JPH0943394A - Boiling water reactor and nuclear power plant equipped with boiling water reactor - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the corrosive environment of reactor water and reduce the amount of radioactive nitrogen generated in a boiling water reactor without providing an external control system. [Structure] A fuel rod cladding tube 23 loaded in the core 1 of a boiling water reactor is provided with a heat pipe 21 in contact with the nuclear fuel filled in the fuel rod cladding tube, and heat generated by the nuclear fuel is supplied to the core fuel. It is configured to be conveyed upstream from the loading section. [Effect] Since boiling starts on the upstream side of the neutron irradiation field, the hydrogen injected into the reactor water is released to the gas phase by the boiling of the reactor water, and the residence time of water in the neutron and gamma ray irradiation field is reduced. , Etc. reduce the total amount of radiolysis products and radioactive nitrogen generated in water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear reactor and a nuclear power plant capable of mitigating the corrosive environment of reactor water without particularly providing an external control system.

[0002]

2. Description of the Related Art Intergranular stress corrosion cracking of a reactor structural material (hereinafter referred to as IGSCC) occurs when all three factors of material composition, stress, and water quality (dissolved oxygen content in reactor water) are in an unfavorable state. Has been done. Conventionally, reactor structural materials, particularly SUS304 steel, have been subjected to a heat treatment for reducing the carbon content, residual stress relaxation, etc.
From the perspective of CC, it has been operated on the safe side. As described above, the measures so far have been for the two factors of the material and the stress among the three factors of IGSCC, but in the boiling water reactor in recent years, the reactor water, which is one of the three factors, is used. In order to reduce dissolved oxygen, hydrogen injection has been attempted as seen in JP-A-57-3086.

FIG. 2 shows the main components of a boiling water nuclear power plant. The boiling water nuclear power plant shown in FIG.
2, a reactor core 1 that is installed in a pressure vessel 22 and supported by a core support plate 20, a lower plenum 7 formed below the core support plate 20, and a reactor core (hereinafter referred to as core) 1
Is placed around the circumference of the pressure vessel and downcomer 5
Which forms a mixing plenum 4 between the cylindrical shroud 19 which forms the upper end of the core 1, the upper plenum 2 which is arranged in contact with the upper end of the core 1, and the side wall of the pressure vessel 22 which is arranged above the upper plenum 2. Main steam pipe 1 that connects the separator 3 and the space above the steam separator 3 to the steam turbine 11.
5 and a condenser 12 arranged in contact with the steam turbine 11.
And the condensate demineralizer 10 arranged in connection with the condenser 12.
And the condensate demineralizer 10 to the feed water pump 18 and feed water heater 9
Via a water supply pipe 14 connected to the mixing plenum 4 of the pressure vessel, a hydrogen injection device 13 connected to the water supply pipe between the condensate demineralizer 10 and the water supply pump 18, Circulation pump suction side piping 16A
A recirculation pump 6 having a suction side connected thereto via a recirculation pump 6, a recirculation pump discharge side pipe 16B connecting a discharge side of the recirculation pump 6 and a lower portion of a jet pump riser pipe 16C arranged in the downcomer 5, and a jet pump riser Tube 16
A jet pump 17 which is connected to the upper part of C and is arranged in the downcomer 5 to send the reactor water in the mixing plenum 4 to the lower plenum 7 by using the water discharged from the jet pump riser pipe 16C as a drive source, and the recirculation pump suction side. Reactor purification system 8 arranged by connecting the inlet side of the pipe 16A and the outlet side of the feed water pipe 14 on the downstream side of the feed water heater.
And is configured.

Fuel assemblies 32 are loaded on the core 1 in a grid pattern, and the fuel pellets 2 are attached to each fuel assembly 32.
Fuel rod cladding tubes 23 filled with 4 are installed at predetermined intervals. The reactor water flows upward from the lower plenum 7 inside (boiling channel) and outside (bypass channel) of the fuel assembly 32, receives the heat generated by the nuclear fuel, is heated, and boils. Steam is separated from the reactor water that has boiled into a gas-liquid two-phase by the steam separator 3 and is sent to the turbine 11 through the main steam pipe 15. The remaining reactor water is mixed with the feed water in the mixing plenum 4 and sent to the lower plenum 7 again by the jet pump 17. The steam that has consumed energy in the turbine 11 is condensed and liquefied in the condenser 12, is desalted by the condensate demineralizer 10, is pressurized by the feed water pump 18, and is sent to the feed water heater 9. The feed water heated by the feed water heater 9 is fed again to the mixing plenum 4 of the pressure vessel 22. A part of the feed water (reactor water) sent to the mixing plenum 4 is suction-driven by the jet pump 17 and sent to the lower plenum 7 to repeat the above cycle, and the rest flows down the downcomer 5 downwards, It is sucked into the recirculation pump 6.

The recirculation pump 6 sucks in the reactor water below the downcomer 5, pressurizes it, and supplies it to the jet pump 17 as driving water. Reactor water supplied to the jet pump as driving water is also sent to the lower plenum 7 to repeat the above cycle.

In the example of injecting hydrogen in the water supply system after the condenser of the primary cooling system of this boiling water nuclear power plant, the hydrogen injection device 13 is arranged upstream of the water supply pump 18 and the injected hydrogen is used as water in the core. The aim was to re-combine oxygen and hydrogen peroxide generated as a result of radiolysis to reduce the dissolved oxygen concentration in each part of the primary cooling system including the recirculation pump 6.

FIG. 3 shows the measurement results of the oxygen concentration in the reactor water measured outside the reactor when hydrogen was injected, for plants in Japan and overseas. As can be seen from the figure, although there are differences depending on the plant, the dissolved oxygen in the reactor water can be reduced to a level of 20 ppb or less, which is required to suppress crack growth due to SCC, with a relatively small amount of hydrogen injection.

The biggest problem of hydrogen injection is N-16 which is generated in water as a result of adding hydrogen and making the water quality of the reactor water become a reducing atmosphere.
Among them, the rate of conversion to volatile ammonia increases, and the radiation dose rate (hereinafter referred to as dose rate) in turbine system piping and equipment increases. Fig. 4 shows a practical example. From the figure, when hydrogen is injected, the hydrogen concentration in the feed water is 400 ppb.
It can be seen that the main steam system dose rate rapidly increases beyond the front and back. As shown in the reaction mechanism diagrammatically in Fig. 5, this is due to the radioactive nitrogen (half-life of 7.1) that is normally generated by the (n, p) reaction from oxygen atoms in water molecules in an oxidizing atmosphere.
Second) reacts with the decomposition products of water in water and is usually dissolved in water in the form of nitric acid or nitrous acid, whereas the addition of hydrogen increases the concentration of reducing hydrogen atoms and hydrated electrons. Therefore, it can be understood that the amount of volatile ammonia increases.
Since the main steam is guided to the turbine 11 arranged in the turbine building, an increase in the main steam system dose rate causes an increase in the turbine system dose rate. Since the turbine system dose rate controls the dose rate at the site boundary of the nuclear power plant, the hydrogen addition amount is practically 400 ppb.
The above increase will not be possible with domestic reactors with a narrow site.

A simulation analysis of radiolysis of BWR water shows that if the hydrogen concentration in the feed water is set to 400 ppb, a corrosive environment mitigation effect in the furnace, especially a corrosive environment mitigation effect at the furnace bottom can be expected. An example of the evaluation result by theoretical analysis is shown in FIG. Oxygen, hydrogen, and hydrogen peroxide are present in reactor water in relatively high concentrations, and each has an inherent effect on material corrosion, but the corrosion potential is widely adopted as a unified indicator of material stress corrosion cracking susceptibility. . FIG. 6 shows the distribution in the pressure vessel of the corrosion potential calculated from the calculation results of water decomposition products based on the mixed potential theory. The left side of Fig. 6 shows the result when normal operation is performed, and the right side shows the result when hydrogen is injected from the water supply system to a hydrogen concentration of 0.4 ppm in the water supply, and the corrosive environment of the structural material under the pressure vessel is greatly mitigated. Is shown to be done. As shown in the figure, when hydrogen is not added, the corrosive environment is severe throughout the furnace, whereas adding 0.4 ppm of hydrogen in the feed water (corresponding to 50 ppb in the reactor water) can sufficiently reduce the corrosive environment at the bottom of the furnace. Recognize. Therefore, it is possible to mitigate the corrosive environment of the furnace bottom without increasing the dose rate of the turbine system. However,
Materials near the core (shrouds, core support plates, etc.) cannot be said to have sufficient environmental improvement at 0.4 ppm in the feed water, and it is necessary to increase the hydrogen injection amount.

It has been similarly obtained from simulation calculations that the concentration of corrosive components in the reactor water changes by changing the flow conditions of the reactor core. Basically, the higher the dose of water accumulated near the core, the more severe the corrosive environment as hydrogen peroxide accumulates in the water. Moreover, when the flow conditions of the core change and the residence time of water in the neutron irradiation field becomes long, the production amount of radioactive nitrogen also increases. That is, by changing the flow conditions near the core and shortening the residence time of the reactor water in a high dose rate irradiation field, the concentration of radiolysis products of water in the reactor water and the amount of radioactive nitrogen generated are reduced. It is possible.

JP-A-55-94191 and JP-A-58-15688
To ensure the efficiency and stability of a nuclear reactor, as described in JP-A-8, JP-A-59-217188, JP-A-60-53878, JP-A-62-106395, etc. , The idea of preheating reactor water has been proposed. In these ideas, an external heat source is used and the heat exchanger is arranged, for example, in a downcomer or at the bottom of the furnace, but there was a problem in control such as the need for an independent control system.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to adjust a heat flow condition and a flow path of a core in a boiling water reactor and a nuclear power plant equipped with the boiling water reactor without providing a special control system. However, it is to efficiently improve the corrosive environment during normal operation and hydrogen injection without increasing the amount of radioactive nitrogen released into the main steam system.

[0013]

In order to achieve the above object, the present invention is concentrically arranged so that heat generated in the core is transferred to the upstream side of the core, and the transferred heat is used to preheat reactor water. A boiling start point of the reactor water is formed by means such as forming a shroud with a plurality of partition walls, forming a vertical water flow region partitioned by the partition walls, and preheating the reactor water flowing in the region with the heat of the reactor core. Is moved as much as possible upstream of the neutron irradiation field to shorten the residence time in the liquid phase of the neutron and gamma ray irradiation field of the reactor water.

As a means for transporting the heat of the core to the upstream side of the core, a heat pipe directly joined to the nuclear fuel loading portion of the fuel rod can be used.

In order to achieve the above object, the present invention also provides:
A vertical water flow region is defined between the inner surface of the shroud and the core to increase the flow velocity of the reactor water on the inner surface of the shroud.

[0016]

[Function] As a result of irradiation of reactor water in the reactor core and in the vicinity of high dose rate fields, water decomposition products are produced in the reactor water, and the concentration of the water decomposes the dose rate and the retention of reactor water in that region. Depends on time. Accumulation of hydrogen peroxide cannot be ignored in the region of low flow velocity and high accumulated dose.

FIG. 7 shows a region corresponding to a region between the core support plate 20 and the upper lattice plate 39, assuming that the flow velocity on the inner surface of the shroud surrounding the core side face of the nuclear reactor is slower than the average flow velocity of the core portion. It shows the analysis result of the distribution of the corrosion potential of the shroud. According to the figure, hydrogen peroxide accumulates on the inner surface of the shroud due to the above-mentioned retention effect, and the corrosion potential becomes severer near the upper part of the core, resulting in a result close to 200 mV. The same effect of hydrogen injection is expected on the inner surface of the shroud, but S
It does not reach -230 mV, which is said to cause no CC. -230mV is not an absolute target, but -100mV
Even with V, it is expected that the SCC crack growth rate will be reduced by an order of magnitude. However, the above result is the case where there is an upward flow on the inner surface of the shroud at a later time, and the actual flow state of the inner surface of the shroud is not necessarily clarified. In some cases, it may be stagnant or in a downward flow, and in this case, hydrogen injection effect cannot be expected. That is, if a relatively fast upflow is formed on the inner surface of the shroud, the corrosive environment during normal operation is almost at a level close to the lower part of the core (corrosion potential of about 50 mV), and the effect of hydrogen injection can be surely expected. By forming a vertical water flow region between the inner surface of the shroud and the core to increase the upward flow velocity of the reactor water on the inner surface of the shroud, the corrosive environment of the inner surface of the shroud is improved. It

On the other hand, radioactive nitrogen is produced by a nuclear reaction between oxygen atoms in reactor water and high-ergic neutrons. Radioactive nitrogen 16 has a short half-life of 7.1 seconds, but 6.1 MeV
It emits high energy gamma rays along with the decay, which is the main cause of the increase in the dose rate of the primary piping of the reactor plant during operation. However, the primary system piping is sufficiently shielded from the outside, and there is no problem because a person does not enter near the primary system piping during operation. In addition, radioactive nitrogen 16
Reacts with hydrogen atoms in water to form ammonia, but when it becomes volatile components such as ammonia, it is released along with steam into the turbine piping, which is the main cause of increasing the dose rate at the turbine building and site boundaries. Since the radioactive nitrogen 16 reacts with hydrogen atoms in water to become ammonia, if the time during which the radioactive nitrogen 16 stays in water is shortened, the amount of ammonia becomes less.

The radioactive nitrogen 16 has a short life, but the residence time in the core is usually 2 seconds or less, so that the amount of generation in the core is almost proportional to the residence time in the neutron irradiation field. The present invention preheats the reactor water before reaching the neutron irradiation field and shifts the boiling start point to a position where the neutron flux is as low as possible, or by boiling before reaching the neutron irradiation field. The main point is to increase the phase flow region. The heat generated in the core is transferred to the upstream side of the core, and the transferred heat is used to preheat the reactor water. The shroud is composed of a plurality of concentric partition walls, and the vertical water flow is divided by the partition walls. By forming a region and preheating the reactor water flowing through the region with the heat of the core, the boiling point of the reactor water moves upstream of the neutron irradiation field, and the neutron of the reactor water, in the gamma ray irradiation field Residence time in the liquid phase is reduced. In the two-phase flow, the flow velocity of water becomes faster and the residence time in the neutron irradiation field also becomes shorter, so the amount of radioactive nitrogen generated is correspondingly reduced. When the amount of generated radioactive nitrogen decreases, the amount of ammonia that reacts with hydrogen in the reactor water to form ammonia decreases, and the amount of radioactive nitrogen that flows into the turbine system in the form of ammonia decreases. Therefore, it is not necessary to suppress the amount of hydrogen to be injected to improve the water quality of the reactor water, and the required amount of hydrogen can be injected into the reactor water.

[0020]

The present invention will be described below with reference to examples. FIG.
1 is a vertical cross-sectional view of a boiling water reactor according to a first embodiment of the present invention. The illustrated reactor includes a pressure vessel 22 and a pressure vessel 22.
A nuclear reactor core (hereinafter referred to as a core) 1, a cylindrical shroud 19 surrounding the core 1, an upper plenum 2 arranged in contact with the upper end of the core 1, and a core 1 below the core 1. And a heat pipe group 21 that is provided in connection with the nuclear fuel part and that conveys heat generated in the nuclear fuel part to the lower side of the core. The other components are the same as those shown in FIG. 2, and therefore the illustration and description will be omitted. In the present embodiment, the heat pipe group 21 conveys the heat generated in the nuclear fuel part to the lower part of the core (upstream of the core of the flow of the reactor water), and before the reactor water flows into the neutron irradiation field of the core, It preheats or preboils reactor water to reduce the residence time of water in the neutron irradiation field.

In the boiling channel, as shown in FIG. 8, the hydrogen concentration in the reactor water (hydrogen atom concentration in the liquid layer shown on the vertical axis)
Is the injection concentration at the boiling height (four types are listed on the right of the figure,
NWC increases corresponding to normal water chemistry, ie, the state where hydrogen is not injected), but since hydrogen is released into the gas phase after the start of boiling, the hydrogen atom concentration in the liquid phase decreases sharply, Even if the hydrogen injection concentration is different, the hydrogen atom concentration in the liquid phase at the position after the start of boiling does not change significantly. That is, the chemical form of radioactive nitrogen changes in the non-boiling region of the neutron irradiation field, so if the reactor water is boiled at the stage before reaching the neutron irradiation field,
The morphological change of radioactive nitrogen 16 due to hydrogen injection does not proceed. That is, the threshold value of the hydrogen concentration at which the main vapor system relative dose rate increases during hydrogen injection shown in FIG. 4 shifts to the right.

FIG. 9 shows a specific example of the installation of the heat pipe shown in FIG. 1, in which the heat pipe 25 is incorporated under the fuel pellet 24 inside the fuel rod cladding tube 23. In FIG. 10, in order to further improve the heat transfer efficiency, the fuel pellets are hollow fuel pellets 26 having a hollow structure, and the upper portion of the heat pipe 25 is disposed inside the fuel pellets. The rod covering tube 23 is provided with fins 27. A part of the heat generated by the nuclear fission of the fuel pellets is transferred by the heat pipe 25 to the upstream side, that is, in the lower part of the figure, and the reactor water before flowing into the core is preheated by the transferred heat. As a result, the boiling position of the reactor water in the core shifts to the upstream side, and the time during which the reactor water receives the neutron irradiation in the liquid phase is shortened.

FIG. 11 shows a cross section of a reactor according to a second embodiment of the present invention. In this embodiment, the shroud 19 has a double cylindrical structure, and the other structure is the same as that shown in FIG. In this embodiment, the feed water is poured into the upper part of the double cylindrical structure annulus portion 36 of the shroud 19 so that the feed water, that is, the reactor water flows through the annulus portion 36 to the lower plenum 7, and the reactor water flows from the upper portion of the annulus portion 36. It uses the heat of the core to heat the reactor water while flowing toward the bottom, and is preheated before the reactor water flows into the core,
The same effect as the first embodiment can be obtained.

FIG. 12 shows a third embodiment of the present invention. A part of the core support plate 20 is provided with a water passage hole 29 for connecting the inner region of the shroud 19 and the lower plenum 7 to the shroud 1.
Baffle plates 28 are provided between the core 9 and the core 1, respectively, and a flow path 37 of reactor water is formed on the inner surface of the shroud 19 from below to above. The flow velocity can be increased by narrowing the distance between the inner surface of the rectifying plate 28 and the shroud 19 as much as possible,
It has the effect of mitigating the corrosive environment. For example, the distance between the inner surface of the shroud 19 and the current plate 28 is 1 cm, and the flow velocity is 10
The flow rate of the reactor water flow path 37 at 0 cm / s is about 50 kg / s in the entire core, which is a level that does not cause a problem in the heat balance of the entire reactor. The straightening vane 28 does not need to completely isolate the reactor water flow path 37 from the core portion, and may be a strip-shaped one to be welded to the upper lattice plate 39 as needed. As shown in FIG. 13, the straightening vanes 28 interfere with the fuel assemblies 32 and the like, and it is difficult to form an integral structure that is continuous over the entire circumference of the core, but between the fuel bundles 32 and the straightening vanes 28. It doesn't matter if there are gaps. Since the current plate 28 itself does not need to support the weight and is not a pressure boundary,
It is not a problem that the corrosive environment on the inner surface of the current plate 28 becomes severe.

FIG. 14 shows the third embodiment, in which the upper part of the shroud 19 is provided with a water passage 3 for communicating the inside and outside of the shroud 19.
4, the pressure outside the shroud is lower than the pressure above the core, so that it is possible to secure a higher flow velocity on the inner surface of the shroud than in the case of the example shown in FIG.

FIG. 15 shows a fourth embodiment of the present invention. In the illustrated fourth embodiment, an upper grid plate connection type internal partition wall 33 is provided around the core 1 to form a descending flow path 38 between the inner wall surface of the shroud 19 and the upper and lower sides of the shroud 19 itself. Water passage holes 34 and 35 are provided to connect the flow path 38 and the downcomer. The operation of the recirculation pump 6 forms a flow from the upper part to the lower part in the downcomer, and the flow of the reactor water in the same direction as in the downcomer is also formed in the flow path as the recirculation pump 6 operates. . In this case, since water having substantially the same water quality as that of the downcomer flows on the inner surface of the shroud 19, the corrosive environment can be expected to be mitigated in both normal operation and hydrogen injection.

[0027]

As described above, according to the present invention, the position at which the reactor water starts to boil moves to the upstream side, and the time during which the reactor water stays in the liquid phase in the core portion and its vicinity becomes shorter. ,
The amount of decomposition products generated by neutron irradiation of water is reduced, and the corrosive environment is mitigated. Similarly, not only can the total amount of radioactive nitrogen generated be reduced, but since neutron irradiation occurs in the region where hydrogen is released into the gas phase, radioactive nitrogen during hydrogen injection is less susceptible to the reducing action, and The upper limit will be significantly higher. Therefore, according to the present invention, the upper limit of the hydrogen injection amount is relaxed, and the hydrogen can be injected as much as practically required, so that the soundness of the structural material of the nuclear reactor is ensured, and the merit in the stable supply of energy is great.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a system diagram showing an example of the overall configuration of a nuclear power plant including a boiling water reactor.

FIG. 3 is a graph showing changes in oxygen concentration in reactor water during hydrogen injection.

FIG. 4 is a graph showing an example of the relationship between the hydrogen concentration in feed water and the relative dose rate of the main steam system.

FIG. 5 is a conceptual diagram showing a mechanism of changing the chemical form of radioactive nitrogen 16.

FIG. 6 is a conceptual diagram showing an analysis result of a corrosive environment in a furnace when hydrogen is injected.

FIG. 7 is a graph showing an example of the distribution of the corrosion potential on the inner peripheral surface of the shroud in the core height direction.

FIG. 8 is a graph showing the hydrogen atom concentration distribution in the height direction of the core in the liquid phase portion of the boiling core during hydrogen injection, with the hydrogen injection amount as a parameter.

9 is a cross-sectional view showing a specific example of installation of the heat pipe shown in FIG.

10 is a cross-sectional view showing another specific example of installation of the heat pipe shown in FIG.

FIG. 11 is a cross-sectional view showing a second embodiment of the present invention.

FIG. 12 is a sectional view showing a third embodiment of the present invention.

FIG. 13 is a plan view showing an arrangement example of the current plate on the inner surface of the shroud of the embodiment shown in FIG.

FIG. 14 is a sectional view showing a modification of the embodiment shown in FIG.

FIG. 15 is a sectional view showing a fourth embodiment of the present invention.

[Explanation of symbols]

1 Reactor core, 2 Upper plenum 3 Steam separator 4 Mixing plenum 5 Downcomer 6 Recirculation pump 7 Lower plenum 8 Reactor cleaning system 9 Water supply-ta 10 Condensate demineralizer 11 Turbin 12 Condenser 13 Hydrogen injection Equipment 14 Water supply pipe 15 Main steam pipe 16A Recirculation pump Suction side pipe 16B Recirculation pump Discharge side pipe 16C Jet pump riser pipe 17 Jet pump 18 Water supply pump 19 Shroud 20 Core support plate 21 Heat pipe group 22 Pressure vessel 23 Fuel rod coating Pipe 24 Fuel pellet 25 Heat pipe 26 Hollow fuel pellet 27 Heat conduction fin 28 Inner partition wall 29 Water passage hole 30 Outer partition wall 31 Jet pump 32 Fuel assembly 33 Upper grid plate connection type inner partition wall 34 Shroud upper water passage hole 35 Shroud lower part passage Water hole 36 Annual Part 37 furnace water flow path 38 downward flow path 39 upper lattice plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Ikeda 7-2-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd.

Claims (13)

[Claims] 1. A core having a heat transfer surface, which is directly connected to a lower portion of a nuclear fuel loading portion of a fuel rod and is arranged on an upstream side of a reactor water flow with respect to the nuclear fuel loading portion of the fuel rod, and a fuel rod channel, A boiling water reactor characterized by comprising one or both of the sections of forced flow of reactor water other than the bypass channel, downcomer, and jet pump. 2. A fuel load which is directly connected to a lower portion of a nuclear fuel loading portion of a fuel rod and is arranged in an upstream region of a reactor water flow with respect to the nuclear fuel loading portion of the fuel rod, in a region inside the pressure vessel contacting the core. Other than the heat transfer surface, fuel rod channels,
A boiling water reactor characterized by comprising either or both of a zone for forced flow of reactor water other than a bypass channel, a downcomer, and a jet pump. 3. A boiling water reactor having a structure having a heating surface other than the fuel loading portion directly connected to the nuclear fuel loading portion of the fuel rod, upstream of the fuel loading portion of the reactor core. 4. A boiling water reactor in which a nuclear fuel for heating reactor water is installed in a nuclear fuel loading portion of a fuel rod, and the reactor water is directly connected to the nuclear fuel loading portion of the fuel rod to heat the reactor water with the heat of the nuclear fuel. A boiling water nuclear reactor comprising a heating means arranged upstream of the fuel loading section. 5. A partition wall forming a downcomer, which is a reactor water flow path, between a pressure vessel, a reactor core mounted in the pressure vessel and loaded with nuclear fuel, and an inner peripheral wall of the pressure vessel that surrounds the core and is disposed around the core. In a boiling water nuclear reactor comprising
A boiling water reactor, wherein the partition walls include a plurality of layers of partition walls arranged concentrically, and an annulus portion formed between the plurality of layers of partition walls forms a reactor water flow path in a vertical direction. 6. A downcomer which is a reactor water flow path between a pressure vessel, a core which is installed in the pressure vessel and in which nuclear fuel is loaded as a fuel assembly, and a reactor water flow passage between an inner peripheral wall of the pressure vessel which is arranged around the core. In the boiling water reactor, the partition wall is formed with a partition wall, and a rectifying plate is provided in the gap between the inner peripheral surface of the partition wall and the fuel assembly, and the partition wall is provided with water passage holes that communicate the front and back sides of the partition wall. A boiling water reactor characterized by: 7. A pressure vessel, a reactor core which is installed in the pressure vessel and is supported by a core support plate, a lower plenum formed below the core support plate, and arranged around the periphery of the reactor core. In a boiling water reactor configured to include a cylindrical shroud forming a downcomer between the pressure vessel and the lower part of the core support plate, a region between the shroud inner peripheral surface and the core is lower. A boiling water reactor characterized by having water passages communicating with the plenum. 8. A boiling water nuclear reactor comprising a heating source below a fuel loading portion of a core. 9. A pressure vessel, a reactor core provided inside the pressure vessel and supported by a core support plate, a lower plenum formed below the core support plate, and a pressure arranged around the reactor core. A cylindrical shroud forming a downcomer with a vessel, and a boiling water reactor in which the reactor core is loaded with a fuel rod cladding tube filled with nuclear fuel, wherein the lower part of the nuclear fuel And a heat transfer means for transferring heat generated by nuclear fission below the nuclear fuel filling portion of the fuel rod cladding tube by using a fluid as a medium, a boiling water nuclear reactor. 10. A fuel rod cladding tube having a pellet-shaped nuclear fuel filled inside, wherein a good thermal conductor is provided at an end of the filled nuclear fuel on the lower side of the core, and heat generated by nuclear fission is transferred to the lower part of the core. A fuel rod cladding tube characterized by being provided with. 11. A fuel rod cladding tube containing nuclear fuel and configured to transfer heat generated by nuclear fission to the outside, wherein the interior of said nuclear fuel is hollow and a good thermal conductor is provided inside thereof. A fuel rod cladding tube comprising means for axially transferring heat generated by nuclear fission to a portion other than the fuel loading portion. 12. A boiling water type in which a fuel rod cladding tube containing nuclear fuel is loaded in a core, and the reactor water is heated by the heat generated by the nuclear fission of the nuclear fuel to generate steam. A boiling water reactor comprising the fuel rod cladding tube according to Item 10 or 11. 13. A boiling water reactor in which nuclear fuel is contained and which heats reactor water with heat generated by nuclear fission of the nuclear fuel to generate steam, and the boiling water reactor connected to the boiling water reactor by a pipeline. The steam turbine driven by the steam generated in the furnace, the condenser attached to the steam turbine to condense and liquefy the steam to generate condensate, and the condensate generated in the condenser In a nuclear power plant comprising a feed water pump that is pressurized and is supplied as feed water to the boiling water reactor, the boiling water reactor is the boiling water according to any one of claims 1 to 9 and 12. Type nuclear reactor characterized by being a nuclear reactor.