JP2001235574A - Reflector control type fast breeder reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen the service life of a reactor core without lengthening the fuel length of a fuel assembly. SOLUTION: This reflector control type fast breeder reactor is provided with a neutron reflector 5 outside of a reactor core 2 submerged in a liquid metal coolant in a reactor vessel 1, and controls the reactivity of the reactor core 2 by moving the reflector 5 vertically to adjust the leakage of neutrons from the reactor core 2. In this case, a combustible poison assembly 19 containing a mixed material of a neutron moderator and a neutron absorber is charged in a center part clearance charged with a large number of fuel assemblies 16, in the reactor core 2. The fast neutrons are thereby moderated by the neutron moderator, and the neutrons are absorbed by the neutron absorber to heighten neutron absorbing capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflector-controlled liquid metal-cooled fast breeder reactor for controlling the reactivity of a reactor core by adjusting the leakage of neutrons from the reactor core by moving a neutron reflector vertically. Hereinafter, referred to as a fast reactor).

[0002]

2. Description of the Related Art An outline of a conventional reflector controlled fast furnace will be described with reference to FIGS. FIG. 5 is a schematic longitudinal sectional view of this type of fast reactor, and FIG. 6 is a transverse sectional view taken along the line AA in FIG. However, FIG. 6 shows a guard vessel 18 not shown in FIG.

[0005] In FIGS. 5 and 6, reference numeral 1 denotes a reactor vessel, and 2 denotes a reactor core installed in the center of the reactor vessel 1.
The core 2 is surrounded by a core barrel 3 on the outside, and includes a large number of fuel assemblies inside, and a neutron absorption channel loaded at the center thereof. A partition wall 4 is disposed outside the core barrel 3 with a predetermined gap.
A neutron reflector 5 and a neutron reflector driving device 6 for driving the neutron reflector 5 are provided in a gap between the neutron reflector 5 and the partition wall 4.

[0004] The gap between the core barrel 3 and the partition wall 4 is a moving area of the neutron reflector 5 used for the operation of the core 2 and also serves as a coolant flow path. A large number of neutron shields 7 are arranged between the partition wall 4 and the reactor vessel 1.

[0005] core 2, core barrel 3, neutron reflector 5,
The partition wall 4 and the neutron shield 7 are installed on a support structure 8. The support structure 8 is provided with a large number of coolant flow holes (not shown), and a lower plenum 9 is provided between the support structure 8 and the reactor vessel 1. Also, the partition 4
Neutron shield 7 placed between the reactor and reactor vessel 1
An intermediate heat exchanger 10 and an electromagnetic pump 11 are provided above and below, and the intermediate heat exchanger 10 has a secondary coolant flow pipe.
12 are installed.

[0006] The upper end opening of the reactor vessel 1 is closed by a shielding plug 13, and the inside of the reactor vessel 1 is filled with a coolant 14 of a liquid metal such as liquid sodium. An upper plenum 15 is provided between the coolant 14 and the shielding plug 13, and the upper plenum 15 is filled with an inert gas.

[0007] The core 2 is a core barrel 3 as shown in FIG.
For example, there are 18 fuel assemblies 16 arranged in a honeycomb shape surrounded by the core barrel 3, and neutron absorption channels 17 loaded at the center of these fuel assemblies 16. The neutron absorption channel 17 is for shutting down the reactor core 2 and is withdrawn upward during operation. In FIG. 6, reference numeral 18 denotes a guard vessel, which is a protective vessel surrounding the reactor vessel 1.

Here, the coolant 14 is circulated by the electromagnetic pump 11 through the inside of the reactor vessel 1 as shown by arrows, and
, And takes out heat from the core 2 and flows out of the core 2. The outflowing coolant 14 exchanges heat with the secondary coolant flowing in the secondary coolant pipe 12 by the intermediate heat exchanger 10.

That is, the coolant 14 flows upward from the inside of the partition wall 4 from below, and flows into the reactor core 2 on the way, taking heat generated by nuclear fission and increasing the temperature. Then, the coolant 14 whose temperature has risen flows into the intermediate heat exchanger 10,
Here, it is cooled by performing heat exchange with the secondary coolant.

The cooled coolant 14 flows downward from the intermediate heat exchanger 10, is pressurized by the electromagnetic pump 11, passes between the partition wall 4 and the reactor vessel 1, and between the neutron shield 7 and the support structure. The material 8 flows down, flows into the lower plenum 9, then goes upward to the lower part of the core 2, and is introduced into the core 2 again.

The neutron shield 7 is for limiting the neutron irradiation dose of the reactor vessel 1 to a predetermined value or less over the entire plant life. The neutron reflector 5 moves up and down in the movement area between the core barrel 3 and the partition 4 with the driving of the neutron reflector driving device 6. This operation adjusts the leakage of neutrons from the core 2 and compensates for the reactivity change due to the combustion of the core 2.

[0012]

However, in a conventional fast breeder reactor in which the reactivity of the core 2 is controlled by moving the neutron reflector 5, the life of the core 2 is extended.
It is necessary to increase the fuel length of the fuel assembly 16. That is, as the combustion proceeds, the reactivity of the fuel assembly 16 becomes negative, and accordingly, the neutron reflector 5 is lifted from the lower part of the core 2 so as to cover the height of the core 2 to increase the neutron reflection ability. It is necessary to increase the positive reactivity of the neutron reflector 5 so that the reactivity of the core 2 as a whole is always 0, that is, an operation in which combustion is continued in a critical state.

For this reason, when trying to extend the driving period,
The fuel length must be increased. If the fuel length is lengthened, the entire length of the reactor vessel 1 is also lengthened, and the economic efficiency deteriorates. There are also problems such as a change in reactivity due to deformation during the life of the reactor core 2 and an increase in pulling force of the fuel assembly 16.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to extend the life of the core only by increasing the initial excess reactivity without increasing the fuel length, thereby improving the economy and fuel efficiency. It is an object of the present invention to provide a fast breeder reactor with a neutron reflector control system having excellent soundness.

[0015]

The invention according to claim 1 is
A neutron reflector is arranged outside the core immersed in the liquid metal coolant in the reactor vessel, and the neutron reflector is moved up and down to adjust the leakage of neutrons from the core so that the neutron leaks from the core. In a reflector-controlled fast breeder reactor for controlling the reactivity, a material obtained by mixing a neutron moderator and a neutron absorber is loaded in the core.

In the present invention, when the reactor starts operation for the first time, that is, when the core reaches criticality, some neutrons in the reactor mix the neutron moderator and the neutron absorber arranged in the core. In a mixed state, for example, a mixture of zirconium hydride and gadolinium.

As the burning of the core progresses, the amount of neutrons generated from the fuel assembly decreases, but gadolinium, which is a mixture of zirconium hydride and gadolinium disposed in the core, also absorbs neutrons and transmutes. So decrease. For this reason, as the core burns, the neutron absorption ability of a substance obtained by mixing zirconium hydride and gadolinium also decreases.

Accordingly, the change in the excess reactivity of the fuel due to the progress of the combustion can be made apparently smaller than in the prior art. In other words, the core life can be extended only by increasing the initial excess reactivity without extending the fuel length in order to extend the core life. Therefore, according to the present invention, it is possible to solve the problems of reduced economy and fuel integrity by the conventional method of extending the fuel length for extending the life of the core, and prolong the life of the core.

According to a second aspect of the present invention, a neutron reflector is disposed outside a core immersed in a liquid metal coolant in a reactor vessel, and the neutron reflector is moved up and down to move the neutron reflector from the core. In a reflector-controlled fast breeder reactor that controls the reactivity of the core by adjusting the leakage of neutrons, a neutron absorber rod containing a substance obtained by mixing a neutron moderator and a neutron absorber, and the neutron absorber rod Are assembled into a plurality of wrapper tubes to form a burnable poisonous aggregate, and the burnable poisonous aggregate is loaded in a central portion of the core.

According to the present invention, neutrons are effectively decelerated by arranging a burnable poison mixed with neutron absorbing material such as gadolinium and zirconium hydride as a neutron moderator in the center of the core, It can be absorbed by a neutron absorbing material to enhance the neutron absorbing ability.

According to a third aspect of the present invention, a neutron reflector is disposed outside a reactor core immersed in a liquid metal coolant in a reactor vessel, and the neutron reflector is moved up and down to move the neutron reflector from the reactor core. In a reflector-controlled fast breeder reactor that controls reactivity of the core by adjusting neutron leakage, a material obtained by mixing a neutron moderator and a neutron absorber is loaded into the upper cavity of the neutron reflector. It is characterized by the following.

According to the present invention, conventionally, the upper part of the neutron reflector is formed as a cavity in order to increase the value of the neutron reflector, but the neutron absorber above the neutron reflector has an additional neutron shielding ability. Thereby, the superstructure can be simplified.

The invention according to claim 4 is characterized in that, when a substance obtained by mixing the neutron moderator and the neutron absorbing material is loaded into the core, the radial distribution of the neutron absorbing rods is made deeper toward the inside. And

According to the present invention, the reduction in the initial thermal neutron absorption effect is reduced, and the reduction in the absorption reactivity is linearly reduced. Thus, the change in the excess reactivity due to the combustion becomes apparently linear, so that the combustion control by driving the reflector can be performed linearly and at a constant speed, thereby facilitating the combustion control.

The invention according to claim 5 is characterized in that the material in which the neutron moderator and the neutron absorber loaded on the neutron reflector are mixed is a material in which graphite and gadolinium are mixed.

According to the present invention, when a material containing a mixture of a neutron moderator and a neutron absorber is loaded into a reactor core, if graphite is used as the neutron moderator, the soundness at high temperatures is excellent and the design margin is increased. In addition, it can sufficiently cope with a case where the coolant outlet temperature is increased.

According to a sixth aspect of the present invention, when the neutron moderator and the neutron absorbing material are mixed into a cladding tube to form a neutron absorbing rod, the neutron moderating material and the neutron absorbing material are granulated. And the granular material is filled in the cladding tube by a vibration filling method.

According to the present invention, the manufacturing process of the neutron moderator-containing neutron absorber is simplified, remote control is facilitated during the manufacturing, and dangerous substances such as when the neutron moderator or the neutron absorber is a radioactive substance. Even if it is present, it becomes easy to manufacture a neutron absorber containing a neutron moderator.

[0029] The invention according to claim 7 is characterized in that a cladding tube or a wrapper tube for containing a substance obtained by mixing the neutron moderator and the neutron absorbing material is provided with an inner lining for preventing permeation of hydrogen. .

According to the present invention, the hydrogen permeation preventing material is lined on the inner surface of the cladding tube or the wrapper tube, so that the hydrogen produced by the combustion of the neutron absorber containing the moderator in the core is not covered by the cladding tube or the wrapper tube. Leakage can be prevented.

According to the present invention, a neutron reflector is disposed outside a core immersed in a liquid metal coolant in a reactor vessel, and the neutron reflector is moved in a vertical direction to move the neutron reflector from the core. In a reflector-controlled fast breeder reactor that controls the reactivity of the core by adjusting the leakage of neutrons, a material in which a neutron moderator and a neutron absorber are mixed in the core, and fission products are mixed. Characterized in that a neutron absorber containing a moderator is disposed.

According to the present invention, by mixing fission products with a neutron absorbing rod, it is possible to effectively utilize fission products contained in radioactive waste generated in another nuclear reactor, It can consume fission products and contribute to weight reduction.

The ninth aspect of the present invention is characterized in that, when the moderator-containing neutron absorber is loaded in the core, the radial distribution of the burnable poison of the neutron absorber is made deeper toward the inside. I do.

According to the present invention, the decrease in the absorption re-concentration due to the combustion of the neutron absorber containing the moderator is made linear, so that the excess reactivity is made apparently linear, so that the necessary neutron reflector is reduced. Control of the driving amount can be facilitated, and combustion control of the core can be facilitated.

The invention according to claim 10 is characterized in that the moderator-containing neutron absorber is provided in a fuel assembly near a central portion in the core. According to the present invention, there is no need to load a burnable poisonous assembly in the center of the core by disposing a neutron absorber rod in which a neutron moderator and a thermal neutron absorber are mixed in the fuel assembly. Therefore, the design of the neutron absorber rod provided in the center of the core becomes easy.

The invention according to claim 11 is characterized in that the neutron absorber containing the moderator is provided in a burnable poisonous aggregate loaded in the center of the core. According to the present invention, since the absorption effect in the region where the neutron energy is small at the end of combustion is reduced, the contribution of fission in the region where the neutron energy is low even at the end of combustion is larger than in the core of a normal fast breeder reactor. For this reason, even in the last stage of the combustion, the shift to the positive reactivity does not become large with respect to the hardening of the spectrum due to the coolant generation void generation, and the void reactivity hardly shifts to the positive side at the end of the combustion, which is advantageous in safety.

The invention according to claim 12 is characterized in that the liquid metal coolant is made of lead or a lead-bismuth alloy. According to the present invention, the use of lead or a lead and bismuth alloy for the coolant further increases the neutron multiplication,
The life of the core can be extended.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a fast breeder reactor according to the present invention will be described with reference to FIGS. 1 (a), 1 (b), 2 and 3. FIG. 1A is a cross-sectional view showing a main part of the fast breeder reactor according to the present embodiment, FIG. 1B is a vertical cross-sectional view of FIG. 1A, and FIG. 3B is a cross-sectional view of the burnable poisonous substance aggregate, and FIG. 3 is a characteristic diagram for explaining the operation of the present embodiment. In FIG. 1A and FIG. Or, portions having similar functions are denoted by the same reference numerals, and description of overlapping portions will be omitted.

This embodiment is different from the conventional example in that FIG.
Instead of the neutron absorption channel 17 loaded in the center of the core 2 shown in FIG. 1, a burnable poison aggregate as shown in FIG.
It has to be loaded with 19. FIG. 1 shows an example in which the present invention is applied to a reflector-controlled sodium-cooled small fast breeder reactor having an equivalent diameter of the core 2 of about 80 cm and an effective length of the core 2 of about 200 cm.

The neutron reflector 5 outside the reactor core 2 is made of graphite or stainless steel (SUS) including a cover gas space.
It has a length of about 200 cm and a thickness of 15 cm. The partition wall 4 is formed on the outer wall of the neutron reflector 5,
The neutron shielding body 7 is on the outside and the reactor vessel 1 is on the outside. At the center of the reactor core 2 is loaded a burnable poisonous aggregate 19 containing, for example, a mixture of zirconium hydride and gadolinium.

As shown in FIG. 2, the burnable poisonous substance aggregate 19 is formed by filling a mixed substance 22 of a neutron moderator and a neutron absorbing material into a cladding tube 21 in a hexagonal tubular wrapper tube 20. The neutron absorber rods 23 are bundled and assembled. The cladding tube 21 is a structural material such as stainless steel, and the mixed substance 22 of the neutron moderator and the neutron absorbing material is, for example, a mixture of zirconium hydride and gadolinium.

Next, the operation of the present embodiment will be described. FIG. 3 shows examples of various reactivity changes during combustion with respect to the final core state of the core of FIG. In FIG. 3, a change a in the combustion reactivity of the fuel assembly 16 and a change b in the value of the neutron reflector 5;
9 shows a change in reactivity c of the burnable poisonous substance aggregate 19. The excess reactivity change of the fuel assembly 16 due to the combustion for 30 years is large, and the initial excess fuel reactivity cannot be canceled only by the change in the value of the neutron reflector 5. If a long-life core having the combustion reactivity shown in FIG. 3 and having a long life of 30 years is constructed only by controlling the neutron reflector 5, the neutron multiplication of the initial core is too large to operate. That is, the initial core configuration greatly exceeds the criticality.

If a burnable poison that absorbs neutrons, such as gadolinium, is inserted into the furnace, the fuel assembly 16
Gadolinium is reduced by the combustion, and the reactivity of the burnable poison is also reduced along with the decrease in the fuel combustion reactivity, and the neutron reflector 5 is controlled by the neutron reflector 5. Along with the change in the reactivity of the fuel and the reactivity of the burnable poison, it is possible to control the combustion for a long life.

In a fast breeder reactor such as the present core, if a substance in which gadolinium as a neutron absorber and zirconium hydride as a neutron moderator are mixed in the reactor, neutrons can be decelerated effectively. Neutron absorption becomes possible.

Next, a second embodiment of the fast breeder reactor according to the present invention will be described with reference to FIG. FIG. 4 shows a main part of this embodiment and corresponds to FIG. 1A.
The same parts as those in (a) are denoted by the same reference numerals, and the description of the overlapping parts will be omitted. This embodiment is different from the first embodiment in that a neutron absorber with a neutron moderator 24 containing a mixed material of a neutron moderator and a neutron absorber is disposed above the neutron reflector 5. is there.

Conventionally, the upper portion of the neutron reflector 5 has a cavity (vacant space) in order to increase the value of the neutron reflector 5, but in the present embodiment, the neutron absorber 24 with a neutron moderator is loaded in this cavity. I do. Thus, in addition to the functions and effects of the first embodiment, a neutron shielding function is provided and the upper structure can be simplified.

Next, a third embodiment of the fast breeder reactor according to the present invention will be described. In the present embodiment, in the first embodiment, when a substance in which a neutron moderator and a neutron absorber are mixed is loaded into the reactor core 2, the radial distribution of the burnable poison as the neutron moderator is made deeper toward the inside. It is in.

The operation and effect of the present embodiment are almost the same as those of the first embodiment, but in addition, the decrease of the initial neutron absorption effect can be reduced, and the reduction of the anti-concentration can be made linear. Therefore, according to the present embodiment, since the reactivity is linear, the change in excess reactivity due to combustion becomes apparently linear, so that the combustion control by driving the neutron reflector 5 can also be performed linearly. The neutron reflector 5 can be driven at a substantially constant speed, and combustion control is facilitated.

Next, a fourth embodiment of the fast breeder reactor according to the present invention will be described. This embodiment is different from the first embodiment in that graphite is used as a neutron moderator when a substance obtained by mixing a neutron moderator and a neutron absorber is loaded into the core 2. According to the present embodiment, it has substantially the same operation and effect as the first embodiment, but also has excellent soundness at high temperatures, increases the design margin, and increases the coolant outlet temperature. Can also respond.

Next, a description will be given of a fifth embodiment of the fast breeder reactor according to the present invention. This embodiment is different from the first embodiment in that a mixed substance 22 of a neutron moderator and a neutron absorbing material is filled into a cladding tube 21 by a vibration filling method as shown in FIG. 23.

That is, when, for example, zirconium hydride and gadolinium are mixed as the mixed substance 22 of the neutron moderator and the neutron absorbing material, both are weighed to a predetermined amount and then formed into granules, and these granules are sealed at the lower end. The stopped covering tube 21 is gradually charged from the upper end opening while being vibrated by a vibrator to be filled. After the vibration filling, a neutron absorber rod 23 is completed by attaching an upper end plug to the upper end opening of the cladding tube 21 and sealing it.
The cladding tube 21 is attached to a vibrating table of a vibrator to apply a predetermined vibration.

According to the present embodiment, the process of forming the neutron absorber rod 23 containing the neutron moderator is simplified, remote control can be performed during the formation, and the neutron moderator or the neutron absorber is a radioactive substance. The neutron absorber rod 23 can be easily formed even with dangerous substances such as cases.

Next, a description will be given of a sixth embodiment of the fast breeder reactor according to the present invention. This embodiment is different from the first embodiment in that a lining, for example, a chromium coating layer for preventing hydrogen permeation is provided on the inner surface of the cladding tube 21 or the wrapper tube 20 shown in FIG. This chromium coating layer is a mixture of neutron moderator and thermal neutron absorber,
For example, it is in contact with a mixture of zirconium hydride and gadolinium.

According to the present embodiment, the burnable poisonous substance aggregate 19 provided with a lining for preventing the permeation of hydrogen is provided by the method shown in FIGS.
By loading the core 2 at the center as shown in (b), it is possible to prevent hydrogen generated by combustion of the core 2 from leaking out of the burnable poisonous aggregates 19. Other functions and effects are the same as those of the first embodiment.

Next, a description will be given of a seventh embodiment of the fast breeder reactor according to the present invention. This embodiment is different from the first embodiment in that a material obtained by mixing a neutron moderator and a neutron absorber, for example, a material obtained by mixing zirconium hydride and fission products (FP) as a neutron absorber is loaded into the core 2. Neutron absorption capacity.

According to the present embodiment, by using fission products (FP) as the neutron absorbing material, radioactive materials generated in other nuclear reactors can be effectively used, thereby contributing to the reduction of fission products. . Other functions and effects are the same as those of the first embodiment.

Next, an eighth embodiment of the fast breeder reactor according to the present invention will be described. In the first embodiment, in the fast breeder reactor using liquid metal as a coolant in the first embodiment, when a material obtained by mixing a neutron moderator and a neutron absorber is loaded into the reactor core 2, the neutron moderator is used. By making the radial distribution of a burnable poison deeper inward,
An object of the present invention is to reduce the decrease in the initial neutron absorption effect and make the reactivity linear, and to make the absorption decrease due to the burning of the neutron absorber with a neutron moderator linear.

According to the present embodiment, it is possible to make the decrease in the excess reactivity linear in appearance, to facilitate the control of the required driving amount of the neutron reflector, and to facilitate the combustion control of the core. .

Next, a ninth embodiment of the fast breeder reactor according to the present invention will be described. In the present embodiment, in the first embodiment, a material obtained by mixing a neutron moderator and a thermal neutron absorber, for example, a material obtained by mixing zirconium hydride and gadolinium is provided in the fuel assembly 16 near the center of the core, The neutron absorption capacity has been enhanced.

According to the present embodiment, by providing a substance in which a neutron moderator and a thermal neutron absorber are mixed in the fuel assembly 16, it is necessary to load the burnable poison assembly 19 in the center of the core. In addition, the design of the neutron absorber rod loaded in the center or the neutron absorption channel 17 shown in FIG. 6 is facilitated.

Next, a tenth embodiment of the fast breeder reactor according to the present invention will be described. In this embodiment, in each of the fast breeder reactors described above, a substance in which a neutron moderator and a neutron absorber are mixed, for example, a substance in which zirconium hydride and gadolinium are mixed is provided in the burnable poison aggregate in the center of the core,
It is to alleviate the transition of the void reactivity toward the positive side at the end of combustion. In the case of the reflector-controlled fast breeder reactor according to the present embodiment, the function is almost the same as in the first embodiment.

In general, in a fast breeder reactor, the void reactivity increases to the positive side as the core burns. This means that in the last stage of combustion, the degree of correct reaction is increased due to spectral hardening when voids are generated.

However, in a fast breeder reactor provided with a neutron absorber rod with a neutron moderator as in this embodiment,
Since the absorption effect in the region where the neutron energy is small in the last stage of combustion decreases, fission contribution in the region where the neutron energy is low even in the last stage of the combustion is larger than that in the core of a normal fast breeder reactor.

For this reason, even at the end of combustion, the shift to the positive reactivity does not become large with respect to the hardening of the spectrum due to the generation of coolant voids. Therefore, it is difficult for the void reactivity to shift to the positive side at the end of combustion, and characteristics excellent in safety are obtained.

Next, an eleventh embodiment of the fast breeder reactor according to the present invention will be described. This embodiment is different from the first embodiment in that lead or a lead-bismuth alloy is used instead of liquid sodium used as a liquid metal coolant. Other configurations are the same as those of the first embodiment.

According to this embodiment, fast neutrons can be decelerated and absorbed by a neutron absorbing material to increase the neutron absorbing ability, and the neutron multiplying property is high and the life of the reactor core can be extended.

[0067]

According to the present invention, it is not necessary to lengthen the fuel length required to extend the life of the core, but only by increasing the initial excess reactivity by increasing the neutron absorption capacity, the core length can be increased. Life can be extended.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing a fast breeder reactor according to a first embodiment of the present invention, and FIG. 1B is a schematic vertical cross-sectional view in FIG.

FIG. 2 is a cross-sectional view showing the burnable poison aggregate in FIGS. 1 (a) and 1 (b).

FIG. 3 is a characteristic diagram for explaining the operation of the fast breeder reactor according to the present invention.

FIG. 4 is a longitudinal sectional view showing a main part of a second embodiment of the fast breeder reactor according to the present invention.

FIG. 5 is a longitudinal sectional view schematically showing a conventional reflector-controlled fast breeder reactor.

FIG. 6 is an enlarged cross-sectional view showing a cross section taken along line AA of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor vessel, 2 ... Core, 3 ... Core barrel, 4 ... Partition wall, 5 ... Neutron reflector, 6 ... Neutron reflector driver, 7
... neutron shield, 8 ... support structure, 9 ... lower plenum, 10 ... intermediate heat exchanger, 11 ... electromagnetic pump, 12 ... secondary coolant piping, 13 ... shield plug, 14 ... coolant, 15 ... upper plenum , 16: fuel assembly, 17: neutron absorption channel, 18: guard vessel, 19: burnable poison assembly, 20 ...
Wrapper tube, 21: cladding tube, 22: mixed substance of neutron moderator and neutron absorber, 23: neutron absorber rod, 24: neutron absorber with neutron moderator, a: change in reactivity of fuel assembly,
b: change in reflector, c: change in burnable poison aggregate.

Claims (12)

[Claims] 1. A neutron reflector is disposed outside a reactor core immersed in a liquid metal coolant in a reactor vessel, and the neutron reflector is moved up and down to adjust neutron leakage from the reactor core. In the fast breeder reactor of the reflector control system that controls the reactivity of the core by the above, the reflector control system characterized in that a material obtained by mixing a neutron moderator and a neutron absorbing material is loaded in the core Fast breeder reactor. 2. A neutron reflector is disposed outside a reactor core immersed in a liquid metal coolant in a reactor vessel, and the neutron reflector is moved up and down to adjust neutron leakage from the reactor core. In the fast breeder reactor of the reflector control system to control the reactivity of the core by doing, a neutron absorber rod containing a substance mixed neutron moderator and neutron absorber,
A reflector controlled fast breeder reactor characterized in that a plurality of the neutron absorber rods are incorporated into a wrapper tube to form a burnable poison aggregate, and the burnable poison aggregate is loaded in a central portion of the core. . 3. A neutron reflector is disposed outside a reactor core immersed in liquid metal coolant in a reactor vessel, and the neutron reflector is moved up and down to adjust neutron leakage from the reactor core. In a fast breeder reactor of a reflector control type for controlling the reactivity of the core by mixing, a material obtained by mixing a neutron moderator and a neutron absorber is loaded in an upper cavity of the neutron reflector. Body controlled fast breeder reactor. 4. The method according to claim 1, wherein a radial distribution of the neutron absorbing rods is increased toward the inside when loading the mixed material of the neutron moderator and the neutron absorbing material into the core. Fast breeder reactor with reflector control system. 5. The reflector control method according to claim 3, wherein the substance in which the neutron moderator and the neutron absorber loaded on the neutron reflector are mixed is a substance in which graphite and gadolinium are mixed. Fast breeder reactor. 6. A neutron moderator and a neutron absorber are formed into granules by filling a clad tube with a substance obtained by mixing the neutron moderator and the neutron absorber, to form a neutron absorber rod. 3. A fast breeder reactor according to claim 2, wherein said cladding is filled in said cladding tube by a vibration filling method. 7. The reflection according to claim 2, wherein a cladding for preventing the permeation of hydrogen is provided on an inner surface of a cladding tube or a wrapper tube for containing a substance obtained by mixing the neutron moderator and the neutron absorbing material. Body controlled fast breeder reactor. 8. A neutron reflector is disposed outside a reactor core immersed in liquid metal coolant in a reactor vessel, and the neutron reflector is moved up and down to adjust neutron leakage from the reactor core. In a reflector-controlled fast breeder reactor that controls the reactivity of the reactor core, a neutron absorber containing a neutron moderator and a neutron absorber mixed in the core, and a moderator-containing neutron absorber formed by mixing fission products A reflector-controlled fast breeder reactor with a body arranged. 9. The method according to claim 8, wherein, when the moderator-containing neutron absorber is loaded into the core, the radial distribution of the burnable poison of the neutron absorber is made deeper toward the inside. Fast breeder reactor with reflector control. 10. The reflector-controlled fast breeder reactor according to claim 1, wherein said moderator-containing neutron absorber is provided in a fuel assembly near a central portion in said reactor core. 11. The reflector-controlled fast breeder reactor according to claim 8, wherein said moderator-containing neutron absorber is provided in a burnable poisonous substance assembly loaded in the center of said reactor core. 12. The liquid metal coolant according to claim 1, wherein the coolant is made of lead or a lead-bismuth alloy.
The fast breeder reactor of the reflector control system described in the above.