintered into fuel pellets in the state of uranium dioxide sintering, and used in a fuel cladding tube arranged in a square lattice shape.

On the other hand, in recent years, from the viewpoint of effective utilization of uranium resources, a plutonium thermal plan for recycling plutonium in spent uranium fuel extracted from a light water reactor to a light water reactor again has been advanced. In this method, a MOX fuel assembly in which part or most of the uranium fuel rods in the uranium fuel assembly are replaced by plutonium-enriched mixed oxide (Mixed Oxide) fuel rods is loaded into a light water reactor and used as fuel. Things.

At this time, it is desirable that the characteristics of the MOX fuel body be closer to uranium fuel. Further, the design of uranium fuel is in the direction of higher burnup, and accordingly, the design of MOX fuel is also desired to have higher enrichment, that is, it is desirable to increase the amount of plutonium loaded per unit as much as possible. But M
When the loading ratio of plutonium in the OX fuel assembly is increased, there is a difference in the core characteristics between the uranium core and the uranium core due to the difference in the nuclear characteristics of uranium and plutonium. That is, the thermal neutron absorption cross sections of Pu-239 and Pu-241 which are fissile materials are larger than U-235,
Due to the large neutron resonance absorption of Pu-240, the neutron flux spectrum of the MOX fuel becomes harder than the neutron spectrum of the uranium fuel, and the neutron moderating effect is reduced.

[0005] In a nuclear reactor, the core is designed in advance to have an excess reactivity so that the reactor can be operated for a certain operation period. In order to suppress the surplus reactivity, a design is usually adopted in which a burnable poison (BP) represented by gadolinia is mixed into the fuel rod. Even in a reactor core using MOX, surplus reactivity is suppressed by using a plurality of fuel rods in which burnable poison is mixed into the fuel itself. In general, the neutron absorption cross section is
Has 1 / v dependence on neutron energy,
Neutrons with lower energy tend to be better absorbed. For this reason, the neutron absorption of the burnable poison increases as the neutron energy spectrum is softer, that is, the system with more thermal neutrons. Therefore, the reactivity suppression effect of the burnable poison is small in the reactor core using MOX, and in order to obtain the same reactivity suppression effect as that of the uranium core, the use of the fuel rod mixed with the burnable poison is required. The number must be increased. To cope with this, adoption of a technique disclosed in Japanese Patent Application Laid-Open No. 60-146185 is considered. This is because, inside the fuel assembly, attention is paid to the fact that the outer periphery of the fuel assembly near the water gap has a large amount of thermal neutrons, and the neutron spectrum is soft. The purpose is to increase the value of the fuel, reduce the number of gadolinia used, increase the plutonium inventory of the fuel assembly, and reduce the type of pellets used.

However, this method cannot completely eliminate the burnable poisons present in the fuel inside the fuel assembly, and is insufficient from the viewpoint of reducing the plutonium inventory. Was.

To cope with the above problem, a technique disclosed in JP-A-59-72087 has been considered. This technology removes the need for adding burnable poisons to fuel pellets or adjusting uranium enrichment by detachably attaching a reactivity control member to the outer periphery of the fuel channel box of the fuel assembly. It is. In this case, the reactivity control member is composed of a neutron absorbing material such as non-rusting steel and zirconium alloy, and a burnable poison such as gadolinium, silver, indium, boron, cadmium and hafnium dispersed in the non-rusting steel as a single substance or a compound. Or, as it is, coated with non-rusting steel, reflection material such as beryllium coated with non-rusting steel, neutron poison, reflection material, natural and depleted uranium etc. are sandwiched between non-rusting steel and rolled Co-ext
The one that has been subjected to rusion processing is used.

In order to solve the above problem, Japanese Patent Application Laid-Open No. 6-34209
The technology shown in No. 1 has been proposed. In this technique, a moderator rod arranged at the center of a channel box is a double pipe of an outer pipe and an inner pipe, and a combustible poison is filled between the inner and outer pipes.

On the other hand, zirconium alloy is used for a reactor fuel assembly member because it is a material having excellent corrosion resistance and a small neutron absorption cross section. Zr-Sn-Fe called Zircaloy-2 or Zircaloy-4 is used for the above-mentioned applications.
-A Cr-Ni alloy is mainly used. When these alloys are used for a long time in a nuclear reactor, the (0001) plane is oriented in the plate thickness direction, so that elongation and bending deformation in a specific direction and bulging deformation due to irradiation and thermal creep occur. If the fuel channel box is bent or bulged, the operation of the reactor is hindered because the gap for driving the control rod is closed. When bending deformation occurs, the interval between the fuel and the cladding tube changes, and the ratio of water to uranium locally increases or decreases, so that the fission reactivity changes. As a result, corrosion of the fuel cladding tube may be accelerated due to abnormal heat generation, and the fuel may be damaged. In order to prevent the fuel channel box from bending and deforming due to such non-uniformity of neutron irradiation, it has been studied to make the neutron irradiation uniform by changing the fuel assembly loading position in the core.
The bending deformation cannot be prevented, and the reduction of the control rod driving gap and the change in fission reactivity due to the bending deformation are the main factors that limit the life of the fuel channel box.

Japanese Patent Application Laid-Open Nos. 59-229475, 62-200286, 5-17837 and 5-80170 disclose a method of preventing the bending of the fuel channel box by randomly setting the crystal grain orientation. Is disclosed. However, in that case, there is a drawback such as an increase in the amount of bulging deformation due to creep deformation, and it cannot be a complete bending deformation suppressing technique.

In addition, when the channel box expands and deforms particularly in the region near the lower tie plate, the amount of cooling water (bypass flow rate) flowing out of the fuel assembly from the gap between the lower tie plate and the channel box increases. As a result, the flow rate of the cooling water (flow rate in the channel) that contributes to the cooling of the fuel rods decreases, so that the thermal margin of the fuel rods decreases. Conversely, when the bypass flow rate is small, excessive steam voids (bubbles) are generated in the bypass region, and there is a possibility that the control rods and the core measurement device cannot be appropriately cooled. Since the bypass flow rate depends on the size of the gap between the lower tie plate and the channel box, it is not preferable that the amount of creep deformation of the channel box excessively increase during the operation cycle. As a method of reducing the temporal change of the bypass flow rate, a method of increasing the thickness of the channel box on the side where the lower tie plate is mounted, of the end in the longitudinal direction of the channel box, or α + β quenching only in the region near the lower tie plate. However, a method of increasing the degree of crystal orientation has been proposed.

However, no method has been proposed for simultaneously reducing the bending deformation and creep deformation of the channel box.

[0013]

According to the technique disclosed in Japanese Patent Application Laid-Open No. 59-72087, a gap is formed between the channel box and the reactivity control member, so that crevice corrosion and galvanic corrosion are likely to occur. Further, since the reactivity control member comes into direct contact with the reactor water, corrosion of the reactivity control member itself becomes a problem.

Further, as described above, the reactor fuel includes:
Burnable poison is mixed in to suppress the initial excess reactivity. Comparing the dependence of uranium and plutonium absorption cross sections on neutron energy, plutonium has more neutron absorption. For this reason, when plutonium is used in a light water reactor, the amount of thermal neutrons absorbed by reactivity control substances such as control rod materials and burnable poisons decreases, and MOX
In the core loaded with the fuel assembly, the control rod value and the reactivity value of the burnable poison are reduced. Therefore, in the core loaded with the MOX fuel assembly, the number of fuel rods containing the burnable poison to be used is increased. Had to be done.

[0015] This means that the plutonium inventory per fuel assembly decreases, resulting in an increase in the number of fuel assemblies manufactured to consume the same amount of plutonium. This leads to an increase in fuel production costs and fuel transportation costs.

Further, in order to maintain the soundness of the reactor fuel, it is necessary to design the local peaking coefficient so as to maintain an appropriate value over the life of the fuel and to observe the thermal operation limit value. In general, for boiling water reactor fuel,
At the outer peripheral portion of the fuel assembly, that is, near the water gap, the thermal neutron flux tends to be relatively high, and the output of the fuel rods at the outer peripheral portion tends to be high. Therefore, in order to keep the local peaking coefficient of the fuel rods disposed on the outer periphery of the fuel assembly low, it is necessary to increase the enrichment and enrichment types of the pellets and design them. The technique disclosed in Japanese Patent Application Laid-Open No. Hei 6-342091 is not sufficient for solving the above-mentioned problem because the burnable poison is disposed in the center of the channel box.

In the production of MOX fuel, cleaning of the glove box at the time of changing the plutonium enrichment in order to carry out the molding of the fuel pellets in a completely sealed container involves the following steps.
It takes more time than in the case of uranium, and the reduction in the operating rate during production is large. Therefore, if the enrichment type increases, the number of times of cleanup increases, leading to an increase in fuel molding processing cost.

In the prior art for suppressing the bending deformation of the fuel channel box, the crystal orientation of the zirconium alloy member is made random. However, the channel box has a square cylindrical shape. Id 5-801
In Japanese Patent Application Publication No. 70-104, the crystal orientation is randomized by a heat treatment of heating and quenching in the β temperature range, but it is difficult to heat and maintain the whole at a uniform temperature. Therefore, unless the whole is heated and held at a uniform temperature, there is a difference in deformation due to neutron irradiation. The difference in the deformation causes bending. In addition, bulging deformation due to irradiation and thermal creep deformation cannot be suppressed.

The present invention has been made in view of such a problem, and an object thereof is to provide a neutron absorbing material inside a fuel rod in a fuel assembly (MOX fuel assembly) mixed with plutonium. Alternatively, the excess reactivity can be appropriately suppressed without mixing the burnable poison, and at the same time, the bending deformation due to the irradiation growth described above is extremely reduced, and the bulging deformation due to irradiation and thermal creep is reduced. And a method of manufacturing the same.

[0020]

According to the present invention, there is provided a fuel assembly capable of appropriately suppressing surplus reactivity, comprising a fuel rod bundle in which a plurality of nuclear fuel rods containing uranium or plutonium are arranged, A channel box surrounding the rod bundle and a water rod, at least one of which is provided with a burnable poison and is buried so that the burnable poison does not directly contact the reactor water, or the burnable poison is provided. Is preferably coated with a corrosion-resistant metal such as Zircaloy so as not to come into direct contact with reactor water.

As a specific embodiment of the present invention, the burnable poison of the channel box and the water rod is:
Metals, alloys, intermetallic compounds or ceramics, wherein the metal, alloy, intermetallic compound or ceramic is cadmium, samarium, boron, gadolinium,
It is preferable to contain at least one of silver, indium and hafnium.

The burnable poison may be at least one of cadmium, samarium, boron, gadolinium, silver, indium, and hafnium added to zirconium or a zirconium-based alloy as an alloying element. It is preferably made of a metal, alloy, intermetallic compound or ceramics dispersed as at least one of oxide, hydride, and nitride or dissolved in a supersaturated state.

Further, the configuration of the burnable poison in the channel box of the fuel assembly according to the present invention is such that the burnable poison is unevenly arranged in a cross section of the channel box viewed from the longitudinal direction, and the vicinity of the corner. Are deployed in many places, and
Preferably, the burnable poisons are arranged symmetrically and unevenly arranged in the longitudinal direction of the channel box, and more and less at the lower part in the longitudinal direction.

The above-described channel box for a fuel assembly according to the present invention is made of a large zirconium alloy sheet made of hexagonal Z.
The <0001> crystal orientation of the r metal is randomized, the same randomization is achieved at any position of the alloy plate, and the sub-grain boundaries in the grains of the β phase Zr are removed. And Sn5% by weight or less and / or Nb5
% Zirconium-based alloy plate having a Zr of 90% by weight or more and a width of 100 mm or more and a long zirconium-based alloy plate, the <0001> crystal orientation of the hexagonal Zr of the alloy in the longitudinal direction (Fl Value) is 0.20 to 0.35, and preferably, the difference (ΔFl) of Fl between the center and the end is 0.0.
25 or less. In particular, the hexagonal Zr of the alloy
Of the <0001> crystal orientation in the direction perpendicular to the surface of the tubular member (Fr value), the longitudinal orientation (Fl) of the tubular member, and the orientation ratio (Ft) in the plate width direction. 0.20 to 0.35, and the difference in Fl between the opposing surfaces is 0.02.
A value of 5 or less is preferred. Preferably, the alloy has a β phase, a crystal grain size of 50 to 500 μm, and the orientation ratio of the crystal orientation at the center and the end of the plate width is substantially the same. Furthermore, the <0001> crystal orientation of the hexagonal Zr of the alloy is substantially random, and
The amount of bending of the member due to neutron irradiation of Wd / t is 2.
It is preferably 16 mm or less.

The present invention comprises a fuel channel box consisting of a rectangular tubular member welded and connected using two U-shaped zirconium-based alloy members, and an oxide film formed by autoclave treatment on all surfaces. Is preferred.

According to the present invention, there is provided a fuel rod containing a fuel pellet in a fuel cladding tube, a channel box for accommodating a plurality of the fuel rods, a spacer for separating the fuel rods in the channel box, an upper portion of the channel box, In a fuel assembly including an upper lattice plate and a lower lattice plate provided at a lower portion, the channel box is made of a zirconium-based alloy plate having the above-mentioned burnable poison, and has a <0001> crystal orientation of hexagonal Zr of the alloy. Is characterized in that the orientation ratio (Fl value) in the longitudinal direction is 0.20 to 0.35, and the difference of Fl on the opposing surface is preferably 0.025 or less.

The deformation of the zirconium alloy member is hexagonal Zr
This occurs because the <0001> crystal orientation is substantially perpendicular to the member surface. Upon receiving neutron irradiation, the hexagonal lattice shrinks in the <0001> direction and expands in a direction perpendicular to the <0001> direction. Strictly speaking, dislocation planes are introduced in the <0001> direction by neutron irradiation, and contraction and expansion in the specific direction occur. The closer to the center of the core, the higher the neutron irradiation dose, and lower around the core. The channel box arranged in the periphery of the core where the neutron irradiation amount changes rapidly causes a difference in irradiation growth (difference in elongation) between the surface on the center side of the core and the surface opposite to the surface, and thus bends. K is a constant, and L1 and L2 are the elongation due to irradiation growth of the surface on the center side of the core of the conventional material and the surface facing the surface, Fl
Is the orientation probability of the crystal orientation in the longitudinal direction of the channel box,
Assuming that ΔFl is the difference between the Fl values between the facing surfaces, δ (bending amount) = K · {(1-3Fl) (L1-L2) +3
LlΔFl}. It can be seen from this that since L1 and L2 depend on the burnup, when the burnup is constant, the amount of bending of the channel box depends on the Fl value and ΔFl. When the dependency on the Fl value and ΔFl of the bending amount of the channel box in the case of the burnup 35 is calculated using an equation, as shown in FIG. 29 described later, the bending amount is Fl =
It can be seen that the minimum value is obtained between 0.33 and 0.35, and the smaller the value of ΔFl becomes. Here, in practice, considering the allowable amount of bending deformation of the channel box in consideration of the amount of bulging deformation due to creep, at a burnup of 35 GWd / t,
Each must have δ <2.16 mm. Therefore, in this case, ΔFl and Fl values are respectively set to ΔFl ≦ 0.02.
5, Fl = 0.20 to 0.35. Further, when a pressure difference is generated between the inner and outer surfaces of the channel box and the outer wall is deformed to bulge outward, the bulge increases due to creep during irradiation.

It is considered that the β-quenched material has a large number of sub-grain boundaries in the grains and is liable to cause grain boundary slip. Therefore, it can be improved by removing sub-grain boundaries in grains by annealing and recrystallizing after cold rolling.
It is possible to obtain a channel box and a fuel assembly in which the bending of the channel box due to the irradiation growth is reduced and the leakage flow rate is reduced.

The bending deformation occurs because the <0001> crystal orientation of the hexagonal Zr metal is oriented perpendicular to the surface of the zirconium alloy. <000 to suppress irradiation growth
1) Randomization of crystal orientation is effective. Irradiation growth
Since the deformation does not involve a change in volume, even if individual crystal grains of the polycrystal are deformed in a specific direction, the direction is random, so that it is equivalent to not being deformed as a whole.

In order to quantitatively evaluate the orientation of the crystal orientation, the X-ray of a specific crystal plane is usually determined by a combination of reflection and transmission X-ray diffraction methods.
X-ray diffraction intensity was measured, and from the measured X-ray diffraction intensity,
Is generally used to calculate the F-number.

[0031]

(Equation 1)

In equation (1), φ represents a specific direction (for example,
Specific crystal orientation (for example, <000
2> crystal orientation), and V (φ) is the volume fraction of the crystal oriented in the φ direction. The r-direction, t-direction, and l-direction are defined as normal directions (F
r), the longitudinal direction (Fl) of the plate (tube), and the plate width (pipe circumference) direction (Ft) are defined by the following equation: Fr + Ft + Fl = 1.0, and if the crystal orientation is completely randomized, Fr = Ft = Fl = 1/3.

Each of Fr, Ft and Fl is 0.20 to
0.50, Fr 0.25 to 0.5
It is preferable to set it to 0.2, Fl 0.20 to 0.35, Ft 0.25 to 0.36, and particularly to 0.31 to 0.35.

(000) of plates and tubes manufactured according to the normal cold working and repeated annealing process.
2) The Fr value of the crystal plane (equivalent to the (0001) plane) is around 0.7, and the <0001> crystal orientation is mainly oriented in the surface normal direction of the plate (tube). Such a state in which the <0001> crystal orientation is oriented in the surface normal direction is called texture. As shown in FIG. 26 described later, as can be seen from the relationship between the neutron irradiation dose and the irradiation elongation, when the Fl value is 0.23 or more, preferably 0.25 or more, the irradiation elongation is significantly reduced,
It can be seen that by setting the Fl value to 0.30 to 0.35, the elongation becomes substantially 0 (zero) even in a high irradiation range of neutron irradiation quantity ≧ 10 ²² (n / cm ² ).

As a means for obtaining a texture having an Fl value of 0.20 to 0.35, a zirconium alloy member is heated to a β-phase temperature range (a temperature exceeding 980 ° C. for a zircaloy alloy), and βZr crystal grains are removed. In this method, after sufficient growth, cooling is performed, particularly rapid cooling by water spraying, but it is necessary to heat the entire member to a uniform temperature. By performing this treatment, the hexagonal αZr crystal is transformed into a cubic βZr crystal,
During the cooling process, it is transformed again into a hexagonal αZr crystal. In this heat treatment, in order to obtain a texture having an Fl value of 0.20 to 0.35, it is preferable that the βZr crystal grains grow to at least 100 μm or more, and to obtain a texture having an Fl value of 0.20 or more. βZr crystal grains are at least 50 μm or more and 500 μm or less, preferably 150 μm or more and 300 μm
It is as follows. The heating time at the β-phase temperature can be reduced in a shorter time as it is higher in the β-phase temperature range (preferably 1100 to 1350 ° C, more preferably 1100 to 1200 ° C). The holding time at the maximum heating temperature can be performed in a very short time, for example, 1.5 seconds to 100 seconds, preferably 5 seconds.
~ 60 seconds. In particular, it is preferable to perform the process in the range indicated by the mark in FIG.

In order to uniformly heat the entire member, a plate material is used, and the width of the heating body is 3 cm or more, preferably 4.5 cm or more, and more preferably 4.5 to 10 cm (2 turns as a high frequency induction heating coil. The heating can be performed by holding and heating with a roller so as to always keep the gap between the heated body and the heated body constant, performing a plurality of quenching treatments, measuring the temperature of the heated section, and the like. The gap is preferably 1 to 5 mm, particularly preferably 2 to 3 mm.

If the heating temperature is insufficient or the holding time is insufficient even when heating is performed in the β phase temperature range, the desired texture cannot be obtained for the entire member. In order to obtain a texture having a random crystal orientation, βZ having various crystal orientations is required.
It is necessary that the r crystal grains grow sufficiently, and for that purpose, a temperature or holding time (P value of 0.8 or more) is sufficient for βZr crystal grains to grow to at least 50 μm or more.
It is better to

As described above, the Fl value changes depending on the heat treatment, but the temperature and the holding time are important factors. Therefore, in order to make the Fl value 0.50 or less in the β-phase temperature region, it is preferable that the parameter P obtained by the above equation be 1.5 or more (βZr crystal grains 60 μm or more). In particular, the parameter P is between 2.5 and 5
(ΒZr crystal grains 70 to 500 μm), more preferably 3.2 to 5 (βZr crystal grains 100 to 500 μm).

In the method of manufacturing the channel box of the fuel assembly according to the present invention, a dent is formed in one zirconium-based alloy material plate of the channel box, and a plate of a burnable poison is engaged in the dent. Arranged, and the other zirconium-based alloy material plate of the channel box is joined so that the burnable poison is embedded in the two material plates, and the joined portion is not subjected to electron beam welding or welding. Hot rolling or hot pressing, and thereafter, cold rolling and annealing are repeated as appropriate times, as another aspect of the manufacturing method, a plate of a combustible poison between the two material plates of the channel box The three plates are interposed, hot-rolled and pressed, and the ends are cold-rolled and annealed as appropriate without electron beam welding or welding in vacuum. Then, while continuously moving the long zirconium-based alloy plate in which the burnable poison is engaged and arranged, β
Heat to single phase temperature range and cool. At that time, the alloy was heated and maintained in the β-phase single-phase temperature region so that the orientation ratio (Fl value) of the <0001> crystal orientation of the hexagonal Zr of the alloy to the plate longitudinal direction became 0.20 to 0.35. In addition, the difference in heating temperature between the center and the end in the plate width direction is reduced. At this time, heating in the β-phase temperature region is controlled by a parameter P obtained by the following equation.
It is preferable to rapidly cool after holding for a short time so that the value of is 0.8 or more.

P = (3.55 + logt) × log (T−980) (t: heating time (second), T: heating temperature (° C.)) Heating in the β-phase temperature region is induced by moving the plate material. The coil is continuously heated for a desired holding time and simultaneously cooled forcibly after the heating.The heating to the β phase makes the <0001> orientation random and has high corrosion resistance to high-temperature, high-pressure pure water. Is obtained. Cooling is preferably performed by a fountain (preferably hot water injection), and is 50 to 300 ° C./sec, preferably 100 ° C./sec.
It is preferable to set the cooling rate to ２５０250 ° C./sec or more. Infrared and electric furnaces can be used as the heating means.

In particular, it is preferable to use hot water having a temperature equal to or higher than room temperature as the cooling medium to reduce the cooling rate by cooling to prevent deformation due to cooling. The temperature is preferably from 40 to 80C.

After the β quenching treatment, cold rolling is performed and annealing is performed to recrystallize the crystal. By removing sub-grain boundaries in the β phase crystal grains, grain boundary slip is prevented from occurring, and the channel box is formed. The swelling deformation due to the creep deformation due to the differential pressure generated on the inner and outer surfaces can be suppressed.

Thereafter, the Zircaloy plate material with the combustible poison engaged is bent and welded to form a square tube. Next, annealing for uniformly heating the whole is performed. Annealing 500-6
It is carried out at 50C (preferably 550-640C). It is preferable that the annealing is performed by constraining by a constraining member such as austenitic stainless steel having a larger coefficient of thermal expansion than the Zr-based alloy, whereby the tubular member can be shaped. These heat treatments are performed in a non-oxidizing range atmosphere, particularly preferably in Ar.

After the final heat treatment, the oxide film on the surface is removed by sandblasting and pickling. After the oxide film is removed, the surface is oxidized by an autoclave, and a stable oxide film is formed on the surface to obtain a final product. In addition, the ends such as the screw holes for fixing at the both ends described above are used after being removed.

The fuel assembly of the present invention configured as described above is included in the fuel by disposing a neutron absorber or a burnable poison in the fuel channel box of the fuel assembly used for the boiling water reactor. The gadolinia amount can be reduced or eliminated, and the local peaking coefficient of the fuel assembly can be reduced.

A BP member, which is a neutron absorber or a burnable poison, is provided in the channel box. In particular, the use of Gd ₂ O ₃ as the BP member suppresses the reactivity and reduces the local peaking coefficient. It will be described below.

The change of the control value with the neutron irradiation amount is as shown in FIG. 33. Therefore, the initial surplus reactivity is suppressed, that is, in the first cycle (irradiation amount: up to 1.0 × 10 ^22).
nvt) can be controlled by using Gd ₂ O ₃
Is optimal. Further, in the fuel assembly, the amount of thermal neutrons is larger in the water gap portion than in the inside of the assembly, and the neutron spectrum is softer.
This is attributable to two factors: the outer peripheral portion has a relatively larger amount of water than the inside of the fuel assembly, and thermal neutron absorption by the fission material inside the fuel assembly.

On the other hand, the burnable poison and the neutron absorbing material are shown in FIG.
The neutron absorption cross section of 1 / v dependence shown in FIG. 4 has a larger reactivity, and the more thermal neutrons, the greater the reactivity suppression effect. In MOX fuel, neutron absorption by plutonium is greater than that of uranium, so the neutron spectrum inside the fuel assembly is even harder, and the effect of suppressing the reactivity of burnable poisons is reduced. Therefore, the reactivity suppression effect can be increased by disposing the burnable poison in the water gap portion, that is, inside the channel box, rather than mixing the burnable poison into the fuel.

Further, looking at the distribution of the thermal neutrons in the fuel assembly, as shown in FIG. 35, the thermal neutrons are raised at the outer peripheral portion of the fuel assembly having a relatively large amount of water. The neutron flux is low at the center of. Therefore, the local peaking coefficient also tends to be higher at the outer periphery of the fuel assembly. By mixing a burnable poison or a neutron absorbing material into the fuel channel box near the region where the local peaking coefficient is high, the local peaking coefficient at the outer periphery of the fuel assembly can be effectively suppressed.

The function of distributing burnable poisons and neutron absorbers in the longitudinal direction of the channel box is as follows.

In the boiling water reactor, since the cooling water flows from the lower part to the upper part of the reactor core while boiling inside the reactor core, steam bubbles (voids) are distributed in the axial direction of the reactor core. In addition, the amount of the voids tends to increase toward the upper part of the core. In a light water moderator, the moderator (water) density controls the fission reaction, and the fission reaction is designed to be promoted as the moderator density increases. Therefore, when considering the power distribution in the axial direction of the core, the power tends to be higher in the lower part of the core with less voids than in the upper part of the core with many voids. To deal with this, the amount of neutron absorbers and burnable poisons present in the channel box is distributed in such a way that the amount is larger in the lower region where the reactivity is large in the axial direction, and becomes smaller toward the upper region. Will be able to deal with it.

Further, since the neutron spectrum is hard in the upper region in the axial direction due to the high void fraction, the loss of burnable poisons and neutron absorbing materials tends to be slower than that in the lower region. By distributing the poison and the neutron absorbing material in the axial direction, the loss in the axial direction proceeds evenly.

Further, in the present invention, the burnable poison is buried in the channel box, or the burnable poison is coated with a metal such as Zircaloy.
Since the burnable poison does not come into direct contact with the reactor water, corrosion of the burnable poison itself, crevice corrosion between the channel box and the burnable poison, and galvanic corrosion do not occur.

Further, according to the present invention, since the burnable poison is buried inside the blank in the state of the blank in the manufacturing process before forming the channel box, the burnable poison is not exposed to the outside. By adopting the channel box manufacturing method of the present invention, a low-irradiation deformed channel box in which a burnable poison is buried can be easily manufactured, and separation between the material plates of the channel box can be easily achieved. And other phenomena can be eliminated.

[0055]

(Embodiment 1) FIG. 1 shows a first embodiment of a fuel assembly A of the present invention. The upper part of FIGS. 1 (a) and 1 (b) is A cross-sectional view as viewed from the longitudinal direction of the channel box, and a lower view is a side view as viewed from the longitudinal direction of the channel box. The fuel assembly A includes a channel box 1, a bundle of a large number of fuel rods 2, a water rod 3, and a BP containing a combustible neutron absorbing poison (BP) disposed in four surrounding members of the channel box 1. It is formed from the member 4 and the like. The BP member 4 is disposed so as to be buried in the longitudinal direction in the vicinity of a corner of the four surrounding side surfaces of the channel box 1. FIG. 1A shows two water rods 3, FIG. 1B shows one water rod 3, and FIGS. 1A and 1B show the same embodiment. FIG.
Is a second embodiment, in which a BP member 4 is buried and arranged in a longitudinal direction of a corner portion on a side surface of the channel box 1.

By burying and disposing the BP member 4 in the channel box 1 as described above, since the BP member 4 does not come into direct contact with the reactor water, crevice corrosion, galvanic corrosion and the like can be prevented.

Further, the BP member 4 is connected to the channel box 1
By arranging them at the corners and near corners, the local peaking coefficient at the corners of the fuel assembly A can be effectively suppressed.

FIGS. 3 to 5 show a method of manufacturing the channel box 1 of the fuel assembly A of the first embodiment. First, as shown in FIG. 3, a dent having a depth of about 0.2 mm to 1.5 mm is formed in a Zircaloy material plate serving as a channel box 1 in the longitudinal direction of the plate. The depth of the dent is determined by the content of the BP metal and the width of the BP member. Then, in the dent, B of the same size as the dent
The P member 4 is fitted, another thin Zircaloy material plate is bonded, and the joint is subjected to electron beam welding in a vacuum as needed. Thereafter, hot rolling, cold rolling, and annealing (annealing) are performed several times at 600 to 700 degrees to complete a single sheet. Instead of hot rolling, the material may be
There is also a method of heating to 20 degrees and rolling by a hot press to make a single plate. Also, if there is no separation between the material plates,
Electron beam welding can also be omitted, and particularly when rolling by hot pressing, there is a high possibility that the electron beam welding is omitted. After the single plate is formed, the plate is heated and maintained in a β phase temperature range for the purpose of randomizing the crystal orientation of hexagonal zirconium of the zirconium-based alloy, and then rapidly cooled. A specific method of the β quenching is performed by heating with a high frequency induction coil and cooling with a water cooling nozzle provided below the coil. The coil and the water-cooling nozzle are fixed, and are performed while continuously moving the plate material downward. The heating temperature was measured by using an optical pyrometer directly on the plate in the space immediately before the water cooling nozzle immediately after the plate was heated. The heating and holding time is performed by adjusting the moving speed of the plate material. In this example, the temperature difference between the end portion and the center portion of the plate material was 10 ° C. or less, and the heating temperature was set at 1050 to 1150 ° C. and the holding time was set to several combinations of 3 to 20 seconds. As cooling water, warm water of 40 to 80 ° C. was used, and one cooling was performed using a substantially constant temperature of warm water. FIG. 6 is a perspective view of a quenching device for a zirconium-based alloy plate material in which a burnable poison is engaged and arranged according to the present invention. The zirconium-based alloy plate 41 in which the burnable poison is engaged is provided with rollers at the upper part of the high-frequency induction heating coil 44 and at the lower part of the cooling water spray nozzle 46 so that the plate 41 does not move back and forth and right and left. The gap between the plate 44 and the plate member 41 is continuously moved as indicated by an arrow so that the gap is always constant during heating and cooling. When the plate material 41 passes through the coil from above to below at a constant speed, the entire heat treatment is completed. Heating temperature is 11
The feed speed of the plate material 41 and the output of the high-frequency power supply 5 were adjusted so that the holding time at 00 ° C. was 10 seconds.

Since a large number of layered or needle-shaped sub-grain boundaries are present in the βZr crystal grains and grain boundary slip is likely to occur, the creep is caused by the differential pressure generated on the inner and outer surfaces of the channel box during irradiation. Bulging deformation increases. Therefore, in order to remove sub-grain boundaries in grains by recrystallization, after β-quenching, cold rolling is performed at 600 ° C. to 700 ° C. for about 2 hours.
Time annealing is performed.

Thereafter, in order to obtain the shape of the channel box 1, cold bending is performed in a U-shape as shown in FIG. 4 to form a square cylindrical body by plasma welding, and by crushing and cutting the weld bead. Flattening, Inserting a SUS304 cross-shaped mandrel into the cylinder, shaping annealing and straightening by heating at 600 ° C for 2 hours, sand blasting of the oxide scale formed by the aforementioned quenching, and removal of the inner and outer surfaces by pickling. , Surface finishing such as degreasing, and autoclave treatment with water vapor are applied to the final product. FIG. 7 is a partial cross-sectional view of a BWR fuel assembly using the rectangular tube manufactured as described above.

The BWR fuel assembly, as shown in FIG.
A large number of fuel rods 11 and spacers 12 for holding them at a predetermined interval from each other, a rectangular channel box 1 for accommodating them, an upper part for holding both ends of fuel rods 11 containing fuel pellets in a fuel cladding tube. It comprises a tie plate 14, a lower tie plate 15, and a handle 13 for transporting the whole.

(Embodiment 2) As shown in FIG.
Plate material 4 sandwiched between Zircaloy material plates 41 is 600
There is a method in which hot rolling is performed at about 700 ° C., pressure bonding is performed, and both ends are electron-beam welded in a vacuum, and then cold rolling and annealing are repeated to form a single plate. Also in this case, if there is no problem such as separation of the material plate 41, electron beam welding in a vacuum can be omitted. The BP member 4 is completely covered with the Zircaloy material 41 as shown in the figure, and does not contact the outside. In the subsequent manufacturing steps, the channel box is manufactured through steps similar to those shown in FIGS.

(Embodiment 3) FIG. 8 shows a third embodiment, in which a BP member 4 is fitted in a recess of a channel box 1 and the outside is covered with a thin plate 5 made of a Zircaloy material (Zry). In the same manner as in the first embodiment, β quenching is performed. A dent is formed in the outer corner portion and the vicinity of the corner portion of the channel box 1 and the BP member 4 is fitted therein. Then, a part of the side surface or the entire side surface of the channel box 1 is covered with a thin plate 5 made of Zry and welded. In this case, the BP member 4 is not directly brought into contact with the reactor water.

FIG. 8A shows a case where the BP member 4 is arranged at a corner of the channel box 1 and only the outside of the BP member is covered with a thin plate 5, and FIG.
This is a case where the entire area around the channel box 1 is covered with the thin plate 5.

FIGS. 9A and 9B show a fourth embodiment, in which the BP member 4 is arranged in the vicinity of the corner, and the rest is the same as the embodiment of FIG.

When the BP member 4 coated with another metal as described later is used, it is not necessary to cover with a Zry thin plate.

(Embodiment 4) FIG. 10 shows the shape of the BP member 4, and FIG. 10A shows that the width of the BP member 4 at the lower part in the longitudinal direction of the channel box is discontinuous compared to the upper part. FIG. 10B shows a case where the width of the BP member 4 at the lower part in the longitudinal direction of the channel box 1 is continuously increased as compared with the upper part, and β quenching is performed in the same manner as described above. .

FIG. 11 shows a case where the BP member 4 is divided in the longitudinal direction of the channel box 1. In this case, the BP members 4 having the same length are arranged at regular intervals, and the BP member 4 having a longer length as shown in FIG.
There are cases where the members 4 are arranged with a reduced interval. here,
Considering the power distribution in the core axis direction, since steam bubbles (voids) exist in the core axis direction of the nuclear reactor and increase toward the upper part of the core, the power distribution in the core axis direction is represented by the curve in FIG. The lower part of the core having less voids as shown in a is larger than the upper part of the core having many voids. So, as mentioned above,
By disposing the amount of the BP member 4 in the upper portion and increasing the amount in the lower portion, the power distribution in the core axis direction can be flattened as shown by a curve b.

FIG. 13 shows a case where the width of the BP member 4 in the longitudinal direction of the channel box 1 is made uniform. FIG.
Is a case where the length of the BP member 4 in the longitudinal direction of the channel box 1 is set to 80 to 100% of the effective length of the fuel rod 2.

(Embodiment 5) FIGS. 14 to 16 show a method of manufacturing the BP member 4, which is not shown, but performs β quenching similarly. The BP member 4 contains at least one of cadmium (Cd), samarium (Sm), boron (B), gadolinium (Gd), silver (Ag), indium (In), and hafnium (Hf). They are in the form of any of metals, alloys, intermetallic compounds or ceramics. B in BP member
For example, in the case of gadolinium, the content of the P metal is required to be 2 to 8 wt% with respect to the total weight of the channel box in order to control the initial reactivity. Gd / Zry
As an example of alloy components when the -4 alloy is used as a BP member, tin: 1.20-1.70, iron: 0.18-0.2
4, chromium: 0.7-0.13, oxygen: 0.10-0.
16, gadolinium: 5-80, zirconium: remaining (wt%). In this case, the ratio of gadolinium changes depending on the size and the number of BP members.

FIG. 14A shows (1) (a) that a Zry powder is placed on a BP metal (Gd, Cd, etc.) having a lower melting point than Zry, and heated in a vacuum to the melting point of the BP metal to reduce the BP metal. Z
This is a method of forming the BP member 4 by impregnating voids of ry powder. Conversely, (1) and (b) of FIG. 14 show that a BP having a higher melting point than Zry is placed on a Zry plate or sponge zirconium.
A metal or BP oxide powder is placed and heated in a vacuum to a temperature (1860 ° C.) equal to or higher than the melting point of Zr.
This is a method of forming the BP member 4 by impregnating the voids of the powder.

FIG. 14 (2) (a) shows a method of coating the BP plate 4 with Zry by plating or vapor deposition, etc., and FIG. 14 (2) (b) This is a method of coating a plate material with BP metal.

FIG. 15 shows a manufacturing process of the BP member 4 coated with Zircaloy. As shown in FIG. 15, the BP powder and the Zry powder are mixed with MA (Mechanical Alloin).
g) A heavy working is performed by the method to obtain an MA alloy powder in which BP (metal, oxide) is dissolved in supersaturation. As the MA method, a planetary ball mill P-5 / 4 manufactured by Fritsch was used.
Processing is performed at a constant rotation speed of the disk of 200 rpm and in an Ar gas atmosphere at room temperature for 100 to 150 hours. After that, the prepared MA alloy powder was
Sintering is performed by HIP (isotropic isostatic pressing) at a temperature equal to or higher than ℃ to complete the BP member 4 of a sintered body as shown in FIG. When the BP member 4 of the sintered body is further coated with Zircaloy, the sintered body is placed in a Zry container 6, sealed in a vacuum, and then compacted by HIP to obtain a structure shown in FIG. ), A BP block material 4 coated with Zircaloy can be manufactured. By using this mechanical arrowing method, BP metal having a solid solution amount or more at room temperature,
In addition, the BP oxide can be supersaturated in Zircaloy to form a solid solution.

FIG. 16 is a diagram showing a BP block material coated with Zry powder, BP metal powder or BP oxide powder, which is compacted into a block and then immersed in an appropriate low melting metal liquid. 7 is a method for producing the same.

Other than the method of manufacturing the BP member 4 described above,
There are also the following methods. For example, there is a method in which zircaloy and BP metal are melted by an arc melting method or the like and alloyed. At this time, it is considered that the mechanical properties are inferior to those of the currently used zircaloy, so it is preferable to add an additional element for strengthening.

There is also a method in which BP metal is precipitated in zircaloy as an intermetallic compound to produce a precipitation type alloy.
As a BP metal that forms an intermetallic compound with zirconium,
Cadmium, boron, silver, indium and the like can be mentioned.

Although some embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but may be made within the spirit and scope of the invention described in the appended claims. Various changes can be made in the design.

(Embodiment 6) As a fifth embodiment, there is the following method other than the means for performing quenching as described above and embedding the BP member 4 in the channel box 1 as described above. That is, as shown in FIG. 17, when a BP member 4 coated with another metal is used, a means for attaching the BP member 4 to the side surface thereof without embedding the BP member 4 in the channel box 1 can be considered. FIG. 17 (a) (b)
FIG. 18B shows a case where the coated BP member 4 is disposed in the longitudinal direction near the corner of the outer surface of the channel box 1. FIG.
This is the case where the P member 4 is disposed in the longitudinal direction at the corner on the outer surface of the channel box 1. FIG. 18 (a)
FIG. 19 shows a case where the coated BP member 4 is arranged in the longitudinal direction near the corner of the inner surface of the channel box 1, and FIG. Is the case.

BP to channel box 1 in this case
FIG. 20 shows a method of attaching the member 4. FIG. 20
(A) is a method of attaching the BP member 4 using a rivet 8 made of Zircaloy or stainless steel. In this case, the BP member 4 may be attached to either the inside or the outside of the channel box 1 by the rivets 8. FIG.
(B) shows a method in which the coated BP member 4 is directly welded and attached to the side surface of the channel box 1.

Further, FIG. 21 shows a BP coated with a fixture 9 made of Zircaloy or stainless steel.
This is a method of attaching the member 4.

(Embodiment 7) FIG. 22 shows a sixth embodiment in which β quenching is performed in the same manner as described above, and a BP member 4 coated on the water rod 3 is provided. As shown in FIG. 22, a coated BP metal tube 10 is disposed in the water rod 3 to form a double structure, and a Zry tube 11 is disposed further inside the BP metal tube 10. To make a triple structure.

(Embodiment 8) In Embodiments 1 to 7 described above, the thickness of the channel box is entirely the same. As a seventh embodiment, a burnable poison is contained in the same manner as in the above-described embodiment, and further, β quenching is performed. As shown in FIGS. It was done. The channel box shown in FIGS. 23 and 24 is heat-treated by inserting a SUS304 mandrel as described above, then masked and formed into a predetermined shape by chemical etching using a mixed acid aqueous solution of hydrogen fluoride and nitric acid or by mechanical cutting. It is formed so that the side 21 is thinner than the corner 20 and is concave on the outside (b) or inside (c) of the cylindrical body as shown in FIG. FIG.
Then, the thin portion has the same thickness with respect to the four sides of the quadrilateral. In FIG. 24, the upper and lower sides have different thicknesses.
2 is thinner than the lower portion 23.

It is also possible to omit the cold rolling and annealing after β quenching during the manufacturing process.

The structure in this embodiment is intended to prevent blistering caused by creep deformation due to long-term use. Also for this structure, any of the zirconium-based alloys in which the burnable poisons described in Examples 1 to 3 are engaged and arranged can be used. Similarly, by performing the quenching treatment, bending due to irradiation growth can be prevented.

(Embodiment 9) FIG. 25 shows an eighth embodiment, which is a channel box 1 which has been subjected to β quenching in the same manner as described above and made of a Zry alloy containing BP. As shown in FIGS. 25A and 25B, the shape of the channel box is such that the local peaking coefficient at the corner of the fuel assembly A is effectively suppressed by increasing the thickness of the corner, Further, it is possible to simultaneously suppress the bulging deformation of the corner portion of the channel box 1 due to creep deformation generated under neutron irradiation, and the purpose is the same as that of the eighth embodiment. In addition, by coating the surface with a highly corrosion-resistant alloy such as Zircaloy, the burnable poison does not come into direct contact with the reactor water, and the corrosion resistance can be increased. Tin: 1.20-1.7 is an example of an alloy component when the entire channel box is made of a Gd / Zry-4 alloy.
0, iron: 0.18-0.24, chromium: 0.7-0.13
, Oxygen: 0.10-0.16, gadolinium: 2.0-
8.0, zirconium: The remainder (wt%) is exemplified.

Example 10 Three kinds of zircaloys having the alloy compositions shown in Table 1 were used as the zirconium alloy sheet materials, and were subjected to the heat treatment shown in Table 2. It is zirconium that is deformed by neutron irradiation, and neutron irradiation is performed on a zirconium-based alloy having no burnable poison.

Each alloy is a sheet material having a thickness of 2.5 mm, and has been repeatedly subjected to cold rolling and annealing at 650 ° C. for 2 hours before receiving. Heat treatment No. 2 shown in Table 2
No. 4 heats a plate material having a width of 280 mm and a length of 4 m with a high-frequency induction coil, and a cooling nozzle is wound in a coil shape below the high-frequency induction coil to uniformly cool the water over the entire circumference. It was done by doing. The parameter P is obtained by the above equation. In order to heat the entire plate width to a uniform temperature, the upper and lower parts of the coil are left and right by rollers so that the gap between the plate and the coil does not change.
In addition to preventing movement before and after, the coil has three turns, and the heating width per turn is 1 cm or more, preferably 1.5 to
The heating temperature was made uniform so that the width of the heating zone was 2 cm or more and 4 cm or more. For cooling, warm water of 40 ° C. or higher was used to eliminate deformation due to cooling, thereby enabling uniform heating. No deformation of the plate material in this example was visually observed.

[0088]

[Table 1]

[0089]

[Table 2]

Table 3 shows (0002) of No. 1 to 6 heat-treated materials.
The F-number measurement result of the plane (parallel to the (0001) plane) is shown. F
The value is measured by a combination of the reflection and transmission X-ray diffraction methods described above. Fr is the orientation ratio in the direction perpendicular to the surface of the tubular member, Fl is the orientation ratio in the longitudinal direction, and Ft is the orientation ratio in the circumferential direction.

Since the F value of the heating / cooling plate (heat treatment No. 2) in the α + β phase temperature range is almost equal to that of the receiving material (heat treatment No. 1), the texture in the heating / cooling to the α + β phase temperature range is It turns out that it does not change. Cooling after holding for 1 minute and 5 seconds in the β phase temperature range (1000 ° C)
(Heat treatment Nos. 3, 6) is (0002)
A decrease in the Fr value of the plane and an increase in the Fl and Ft values are recognized, and the crystal orientation is randomized. However, the neutron dose ≧ 10
^It does not satisfy the target value Fr value ≦ 0.35 which is a target value for enabling use even in a high irradiation range of ²² (n / cm ² ). 1000
C. for 10 minutes (heat treatment No. 4) and 120
When the heating temperature was increased to 0 ° C. (heat treatment No. 5), (0
The F value of the (002) plane is about 0.33, indicating that the crystal orientation is almost completely randomized. As previously mentioned,
No. 4 and 5 heat-treated materials do not bend or elongate even in a high irradiation area and even when the irradiation amount of neutrons is uneven in the member.

[0092]

[Table 3]

FIG. 26 is a diagram showing the relationship between the amount of fast neutron irradiation and the amount of irradiation growth. As shown in FIG.
Under 3 or below, the strain increases rapidly with an increase in the neutron irradiation dose, but under 0.3 or above, the strain saturates even after irradiation, and does not increase. In particular, Fl = 0.33
Since the <0001> crystal orientation is substantially randomly oriented, the strain in the normal direction, the longitudinal direction and the thickness direction is canceled out among the crystals, so that the burn-up of 6
At 0 GWd / t, it does not occur at all at 1 mm or less at a length of 4 m. In the case of Fl = 0.3, the irradiation growth amount is as small as 2 mm or less up to the irradiation dose of 10 ²² n / cm ² , but in the case of Fl above that, the growth gradually increases with the neutron irradiation amount.

FIG. 27 is a diagram showing the relationship between the Fl value and the irradiation growth amount by irradiation corresponding to the burn-up of 36, 45 and 60 GWd / t. The strain increases sharply as the Fl value decreases. In particular, the irradiation growth amount at Fl = 0.33 is zero, which is remarkably less than about 1/7 of Fl = 0.3.
Also, Fl = 0.3 is remarkably less than about one third of Fl = 0.23. However, when Fl = 0.23, Fl = 0.16
And Fl = 0.16 is about half of Fl = 0.09.

FIG. 28 shows the βZr crystal grain size and (0002)
The relation with the Fl value of the surface is shown. When the βZr crystal grains grow to a crystal grain size of 200 μm or more, the Fl value is 0.33.
It can be seen that the following texture is formed.

By growing the grains (000
2) The crystal orientation of the plane can be randomized, and the degree of randomization of the orientation is about 7 with an Fl value of 0.30.
5%, at which time the particle size is about 100 μm. 1
With a crystal grain size of 50 μm or more, about 8
It is randomized to 0% or more, and the Fl value becomes 0.310. Further, the random ratio at an Fl value of 0.33 is about 90% or more, and the crystal grain size at that time is about 250 μm or more.

FIG. 29 shows the βZr crystal grain size and burnup of 60 GW.
FIG. 3 is a diagram showing a relationship between the irradiation growth amount by fast neutron irradiation corresponding to d / t. As shown in the figure, when the grain size is 90 μm or more, the growth amount is zero and is extremely low. At 50 μm, the growth amount is 2 mm or less, especially at 35 μm or less, the growth amount rapidly increases. Excellent characteristics can be obtained with a growth amount of 60 mm or more and 1 mm or less.

The parameter P in the table = (3.55 + logt)
× log (T-980) and irradiation growth strain,
In particular, in the heat treatment at 1000 ° C., the irradiation growth strain sharply decreases when P is 0.5 or more, gradually decreases from 0.5 to 3.5, becomes almost constant at 3.5 or more, and approaches zero. Irradiation growth occurs when P is less than 3.5, but hardly occurs above P. In particular, the effect is large at 1.5 or more, and 3.2 to 5 is preferable.

FIG. 30 shows Table 1 at each temperature and holding time.
5 is a diagram showing a relationship between Fl values of the alloys shown in Table 4 and Table 4. FIG.
As shown in the drawing, when the temperature is lower than 980 ° C., the Fl value becomes 0.20 or less, and it is difficult to obtain a crystal having a random <0002> crystal orientation. However, at 980 ° C, 11 seconds (1000 ° C
If heating at 1240 seconds or more or heating at 1240 ° C. or more for 1.1 seconds or more on the line connecting these points, an Fl value exceeding 0.25 can be obtained, and those having higher randomness can be obtained. can get. Heating at 980 ° C. or more for 6 seconds or more and 1240 ° C. or more for 6 seconds or more, and above the line connecting these points, Fl values larger than 0.20 and 0.25 or less can be obtained. Those lower than this line have an Fl value of 0.20 or less, have a low degree of randomness, and have a small effect on elongation.

[0100]

[Table 4]

As described above, if the crystal orientation can be completely randomized, irradiation growth distortion due to neutron irradiation does not occur. However, the actual channel box is a square cylinder, one side of which is 140 mm. It is difficult to form the F value at the surface completely the same. The aforementioned irradiation growth strain is due to the difference in F value, but the problem in the channel box is bending. The bending is particularly caused by the difference in the F value between the facing surfaces. By changing the heat treatment conditions described above, a slight difference was formed in the F value at the facing surface, and the amount of bending was measured.

FIG. 31 shows an F-number (F) in the longitudinal direction having a length of 4 m.
FIG. 11 is a diagram showing the amount of bending due to the difference ΔF1 between the l) and the Fl value at the facing surface. The amount of bending is 35 as the burnup.
GWd / t, which is 2.16m, which is the limit of bending
m indicates the allowable value in the gap between the channel box and the control rod. As shown in the figure, it can be seen that the ΔFl value on the facing surface reaching a bend of 2.16 mm according to each Fl value can be increased as the crystal orientation is randomized. In particular, as ΔFl, the Fl value of the facing surface is set at a plurality of locations,
Particularly preferably, it is preferable to equally divide four or more portions, obtain an average Fl value of the portion, and measure the difference between the average Fl values.

FIG. 32 is a graph showing the relationship between the Fl value and the difference (ΔFl) of the Fl value at the circumferential facing surface with respect to the limit value of the bending at the burnup of 35 GWd / t. The allowable ΔFl value is proportional to the Fl value. If the vertical axis ΔFl is y and the horizontal axis Fl is x, y = 0.093
A uniform heat treatment represented by 5x-0.00585, which is below the diagram, can be within the limit of bending. In order to heat the channel box shown in this embodiment at a uniform temperature with respect to the thickness, width and length required for the channel box, as described above, the number of turns of the induction heating coil, the width of the heating zone, and the cooling It is necessary to optimize the speed and equalize the gap between the plate and the coil.

Further, the channel box undergoes creep deformation due to water pressure, thereby causing swelling deformation. The swelling deformation occurs when the fuel level is further increased.
In / t, the amount of bending and the amount of swelling must be considered.

Tables 5 and 6 show the dependence of the channel bending amount (mm) on Fl and ΔFl at 60 GWd / t. Considering the swollen amount, the bend amount is 1.17 m.
m or less, and Fl is 0.30 to 0.3.
5, ΔFl is preferably 0.006 or less.

[0106]

[Table 5]

[0107]

[Table 6]

[0108]

As can be understood from the above description, the plutonium-mixed fuel assembly (MOX fuel assembly) of the present invention can be used without excess neutron absorbing material or burnable poison inside fuel rods. Since the reactivity can be appropriately suppressed and the crystal orientation of the fuel assembly Zircaloy member can be randomized, even when used in a high irradiation environment where the neutron irradiation amount exceeds 10 ²² (n / cm ² ), irradiation can be performed. The bending deformation caused by the growth does not occur, and the shuffle can be minimized. As a result, the fuel assembly zirconium member can be used for a high burn-up reactor which is used for a long time, and can contribute to the reduction of spent fuel waste. Further, the corrosion resistance is also improved, the deformation of the bulge due to the thermal creep deformation is suppressed, the leakage flow rate can be reduced, and the reliability of the fuel assembly zirconium member can be improved.

Further, since the burnable poison is not mixed into the fuel, the use of plutonium in a light water reactor can be realized without reducing the amount of plutonium loaded per fuel assembly.

Further, it is possible to effectively reduce local peaking in the outer peripheral portion of the fuel assembly without increasing the type of pellet enrichment, thereby enriching the pellets constituting the fuel assembly. The degree can be reduced.

Further, the burnable poison is buried in the channel box, or the burnable poison is coated with a metal such as Zircaloy, so that the burnable poison itself and the crevice corrosion between the channel box and the burnable poison are corroded. And the galvanic corrosion does not occur, and the burnable poison itself does not come into direct contact with the reactor water, so that the burnable poison can be prevented from being eluted into the reactor water.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view and a side view of a channel box of a first embodiment of the present invention in which a BP member is embedded (near a corner).

FIG. 2 is a sectional view and a side view of a channel box of a BP member embedded type (corner part) according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a manufacturing process (pre-stage process) of the channel box of the embodiment of FIGS. 1 and 2;

FIG. 4 is a configuration diagram showing a manufacturing process (post-stage process) of the channel box of the embodiment of FIGS. 1 and 2;

FIG. 5 is a configuration diagram showing another manufacturing process of the channel box of the embodiment of FIGS. 1 and 2;

FIG. 6 is a perspective view of an apparatus for quenching a zirconium-based alloy plate.

FIG. 7 is a cross-sectional view of a fired material assembly.

FIG. 8 is a sectional view and a perspective view of a channel box of a BP member embedded type (corner part) according to a third embodiment of the present invention.

FIG. 9 is a cross-sectional view and a perspective view of a BP member embedded type (near a corner) channel box according to a fourth embodiment of the present invention.

FIG. 10 is a side view showing an arrangement structure of a BP member in a channel box according to another embodiment of the present invention.

FIG. 11 is a side view showing an arrangement structure of a BP member in a channel box according to still another embodiment of the present invention.

FIG. 12 is a power distribution diagram in a core axis direction.

FIG. 13 is a side view showing an arrangement structure of a BP member in a channel box according to still another embodiment of the present invention.

FIG. 14 is a view showing the structure of a BP member according to the present invention.

FIG. 15 is a configuration diagram showing a manufacturing process of the BP member of the present invention.

FIG. 16 is a configuration diagram showing another manufacturing process of the BP member of the present invention.

FIG. 17 is a cross-sectional view and a side view of a channel box of a BP member (near a corner) according to another embodiment of the present invention.

FIG. 18 is a sectional view and a side view of a channel box of a BP member according to still another embodiment of the present invention.

FIG. 19 is a sectional view and a side view of a channel box of a BP member according to still another embodiment of the present invention.

FIG. 20 is a cross-sectional view and a side view showing a mounting structure of the BP member of the present invention to a channel box.

FIG. 21 is a cross-sectional view and a side view showing another mounting structure of the BP member of the present invention to a channel box.

FIG. 22 is a perspective view showing a mounting structure of the BP member of the present invention to a water rod.

FIG. 23 is a sectional view and a perspective view of a channel box of a BP member according to still another embodiment of the present invention.

FIG. 24 is a perspective view of a channel box of a BP member according to still another embodiment of the present invention.

FIG. 25 is a perspective view of a channel box made of a BP-containing zirconium alloy of the present invention.

FIG. 26 shows the effect of fast neutron irradiation on irradiation growth strain,
And a diagram showing the effect of the Fl value.

FIG. 27 is a diagram showing the relationship between irradiation growth strain and Fl value.

FIG. 28 is a diagram showing the relationship between the Fl value and βZr crystal grains.

FIG. 29 is a diagram showing the relationship between irradiation growth strain and Zr crystal grain size.

FIG. 30 is a diagram showing the relationship between irradiation growth strain, quenching temperature, and holding time.

FIG. 31 is a diagram showing a relationship between a ΔFl value and a bending amount.

FIG. 32 is a diagram showing the relationship between the Fl value and ΔFl.

FIG. 33 is a diagram showing a change in control value with neutron irradiation dose.

FIG. 34 is a diagram showing a relationship between a neutron energy and a neutron absorption cross-sectional area of a burnable poison and a neutron absorbing material.

FIG. 35 is a thermal neutron flux distribution diagram in a fuel assembly.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Channel box, 2, 11 ... Fuel rod, 3 ... Water rod, 4 ... BP member, 12 ... Spacer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junjiro Nakajima 3-1-1, Sakaimachi, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Plant

Claims (24)

[Claims] 1. A fuel rod bundle in which a plurality of nuclear fuel rods containing uranium or plutonium are arranged, and Sn surrounding the fuel rod bundle.
5% by weight or less and / or 5% by weight or less of Nb,
In a fuel assembly provided with a channel box made of a zirconium-based alloy having 0 wt% or more of Zr, the hexagonal Zr of the alloy has an orientation ratio (Fl value) of 0.1 in the plate length direction of the <0001> crystal orientation. A fuel assembly, characterized in that a burnable poison is contained in a channel box made of a low-irradiation-grown zirconium-based alloy having a diameter of 20 to 0.35. 2. A fuel rod bundle in which a plurality of nuclear fuel rods containing uranium or plutonium are arranged, and Sn surrounding the fuel rod bundle.
5% by weight or less and / or 5% by weight or less of Nb,
A channel box made of a zirconium-based alloy having Zr of 0% by weight or more,
A channel box made of a low-irradiation-grown zirconium-based alloy in which the crystal grain size of the alloy is 50 to 500 μm and the orientation ratio of the crystal orientation of the alloy is substantially the same at the center and the end in the plate width direction. A fuel assembly comprising a burnable poison. 3. A fuel rod bundle in which a plurality of uranium or plutonium-containing nuclear fuel rods are arranged, and Sn surrounding the fuel rod bundle.
5% by weight or less and / or 5% by weight or less of Nb,
A fuel assembly having a channel box having a length of 4 m or more made of a zirconium-based alloy having 0 wt% or more of Zr, wherein the <0001> crystal orientation of hexagonal Zr of the alloy is substantially random, and Burnup 35 GW
The amount of bending at a length of 4 m due to neutron irradiation of d / t is 2.
A fuel assembly, characterized in that a burnable poison is provided in a channel box made of a low-irradiation-grown zirconium-based alloy of 16 mm or less. 4. A fuel rod bundle in which a plurality of uranium or plutonium-containing nuclear fuel rods are arranged, and Sn surrounding the fuel rod bundle.
5% by weight or less and / or 5% by weight or less of Nb,
A channel box made of a zirconium-based alloy having Zr of 0% by weight or more,
The orientation ratio (Fl value) of the <0001> crystal orientation of the hexagonal Zr of the alloy in the plate length direction is 0.20 to 0.35, and the difference (ΔFl) in the Fl value between the opposing surfaces is 0.025. Is the following,
A fuel assembly, characterized in that a burnable poison is contained in a channel box made of a low-irradiation-grown zirconium-based alloy in which β-phase Zr grains have no subgrain boundaries. 5. The method according to claim 1, wherein the burnable poison is buried so as not to come into direct contact with the reactor water.
The fuel assembly according to any one of claims 1 to 4. 6. The burnable poison is coated with a highly corrosion-resistant alloy or metal such as Zircaloy so as not to come into direct contact with the reactor water.
A fuel assembly according to any one of the preceding claims. 7. The burnable poison is disposed in a water rod disposed in a channel box, and the burnable poison is made of a highly corrosion-resistant alloy or metal such as Zircaloy so as not to come into direct contact with reactor water. The fuel assembly according to any one of claims 1 to 4, wherein the fuel assembly is coated. 8. The fuel assembly according to claim 1, wherein a corner of the channel box is thicker than a side. 9. The fuel assembly according to claim 1, wherein the burnable poison is a metal, an alloy, an intermetallic compound, or a ceramic. 10. The burnable poison is a metal, alloy, intermetallic compound or ceramic containing at least one of cadmium, samarium, boron, gadolinium, silver, indium, and hafnium. The fuel assembly according to any one of claims 1 to 8. 11. The burnable poison according to claim 1, wherein at least one of cadmium, samarium, boron, gadolinium, silver, indium, and hafnium is added to zirconium or a zirconium-based alloy as an alloying element. The fuel assembly according to any one of claims 1 to 8, wherein at least one of oxide, hydride, and nitride is dispersed or dissolved in a supersaturated state. 12. A dent is provided in one zirconium-based alloy material plate of a channel box, and a plate of a burnable poison is engaged and disposed in the dent, and another plate is inserted so that the burnable poison is embedded. After covering with a zirconium-based alloy material plate and joining by hot rolling or hot pressing, cold rolling and annealing are appropriately repeated, and then the material plate is heated to a β-phase single-phase temperature region while being continuously moved. And producing a zirconium-based alloy plate containing a combustible poison. 13. A zirconium-based alloy material plate having a dent formed in one channel box, and a plate of a burnable poison is engaged with the dent, and the other plate is embedded so that the burnable poison is embedded therein. After covering with a zirconium-based alloy material plate of the above and joining by hot rolling or hot pressing, cold rolling and annealing are repeated as appropriate, and then the material plate is elongated in the <0001> crystal orientation of hexagonal Zr of the alloy. So that the orientation ratio (Fl value) in the direction is 0.20 to 0.35.
The flammability according to claim 12, further comprising: a step of rapidly cooling after heating and holding in a single-phase temperature region for a short time, and a method of reducing the heating temperature difference between a central portion and an end portion in a plate width direction. A method for producing a poison-containing zirconium-based alloy plate. 14. A zirconium-based alloy material plate having a dent in one channel box, and a plate of a burnable poison engaged with the dent, and the other plate is embedded so that the burnable poison is embedded therein. After covering with a zirconium-based alloy base material sheet, joining by hot rolling or hot pressing, and appropriately repeating cold rolling and annealing, the zirconium base material is heated to the β-phase single-phase temperature region and cooled. In the method for manufacturing an alloy plate, the alloy plate is continuously passed through a high-frequency induction heating coil wound a plurality of times to be heated, and is cooled by injecting a coolant from a cooling nozzle provided at the rear of the coil. A method for producing a zirconium-based alloy plate containing a burnable poison, comprising the steps of: 15. A dent is provided in one zirconium-based alloy material plate of a channel box, and a plate of a burnable poison is engaged and arranged in the dent, and the other plate is embedded so that the burnable poison is embedded therein. After covering with a zirconium-based alloy material plate, hot rolling or hot pressing and joining, and then appropriately repeating cold rolling and annealing, the material plate is locally heated to a β-phase single-phase temperature region by induction heating. A method for producing a combustible poison-containing zirconium-based alloy plate in which the heated portion is forcibly cooled by a refrigerant and the heated portion is forcibly cooled by a <0001> crystal orientation of the hexagonal Zr of the alloy in the plate longitudinal direction. Orientation ratio (Fl value) is 0.20 to 0.35
A short-time heating and holding in the β-phase single-phase temperature region and then quenching, and the heating step is a method of reducing variation in the orientation ratio (Fl value) in the longitudinal direction of the zirconium-based alloy plate. A method for producing a zirconium-based alloy tubular member containing a low-irradiation-growth burnable poison, characterized by comprising: 16. A dent is provided on one zirconium-based alloy material plate of a channel box, and a plate of a burnable poison is engaged and arranged in the dent, and the other plate is embedded so that the burnable poison is embedded therein. Covered with a zirconium-based alloy material plate, hot-rolled or hot-pressed, joined, and then cold-rolled and annealed repeatedly as needed to continuously move the plate locally to the β-phase temperature region by induction heating. A method for producing a burnable poison-containing zirconium-based alloy plate, wherein a quenching process is performed to perform heating and forcibly cooling the heated portion with a refrigerant, wherein the quenching process is performed a plurality of times. A method for producing a zirconium-based alloy member containing a poison. 17. A <0001> crystal of hexagonal Zr of said alloy in a fuel channel box consisting of a rectangular tubular member welded and joined by using two U-shaped zirconium-based alloy members containing a burnable poison. A fuel channel box, wherein the orientation ratio (Fl value) in the longitudinal direction of the cylindrical member in the direction is 0.20 to 0.35. 18. A fuel rod containing a fuel pellet in a fuel cladding tube, a channel box for accommodating a plurality of the fuel rods, a spacer for partitioning the fuel rods in the channel box, and upper and lower portions of the channel box. In the fuel assembly provided with the upper lattice plate and the lower lattice plate provided, the channel box is provided with Zr of 5% by weight or less of Sn and / or 5% by weight of Nb and 90% by weight or less of the balance, in which the burnable poison is engaged. A hexagonal Zr of the alloy has an orientation ratio (Fl value) of the <0001> crystal orientation in a longitudinal direction of 0.20 to 0.35, and the difference of Fl on the opposing surface is Is 0.025 or less. 19. A zirconium-based alloy material plate in which a combustible poison is engaged and mixed, is subjected to a quenching process of quenching from a β-phase temperature region, then to a cold working and an annealing process, and then to a U-shaped bending process and an annealing process. And a method of manufacturing a fuel channel box in which abutting portions are welded to form a square tube. 20. A combustible poison plate is interposed between two zirconium-based alloy base plates, the three plates are hot-rolled and pressed, and then cold-rolling and annealing are repeated an appropriate number of times. A method for producing a zirconium-based alloy plate containing a burnable poison, wherein the plate is heated to a β-phase single-phase temperature range while the plate is continuously moved and cooled. 21. A combustible poison plate is interposed between two zirconium-based alloy base plates, the three plates are hot-rolled and pressed, and then cold-rolling and annealing are repeated an appropriate number of times. After heating the plate for a short time in the β-phase single-phase temperature region, the plate is heated so that the orientation ratio (Fl value) in the longitudinal direction of the <0001> crystal orientation of the hexagonal Zr of the alloy becomes 0.20 to 0.35. The combustible poison-containing substance according to claim 20, further comprising a step of quenching, wherein the heating in the β-phase single-phase temperature region has a method of reducing the heating temperature difference between a central portion and an end portion in a plate width direction. A method for manufacturing zirconium-based alloy sheets. 22. A combustible poison plate is interposed between two zirconium-based alloy base plates, the three plates are hot-rolled and pressed, and then cold-rolling and annealing are repeated an appropriate number of times. In the method for producing a zirconium-based alloy plate, wherein the plate is heated to a β-phase single-phase temperature region and cooled, the alloy plate is continuously passed through a high-frequency induction heating coil that is wound a plurality of times and heated. A method for producing a zirconium-based alloy plate containing a burnable poison, comprising a step of injecting a coolant from a cooling nozzle provided behind a coil to cool it. 23. A combustible poison plate is interposed between two zirconium-based alloy base plates, the three plates are hot-rolled and pressed, and then cold-rolling and annealing are repeated an appropriate number of times. The method for producing a burnable poison-containing zirconium-based alloy plate in which a plate is locally heated to a β-phase single-phase temperature region continuously by induction heating and the heated portion is forcibly cooled by a refrigerant, <0 of the hexagonal Zr of the alloy
001> heating and holding in the β-phase single-phase temperature region for a short time so that the orientation ratio (Fl value) of the crystal orientation in the longitudinal direction of the plate becomes 0.20 to 0.35; Orientation rate of the zirconium-based alloy plate in the longitudinal direction (F
A method for producing a low-irradiation growth burnable poison-containing zirconium-based alloy cylindrical member, comprising a method of reducing the variation in the heating temperature in order to reduce the variation in the l value). 24. A combustible poison plate is interposed between two zirconium-based alloy base plates, the three plates are hot-rolled and pressed, and then cold-rolling and annealing are repeated an appropriate number of times. A burnable poison-containing zirconium-based alloy plate which is continuously heated while being relatively moved locally by induction heating to a β-phase temperature region and which is subjected to a quenching treatment for forcibly cooling the heated portion with a refrigerant. The method for producing a zirconium-based alloy member containing a burnable poison, wherein the quenching treatment is performed a plurality of times.