JPH07146390A - Reactor core and fuel inserts - Google Patents

Abstract

(57) [Abstract] [Purpose] By reducing the neutron irradiation dose in the pressure vessel without increasing the output peaking coefficient in the system direction and without shortening the operating period due to neutron absorption, To obtain a reactor core and a fuel insert capable of extending the life. A core comprising a fuel assembly loaded on the outermost periphery of a nuclear reactor core and a fuel insert comprising a neutron absorbing member for limiting neutron irradiation to a core vessel, and the fuel insert.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor core and a fuel insert which can prolong the life of a reactor pressure vessel.

[0002]

2. Description of the Related Art The life of a reactor pressure vessel is shortened due to embrittlement due to irradiation of neutrons leaking from the core. For this reason, as a conventional measure for reducing the irradiation of the pressure vessel, a low-leakage loading pattern in which fuel with low reactivity (high burnup) is loaded on the outermost periphery of the core is adopted.

[0003]

However, since the output of the entire outer peripheral fuel is low, the output of the central portion is high and the output peaking exceeds the limit value or the margin for the limit value is reduced. .

The present invention reduces the neutron irradiation dose of the pressure vessel without increasing the output peaking coefficient in the system direction and without shortening the operation period due to neutron absorption, thereby extending the life of the reactor pressure vessel. The purpose of the present invention is to obtain a reactor core and a fuel insert that can be lengthened.

[0005]

In the nuclear reactor core according to the present invention as set forth in claim 1, neutrons for limiting neutron irradiation to a core vessel of a fuel assembly loaded on the outermost periphery of the nuclear reactor core are provided. The fuel insert is composed of an absorbing member.

In the fuel insert according to the second aspect of the present invention, the fuel insert loaded in the fuel assembly is loaded in the fuel assembly loaded on the outermost periphery of the reactor core. In this case, a non-flammable neutron absorbing member for limiting neutron irradiation to the core vessel is arranged in the control rod guide tube located on the inner wall surface of the core vessel.

Further, in the fuel insert according to the invention described in claim 3, in the fuel insert according to claim 2, the neutron absorbing member is a rod-shaped body containing hafnium (Hf). .

Further, in the fuel insert according to the invention described in claim 4, in the fuel insert according to claim 2, the neutron absorbing member is a rod-shaped body containing Inconel.

[0009]

According to the present invention, the fuel assembly loaded on the outermost periphery of the reactor core is loaded with the fuel insert made of the neutron absorbing member for limiting the neutron irradiation to the core vessel. Therefore, the side where the neutron absorbing member is arranged, that is, the output of only the part from the core inner wall surface can be reduced, and the neutron irradiation amount to the pressure vessel can be reduced, and the life of the reactor pressure vessel can be lengthened. You can

That is, the life of the reactor core vessel is shortened due to embrittlement due to irradiation of neutrons leaking from the core,
In the fuel assembly loaded in the outermost periphery of the core, that is, in the vicinity of the surface in contact with the outer periphery of the core, by loading a fuel insert consisting of a neutron absorbing member for limiting neutron irradiation to the core vessel It is possible to reduce the amount of neutron irradiation to the core vessel without making any special changes to the conventional core design, etc., and to prolong the life of the reactor core vessel.

In the present invention, the fuel assembly loaded on the outermost periphery of the reactor core is loaded with a fuel insert made of a neutron absorbing member for limiting neutron irradiation to the core vessel. Any type of reactor can be used as long as it is a pressurized water type or boiling water type reactor.

Specifically, in a pressurized water reactor, a non-combustible neutron absorbing material is used in the same manner as a fuel insert such as a combustible poison rod loaded in a control rod guide tube of a fuel assembly. It is possible to load and use the fuel insert, which is made of the absorption rod made by, in the control rod guide tube. Therefore, the conventional fuel assembly can be used as it is, the neutron irradiation dose to the pressure vessel can be reduced without requiring any special modification to the fuel assembly, and the life of the reactor pressure vessel can be extended. be able to.

As a concrete neutron absorbing material, a substance capable of absorbing neutrons well can be used.
More preferably, an absorbing member made of a non-combustible neutron absorber can be used. For example, a metal or alloy / compound such as Cd, Hf, or Inconel having a large neutron absorption cross section can be used.

Therefore, the conventional reactor core and fuel assembly can be used as they are without any change,
The neutron irradiation dose to the pressure vessel can be reduced without requiring any special modification to the reactor core or fuel assembly, and the life of the reactor pressure vessel can be extended.

Further preferably, the neutron absorbing member is hafnium (Hf) or Inconel (Inconel).
Nel) -containing rods can be used. Generally, the burnable poison rod of the fuel insert of the burnable poison can be replaced with the rod-shaped body of the neutron absorbing member. That is, in the fuel assembly, non-flammable neutron absorption for limiting neutron irradiation to the core vessel in the control rod guide tube located from the inner wall surface of the core vessel when loaded in the outermost periphery of the reactor core A member, for example, a fuel insert having a rod-shaped body containing hafnium (Hf) or Inconel can be loaded and used.

Therefore, since the absorption rod containing hafnium (Hf) is loaded only on the outermost peripheral portion of the core having a low output, the influence on the core reactivity is reduced without shortening the operation period due to neutron absorption, and the pressure vessel Can reduce the neutron absorption of.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing the construction of an embodiment of a fuel insert of the present invention to be inserted into a control rod guide tube of a fuel assembly, FIG. A being a plan view and FIG. is there. FIG. 2 is an explanatory view showing the structure of a pressurized water reactor fuel assembly in which the fuel insert of FIG. 1 is loaded. FIG. 3 is an array diagram of absorption rods of the fuel insert of FIG. FIG. 4 is an array diagram showing the arrangement of fuel assemblies in the reactor core.

As shown in FIG. 2, the fuel rod 11 is attached to the support grid 1.
There is a fuel assembly 10 which is bundled in the form of a bundle in 2, and a part of the fuel rod 11 is replaced by a control rod guide pipe 15 connecting the upper nozzle 13 and the lower nozzle 14. The fuel insert 20 shown in FIG. 1 is inserted into the control rod guide tube 15.

In the fuel insert 20 of FIG. 1, absorption rods 21 made of several neutron absorbers are inserted corresponding to the respective positions of the control rod guide tube 15 of FIG. A zircaloy rod 22 and a thimble plug 23 are suspended.
Specific examples of the absorbing rod 21 include hafnium (Hf) coated with a stainless steel pipe or Inconel (Inconel).
a solid rod made of Nel) is used.

Specific arrangements of the absorbing rods 21 in the fuel insert 20 include A type shown in FIG. 3A, and
There is type B shown in Figure b. That is, the A type is shown in FIG.
Absorbing rod 2 for the fuel insert in the fuel assembly mounted at the corner of the outermost fuel assembly of the pressurized water reactor core shown in FIG.
1 is an arrangement pattern. Type B is the arrangement pattern of the absorption rods 21 of the fuel inserts in the fuel assembly mounted on the side of the outermost fuel assembly of the pressurized water reactor core shown in FIG.

As shown in FIG. 3a, the absorption rod 21 is L
It is arranged in a letter shape. This fuel assembly 10a is shown in FIG.
As shown in FIG. 5, the L-shaped corners are loaded in the core so that the corners of the core match the corners of the core. Further, as shown in Fig. B, the absorption rod 21 is arranged along one side of the fuel assembly 10b. This fuel assembly 10b is one in which the absorption rods 21 are loaded inside the core along the sides of the core.

Therefore, as shown in FIG. 4, the absorbing rod 21 is arranged so as to surround the reactor core. Therefore, since the solid rod of the neutron absorber is arranged closer to the outer periphery of the core, the neutron irradiation charge of the pressure vessel outside the core can be reduced. In FIG. 4, 10 ′ indicates a fuel assembly into which the control rod cluster is inserted, and indicates a fuel assembly into which an insert such as the absorption rod 21 cannot be inserted.

Further, since the absorbing rod 21 is made of Hf coated with a stainless steel pipe or a solid rod made of Inconel, it is less damaged by neutron absorption. Therefore, it has a long life and can be reinserted into the fuel assembly arranged in the outermost periphery and used again after the next cycle.

Further, the solid zircaloy rod 22 which is used as the non-absorbing rod other than the absorbing rod 21 mounted on the fuel insert 20 in the same manner as the single plug 23 is long, and the absorbing rod 21 is a long rod.
It is preferable to suspend the object from the above because of the weight balance when handling the suspended insert.

As described above, since the absorption rod 21 is thinly arranged so as to surround the reactor core, the peak output coefficient in the system direction is not increased, and the operation period due to neutron absorption is not shortened. The absorption amount is 70-
It can be reduced to 30%. In addition, the output of only the portion of the fuel assembly loaded on the outermost peripheral portion of the core with low output from the inner wall surface of the core container (only the side where the absorbing rod is arranged) is reduced, so In the conventional case of loading the reactivity fuel, the output of the entire fuel assembly is low, but the output increase in the central portion is small.

Further, since the absorption rod 21 containing non-combustible hafnium (Hf) or Inconel is used as the neutron absorbing member of the fuel insert, the loss due to neutron absorption is small and the operating period due to neutron absorption is short. Therefore, the influence on the core reactivity can be reduced and the neutron absorption amount of the pressure vessel can be reduced. Further, since the absorbing rods are loaded only on the outermost peripheral portion of the core having a low output, the influence on the core reactivity is small.

[0027]

As described above, according to the present invention, the fuel assembly loaded on the outermost periphery of the nuclear reactor core is loaded with the fuel insert made of the neutron absorbing member for limiting the neutron irradiation to the core vessel. Therefore, in particular, a neutron absorbing member for limiting neutron irradiation to the core vessel is arranged in the fuel assembly loaded in the outermost periphery of the core, that is, in the vicinity of the surface in contact with the outer periphery of the core. As a result, the neutron irradiation dose to the core vessel can be reduced and the life of the reactor core vessel can be extended without making any special changes to the conventional core design or the like.

Further, in a pressurized water reactor, as with fuel inserts such as combustible poison rods and fuel clusters loaded in the control rod guide tubes of the fuel assembly, it is made of non-combustible neutron absorbing material. The neutron absorbing member can be used by loading the neutron absorbing member into a control rod guide tube as a fuel insert including an absorbing rod.
Therefore, the conventional one can be used as it is, the neutron irradiation dose to the pressure vessel can be reduced without requiring any special change in the fuel assembly, and the life of the reactor pressure vessel can be extended. it can.

As a concrete neutron absorbing material, an absorbing member made of a non-combustible neutron absorbing material can be used. More preferably, the neutron absorbing member is hafnium (Hf) or Inconel (Inconel).
It is possible to use a rod-shaped body containing 1).

Therefore, since the absorption rod containing hafnium (Hf) is loaded only on the outermost peripheral portion of the core having a low output, the influence on the core reactivity is reduced without shortening the operation period due to neutron absorption, and the pressure vessel There is an effect that the neutron absorption amount of can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration of an embodiment of a fuel insert of the present invention to be inserted into a control rod guide tube of a fuel assembly, and FIG.
Is a plan view and FIG. B is a side view.

FIG. 2 is an explanatory view showing a configuration of a pressurized water reactor fuel assembly in which the fuel insert of FIG. 1 is loaded.

FIG. 3 is an array diagram of absorption rods of the fuel insert of FIG.
The figure shows the arrangement of A type and the b figure shows the arrangement of B type absorbing rods.

FIG. 4 is an array diagram showing an arrangement of fuel assemblies in a nuclear reactor core according to an embodiment of the present invention.

[Explanation of symbols]

 10, 10a, 10b ... Fuel assembly, 11 ... Fuel rod, 12 ... Support grid, 13 ... Upper nozzle, 14 ... Lower nozzle, 15 ... Control rod guide tube, 20 ... Fuel insert, 21 ... Absorption rod, 22 … Solid Zircaloy sticks, 23… Thimble plugs,

Claims (4)

[Claims] 1. An atom characterized in that a fuel assembly loaded on the outermost periphery of a nuclear reactor core is loaded with a fuel insert made of a neutron absorbing member for limiting neutron irradiation to a core vessel. Reactor core. 2. A fuel insert inserted into a fuel assembly, wherein the control rod guide pipe is located closer to an inner wall surface of the reactor core when the fuel assembly is loaded on the outermost periphery of the reactor core. A fuel insert, comprising a non-flammable neutron absorbing member for limiting neutron irradiation to the core vessel. 3. The fuel insert according to claim 2, wherein the neutron absorbing member is a rod-shaped body containing hafnium (Hf). 4. The fuel insert according to claim 2, wherein the neutron absorbing member is a rod-shaped body containing Inconel.