JPH0990073A - Liquid-metal cooled fast reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge an output of a nuclear reactor while simplifying a fuel handling structure and shortening a time required for fuel replacement. SOLUTION: While a plurality of in-pile neutron shields 3 are provided in a reactor vessel 2, an integral type fuel assembly in a state of being inserted in a pot 6 is charged in each of the in-pile neutron shields 3 and thereby a plurality of reactor cores are formed. A coolant supply piping 29 is connected to each in-pile neutron shield 3 so as to cool down the inside of each reactor core. In the case of fuel replacement, on the other hand, the integral type fuel assembly in a state of being left immersed in a coolant 8 in the pot 6 is taken out from the reactor vessel 2, together with the pot 6.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid metal cooled fast reactor. More specifically, the present invention relates to a liquid metal cooling furnace capable of increasing the reactor output and capable of rapid fuel exchange.

[0002]

2. Description of the Related Art As a conventional fast reactor, there is a type that loads a large number of rod-shaped fuel assemblies. However, in this fast reactor, refueling cannot be performed quickly because it takes a long time to remove decay heat, and a fuel handling mechanism for refueling, that is, a rotary plug, a fuel exchanger, and This led to an increase in the size of fuel entry and exit planes. On the other hand, when exchanging spent fuel, first insert a pot into the reactor vessel, transfer the rod-shaped fuel assembly to be exchanged to this pot, and dip it into the coolant, and then put the rod-shaped fuel assembly together with the pot into the reactor. Some fast reactors were of the type that they were pulled out of the vessel, but the number of fuel assemblies that had to be exchanged was large, and the fuel exchange work still took time.
Therefore, as an improved liquid metal cooled fast reactor,
As a liquid metal-cooled fast reactor that achieves a high level of simplification of the fuel handling mechanism and rapid refueling work, Japanese Patent Publication No. 7-1
A small liquid metal cooled fast reactor disclosed in Japanese Patent No. 3662 is known. In this small liquid metal cooled fast reactor, an integrated fuel assembly is inserted into a pot, and the integrated fuel assembly is loaded in a single core together with the pot. Then, when exchanging the spent fuel, the integrated fuel assembly is pulled out from the reactor vessel together with the pot while being immersed in the coolant in the pot, and is housed in a sodium cask with a cooling function.

[0003]

However, in the above-mentioned conventional small-sized liquid metal cooled fast reactor, since the integrated fuel assembly is pulled out from the core together with the pot for fuel exchange, the integrated fuel assembly and the pot are Can't be upsized,
Applicable nuclear reactor outputs tens of thousands of kW when generating power
There was a problem that it was limited to a small size of about e. For this reason, it has been difficult to increase the output scale of the reactor while simplifying the fuel handling mechanism and speeding up the fuel exchange work.

[0004]

The present invention is, first of all, to
It is an object of the present invention to provide a liquid metal cooled fast reactor capable of increasing the reactor output by effectively utilizing the generated fast neutrons. Secondly, it is an object of the present invention to provide a liquid metal cooled fast reactor capable of increasing the power output of a nuclear reactor while simplifying the fuel handling structure and shortening the time required for refueling.

In order to achieve the above object, the invention according to claim 1 constitutes a liquid metal cooling fast reactor by providing a plurality of reactor cores in a reactor vessel. Therefore, in this liquid metal cooled fast reactor, the neutron economy is improved, and the output of the entire reactor is improved and the breeding ratio is improved as compared with the total output when each fuel is loaded in different reactors.

According to a second aspect of the present invention, in a liquid metal cooled fast reactor of a type in which an integrated fuel assembly is taken in and out through an opening of a shield plug, a plurality of pot containers are provided in a reactor vessel, and With the integrated fuel assembly inserted in the pot, each pot container is loaded to form a plurality of cores, and cooling system piping is connected to each pot container to cool each core, while fuel exchange is performed. In this case, the integrated fuel assembly is taken out from the reactor vessel together with the pot while the integral fuel assembly is still immersed in the coolant in the pot.

Therefore, the coolant is supplied into each pot housing to which the cooling system pipe is connected. An integrated fuel assembly is loaded in each pot container in a state of being inserted in the pot, and the coolant circulates while cooling the integrated fuel assembly for each pot. Then, at the time of refueling, the integrated fuel assembly together with the pot is taken out of the furnace by lifting the pot from the pot container. At this time,
Since the coolant is accumulated in the pot, the spent fuel is taken out while being immersed in the coolant. Refueling is performed for each pot. Further, as the number of pots installed increases, the amount of fuel loaded increases, and the output of the fast reactor also increases.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on the best mode shown in the drawings.

1 and 2 show an embodiment of a liquid metal cooling fast reactor according to the present invention. The liquid metal cooling fast reactor 1 is of a type in which an integrated fuel assembly is taken in and out through an opening 3a of a shield plug 34 that closes the reactor vessel 2. Note that FIG. 1 shows a case where the present invention is applied to a loop reactor.

The liquid metal cooling fast reactor 1 is provided with an in-reactor neutron shield 3 as a pot container in a reactor vessel 2. The in-core neutron shield 3 is provided at a plurality of locations on the core support structure 4, for example, seven locations. As shown in FIG. 3, each in-core neutron shield 3 is loaded with an integrated fuel assembly 5 described later in a state of being inserted into a pot 6, thereby forming, for example, seven cores. . In the figure, reference numeral 35 is a partition wall that vertically defines the inside of the reactor vessel 2. Each in-core neutron shield 3 is installed below the partition wall 35.

As shown in FIG. 4, the pot 6 is a bottomed cylindrical body having at least a double wall, and a coolant (for example, liquid sodium) is provided between the inner wall and the outer wall forming the reactor core 7. A downward flow path 9 is formed for guiding 8 to the bottom.
Further, at a position near the upper end of the outer wall, there are provided, for example, two coolant inflow holes 21 that open toward the descending flow path 9. The pot 6 is made of, for example, austenitic stainless steel.

Further inside the inner wall of the reactor core 7,
Partition wall 10 for distributing the flow rate of the coolant 8 as needed
Is provided. The partition wall 10 for distribution of flow rate divides the inside of the core tub 7 into an inner region 7a and an outer region 7b, and divides the flow of the coolant 8 into each region 7a, 7b. Further, as shown in FIG. 5, the lower portion of the inner wall of the pot 6 constituting the reactor core 7 is folded back inward, and thereby the folded portion 11 is formed. This folded part 11
Is provided with an appropriate number of inflow holes 14 for introducing the coolant 8 into the outer region 7b. A fuel pin support plate 12 is placed on the folded-back portion 11.

A large number of fuel pins 13 constituting the integrated fuel assembly 5 are fixed to the fuel pin support plate 12 by a tightening means such as a tightening nut, an engaging means such as a flange, or other fixing means. There is. The fuel pin support plate 12 is fitted into a stepped portion 15 formed inside the core tub 7. The fuel pin support plate 12 is constrained in the vertical direction by the stepped portion 15, but is supported so as to be thermally expanded with a gap in the radial direction. Further, the fuel pin support plate 12 is provided with holes 16 for allowing the coolant 8 to flow between the fuel pins 13.

The partition wall 10 is composed of a plurality of cylinders divided in the axial direction and having a certain length. Between the fuel pin support plate 12 and the grid 17, and the grid 1
By adding the partition wall 10 between 7 and the grid 17 above it, the inside of the reactor core 7 can be divided into an inner region 7a and an outer region 7b.

The grid 17 is supported by a large stepped portion 18 formed in the core tub 7 so as to allow thermal expansion in the radial and axial directions. Similar to the fuel pin support plate 12, this grid 17 is also provided with a large number of holes 16 through which the coolant 8 passes. Further, the grid 17 is provided with an annular groove 19 for supporting the partition wall 10 on its lower surface, upper surface or both, and the partition wall 10 is supported by the coolant 8 so as not to move. It should be noted that the leakage of the coolant 8 from the inner region 7a to the outer region 7b may occur at the joint portion between the grid 17 and the partition wall 10, but in the present invention, this is not a significant problem. Further, reference numeral 23 in the drawing is a rectifying cone.
The flow rectifying cone 23 is provided to facilitate the reversal of the flow of the coolant 8.

The opening at the upper end of the pot 6 serves as a discharge port 22. The coolant 8 that has cooled the inside of the pot 6 while flowing through the regions 7a and 7b is discharged from the discharge port 22 to the reactor vessel 2
Spills into. A handling head 20 for refueling is provided at the upper end of the pot 6. The handling head 20 is an engagement portion, for example, a flange, for hooking the gripper claw from the inside when refueling.

The integrated fuel assembly 5 includes a large number of fuel pins 1.
3 For example, about 5000 fuel pins 1
The integrated fuel assembly 5 composed of 3 corresponds to a power generation output of about 50,000 kW. Although not shown in detail in detail, the fuel pin 13 usually contains fuel or the like in a cladding tube and is sealed with end plugs, intermediate plugs or the like, whereby the fuel 24, the shaft blanket 25, the gas plenum 26, and the shield are provided. Body 27,2
It is common to provide regions such as 7 in the pin (cladding pipe). Further, among the fuel pins 13, those located at the peripheral portion of the integrated fuel assembly 5 are, for example, uranium 238.
Blanket fuel with blanket substances such as is inserted.

The fuel pins 13 are normally restrained from each other by the grids 17, ..., 17 having the required number of stages, and are fixed to the reactor core 7. A poison rod region 28 for inserting a poison rod is formed in the central portion of the integrated fuel assembly 5. Although not shown, control rod insertion areas are formed at several locations near the center of the integrated fuel assembly 5. In addition to this, a control region can be provided inside the integrated fuel assembly 5 as required.

Each in-reactor neutron shield 3 is an assembly of rod-shaped neutron shield members, and has a cylindrical shape as a whole. As shown in FIG. 3, an annular groove 3 a is formed on the inner peripheral surface of each in-core neutron shield 3 so as to face the coolant inflow hole 21 of the pot 6. Further, the in-reactor neutron shield 3 is provided with a port 3b that opens toward the annular groove 3a.
Is provided. This port 3b has a cooling system pipe,
Specifically, the coolant supply pipe 29 is connected. The coolant supply pipe 29 is connected to an intermediate heat exchanger (not shown) via an inlet pipe 30 and a primary main circulation pump, and the coolant 8 cooled through the intermediate heat exchanger is stored in the pot 6. Leading to.

A pair of upper and lower sealing members 31, 32 are provided between each in-reactor neutron shield 3 and each pot 6. As shown in detail in FIG. 6, each of the seal members 31 and 32 has, for example, a bellows shape, and the in-core neutron shield 3
It is provided over the entire circumference at both upper and lower positions with the annular groove 3a on the inner peripheral surface thereof sandwiched. That is, each seal member 31, 3
The base end of 2 is fixedly attached to the inner peripheral surface of the pot 6, while the other end thereof is brought into close contact with the outer peripheral surface of the pot 6 with elastic force. Therefore, the coolant 8 flowing from the port 3b into the space inside the annular groove 3a flows into the pot 6 through the space sealed by the seal members 31 and 32. Annular groove 3a
Since the seal members 31 and 32 are provided over the entire circumference of the inner peripheral surface of the in-core neutron shield 3, the orientation of the pot 6 inserted in the in-core neutron shield 3 is either in the circumferential direction. However, in other words, the coolant 8 supplied from the coolant supply pipe 29 is guided into the pot 6 through the coolant inflow hole 21 regardless of the circumferential direction of the coolant inflow hole 21.

Then, the coolant 8 guided into the pot 6
Flows through the descending flow path 7 toward the bottom, then reverses along the rectifying cone 23, flows through the inner region 7a and the outer region 7b of the core core 7, and passes between the integrated fuel assemblies 5. To do. As a result, each fuel pin 13 is cooled. The coolant 8 that has cooled each fuel pin 13 flows out from the discharge port 22 to the periphery of the core upper part mechanism 33, is sucked up from the outlet pipe 36, and is guided to the intermediate heat exchanger, as shown in FIG. 7.
Similarly, the coolant 8 circulates around the seven cores to cool each core.

Each of the sealing members 31 and 32 has a pot 6 for replacing the spent fuel with the reactor neutron shield 3.
When it is pulled out of the pot 6, it is elastically deformed and comes off the pot 6 to allow the pulling out. On the other hand, when the pot 6 is inserted into the in-core neutron shield 3 and fuel is loaded,
Each of the sealing members 31 and 32 is in close contact with the outer peripheral surface of the pot 6 and connects the annular groove 3a and the coolant inflow hole 21 as a series of passages.

As shown in FIG. 2, the seven in-core neutron shields 3 in the reactor vessel 2 surround one in-reactor neutron shield 3 arranged in the center so as to surround another in-reactor neutron shield. Three
Since they are arranged, they can be arranged close to each other, so that the space in the reactor vessel 2 is effectively used.

Table 1 shows the results of trial calculation of electric output and the like when a single core is provided and when seven cores are collected and installed. As is clear from this table, in the fast reactor of the present invention, the amount of fuel loaded is only 7 times, but an electric output of 10 times can be obtained. Also, the breeding ratio and burnup are increased. In this case, the core life is 5 years in each case.

[0025]

[Table 1] In the liquid metal cooling fast reactor 1 configured as described above, the spent fuel is taken out as follows.

First, as shown in FIG. 8, the poison rod 37 is inserted into the poison rod region 28 in the integrated fuel assembly 5 (core) to ensure safety against criticality. Next, as shown in FIG. 9, the core upper part mechanism 33 is pulled out.
After that, as shown in FIG. 10, a dedicated gripper 38 is attached to the pot 6 and the pot 6 is pulled out. The coolant 8 is accumulated in the pot 6, and the integrated fuel assembly 5 is pulled out together with the pot 6 while being immersed in the coolant 8. In this case, the coolant 8 in the pot 6 is the coolant inflow hole 2
The fuel pins 13 are accumulated up to the lower end position of 1, and the top of each fuel pin 13 is immersed in the coolant 8 to ensure the soundness of each fuel pin 13. Then, as shown in FIG. 11, the pulled-out pot 6 is accommodated in a sodium cask 39 with a cooling function waiting in the upper part of the furnace and carried out.

The core upper part mechanism 33 and the pot 6 are
It is pulled out by a crane device (not shown). This crane device is for maintenance of the reactor,
It is a general-purpose machine that is always installed in a nuclear reactor. In the fast reactor 1 of the present invention, since the fuel is exchanged using this crane device, it is possible to eliminate the fuel handling structure, which is a dedicated machine required in the conventional fast reactor. Therefore, the auxiliary equipment can be rationalized, the reactor building can be downsized, and the reactor building cost can be reduced.

In the liquid metal cooled fast reactor 1 of the present invention, it is assumed that refueling will be performed after the decay heat decay waiting time of 2 weeks has passed since the reactor was shut down. Assuming that the temperature of the coolant 8 after the decay heat decay waiting time of 2 weeks is 200 ° C., the temperature of the coolant 8 in the pot 6 after being taken out from the reactor for 1 hour is 370. C., the local maximum temperature of the fuel pin 13 is about 450.degree. In fact, the integrated fuel assembly 5 in the pot 6 taken out of the reactor vessel 2 is immediately accommodated in the sodium cask 39, so that the fuel pin 13 is kept at a lower temperature.

Table 2 shows a liquid metal cooling fast reactor 1 according to the present invention, a conventional liquid metal cooling furnace (a type in which a rod-shaped fuel assembly is pulled out in a state of being inserted in a sodium pot, and an integrated fuel assembly is directly loaded). Type) and decay heat decay waiting time and refueling time. In the liquid metal cooled fast reactor 1 according to the present invention, both decay heat decay waiting time and refueling time are significantly shortened. In Table 2, the evaluation code ◯ means excellent and x means inferior.

[0030]

[Table 2] When the fuel is loaded, the above procedure is reversed to insert the integrated fuel assembly 5 into the in-core neutron shield 3 together with the pot 6.

Next, an embodiment in which the liquid metal cooling fast reactor according to the present invention is applied to a pool type (tank type) fast reactor will be described. As shown in FIGS. 12 and 13, in the reactor vessel 2 of the liquid metal-cooled fast reactor 40, for example, in-reactor neutron shields 3 as pot containers are provided at 7 locations.
Is provided. The coolant 8 for cooling the integrated fuel assembly (not shown) in the pot 6 inserted in each in-core neutron shield 3 is the coolant supply pipe 29 from the primary main circulation pump 41.
Is forced into the port of the in-core neutron shield 3 and then flows into the pot 6 through a pair of upper and lower sealing members that seal between the in-core neutron shield 3 and the pot 6. Then, the coolant 8 flowing into the pot 6 flows out from the pot 6 into the high-pressure plenum 42 above the partition wall 35 after cooling the integrated fuel assembly, and passes through the intermediate heat exchanger 43 to the primary main circulation pump. 41 and is circulated to cool the core. Also in this pool type fast reactor, the spent fuel is exchanged together with the pot 6 as in the loop type fast reactor described above. Further, also in the pool type fast reactor, similar to the loop type fast reactor described above, cores adjacent to each other in the reactor vessel influence each other to improve the neutron economy and increase the electric output. .

In the liquid metal cooling fast reactors 1 and 40 according to the present invention, the reactor vessel 2 can be downsized. Table 3 shows
The liquid metal cooled fast reactor according to the present invention and the conventional fast reactor are compared with the results of trial calculation for electric power of 600,000 kW. In the conventional fast reactor, from the viewpoint of gradually heating the spent fuel, it is necessary to prevent the top of the spent fuel assembly extracted from the core during refueling from being exposed on the coolant free liquid surface in the reactor vessel 2. In order to prevent this, there is a drawback that the height of the reactor vessel 2 becomes large. On the other hand, in the present invention using the integrated fuel assembly 5, since the coolant 8 is secured in the pot 6, the height of the reactor vessel 2 can be greatly reduced. In this case, the height of the reactor vessel 2 can be reduced without increasing the diameter of the reactor vessel 2 as compared with the conventional one.

[0033]

[Table 3] The above-described embodiment is an example of the preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

For example, in the present embodiment, the case where the pots 6 are installed at seven locations in the reactor vessel 2 to form seven cores has been described. However, the number of cores configured by installing the pots 6 is It is needless to say that the number of cores is not limited to seven, and an appropriate number of cores may be provided according to the required reactor power and the like.
In this case, in principle, an arbitrary output can be obtained according to the number of the integrated fuel assemblies 5. However, the upper limit of reactor power is
In addition to the restrictions from the viewpoint of the form of the core and the handling method discussed in the present invention, it also depends on the strength of the reactor structure and the restrictions on manufacturing and implementation. The present invention is for relaxing the former constraint, and is subject to the latter constraint as in the case of the conventional reactor. Therefore, the upper limit of the reactor output in the current technology is approximately 1.2 million kW.
It is considered to be about e.

In this embodiment, the integrated fuel assembly 5 is also used.
Although the fast reactors 1 and 40 of the type in which the reactor is installed in the pot 6 and loaded in the core have been described, the present invention is applied to the fast reactor of the type in which the integrated fuel assembly 5 is directly loaded in the core without using the pot 6. Of course, it is also good.

Further, in the present embodiment, the fast reactors 1 and 40 of the type in which the integrated fuel assembly 5 having the fuel pins 13 formed together is loaded in the core have been described, but the loaded fuel is not necessarily the integrated fuel assembly. It is needless to say that the number is not limited to 5, and may be applied to a fast reactor of a type in which a large number of rod-shaped fuel assemblies are individually loaded in the core.

[0037]

As described above, since the liquid metal cooled fast reactor according to claim 1 has a plurality of cores in the reactor vessel, the neutron economy can be improved and the reactor power can be improved. At the same time, the growth ratio can be improved.

In a liquid metal cooled fast reactor according to a second aspect of the present invention, a plurality of pot accommodating bodies are provided in a reactor vessel, and an integrated fuel assembly is inserted into each of the pot accommodating bodies. To form a plurality of cores, and a cooling system pipe is connected to each of the pot housings to cool the inside of each of the cores, so that the amount of fuel to be loaded can be increased by increasing the number of pots to be installed. . Therefore, it is possible to easily increase the output of the nuclear reactor.

When the fuel is exchanged, the integrated fuel assembly is taken out of the reactor vessel together with the pot in a state where the integrated fuel assembly is immersed in the coolant in the pot.
After shutting down the reactor, refueling can be started when the decay heat is removed to some extent. Therefore, the refueling work can be started early, the decay heat decay waiting time can be significantly shortened, and the operating rate of the nuclear power plant can be improved. Further, since the fuel exchange work becomes simple, the time required for the exchange work itself can be shortened, and the operating rate of the nuclear power plant can be further improved.

Further, by using the integral fuel assembly, it becomes possible to perform refueling using the crane device installed in the furnace. For this reason, the fuel exchanger, which was required in the conventional fast reactor, becomes unnecessary, the construction cost of the fast reactor can be suppressed, and the power generation cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a liquid metal cooling fast reactor according to the present invention and schematically showing the configuration when applied to a loop reactor.

FIG. 2 is a plan view showing a layout of a core of the liquid metal cooled fast reactor of FIG. 1 in plan view.

FIG. 3 is a cross-sectional view showing a main part of the liquid metal cooling fast reactor of FIG.

FIG. 4 is a cross-sectional view showing in detail a pot of the liquid metal cooled fast reactor of FIG.

5 is an enlarged sectional view of a part of the pot of FIG.

6 is a schematic configuration diagram showing a seal structure between an in-core neutron shield and a pot of the liquid metal cooled fast reactor of FIG.

7 is a cross-sectional view of the liquid metal cooled fast reactor along the arrow VII-VII in FIG.

FIG. 8 is a diagram showing a procedure for refueling the liquid metal cooled fast reactor of FIG. 1.

FIG. 9 is a diagram showing a procedure for refueling following FIG.

FIG. 10 is a diagram showing a procedure for refueling following FIG.

11 is a diagram showing a procedure for refueling following FIG.

FIG. 12 is a cross-sectional view schematically showing another embodiment of a liquid metal cooling fast reactor according to the present invention and showing a configuration when applied to a pool reactor.

FIG. 13 is a plan view showing a layout of a core of the liquid metal cooled fast reactor of FIG. 12 in plan view.

[Explanation of symbols]

 1,40 Liquid metal cooled fast reactor 2 Reactor vessel 3 In-core neutron shield (pot container) 5 Integrated fuel assembly 6 Pot 8 Coolant 29 Coolant supply pipe (cooling system pipe) 34 Shield plug 34a Opening

Claims (2)

[Claims] 1. A liquid metal cooling fast reactor comprising a plurality of reactor cores in a reactor vessel. 2. A liquid metal cooled fast reactor of the type in which an integrated fuel assembly is taken in and out through an opening of a shielding plug,
A plurality of pot accommodating bodies are provided in the reactor vessel, and a plurality of cores are formed by loading the integrated fuel assemblies into the pot accommodating bodies while being inserted into the pots to form a plurality of cores, and cooling to the pot accommodating bodies When the system cores are connected to cool the respective cores, respectively, while the fuel is exchanged, the reactors together with the integrated fuel assembly are immersed in the coolant in the pots. A liquid metal cooled fast reactor characterized by being taken out from a container.