JPH079472B2 - Small liquid metal cooled fast reactor - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a relatively small fast reactor having an electric output of 100 MWe class or less.

[Prior art]

The core of a conventional reactor is constructed by collecting a large number of fuel assemblies and reflectors. The conventional furnace is equipped with a rotary plug, a fuel exchanger and a fuel inlet / outlet.The spent fuel assembly is temporarily transferred to the relay tank in the reactor by the mutual movement of the rotary plug and the fuel exchanger, and further It is designed to be taken out of the furnace from the relay tank inside the furnace. Even in the case of a relatively small liquid metal-cooled fast reactor with an electric output of 100 MWe or less, if the method of taking out the spent fuel assembly in the large-scale fast reactor described above is scaled down and adopted, a fuel exchanger or a rotary plug will be used. However, even if the reactor output is small and the core is downsized, the current structure cannot be downsized, resulting in a large amount of power and poor economic efficiency. In order to solve such a problem, the applicant has fixed a large number of fuel pins with a grid of a plurality of stages and encloses them with an outer cylinder which is a fuel assembly duct, and arranges the fuel pins in a plurality of regions in the outer cylinder. A patent application was filed for an integrated fuel assembly in which a partition wall is provided (Japanese Patent Application No. 1-28422). If this integrated fuel assembly can be put in and taken out from the center plug at the upper part of the furnace, the conventional rotary plug, fuel exchanger, fuel inlet and outlet can be omitted, and it is suitable for a relatively small liquid metal cooled fast reactor. It is disclosed.

[Problems to be Solved by the Invention]

However, the above-mentioned contents of the application do not disclose the specifics of what to do only to put the fuel assembly in and out from the center plug for the fuel exchange. The present invention relates to a liquid metal cooling fast reactor of a type in which an integrated fuel assembly is put in and taken out from a center plug at the upper part of the furnace,
It is an object of the present invention to provide a reactor structure capable of safely performing fuel refueling work by shortening a reactor downtime for refueling.

[Means for Solving the Problems]

According to the present invention, a fuel transfer pot that can be inserted into and taken out from the center plug and into which the fuel assembly is inserted and loaded is provided inside, and the coolant flows into the lower surfaces of the fuel assembly duct and the fuel transfer pot of the fuel assembly. A hole is formed and a means for opening and closing the coolant inflow hole is provided to connect and disconnect the two coolant inflow holes. The opening / closing means of the coolant inflow hole can be configured by a concave-convex engagement mechanism provided on the fuel assembly duct side and the fuel transfer pot side. Preferably, a poison rod insertion pipe is erected at the center of the fuel assembly duct so that the poison rod can be inserted into the poison rod insertion pipe from outside the furnace.

[Work]

By the opening / closing means of the coolant inflow hole, the fuel assembly duct of the fuel assembly and the respective coolant inflow holes of the fuel transfer pot for accommodating the fuel assembly duct inside are brought into communication with each other, whereby the fuel transfer pot is It can be operated by leaving it in the furnace. By switching the opening and closing means of the coolant inflow hole to shut off both coolant inflow holes, if the fuel transfer pot is lifted straight, the spent fuel assembly in the fuel transfer pot is dipped in the pumped coolant. Can be taken out of the furnace in the state of being kept. If the poison rod is inserted from the outside of the furnace into the poison rod insertion pipe erected in the center of the fuel transfer pot, the safety at the time of refueling is enhanced.

【Example】

As an embodiment of the present invention, FIG.
Figure shows the case of pool type. The pool type in Figure 2 is the first
Instead of providing the inlet pipe 2 and the outlet pipe 3 in the reactor vessel 1 unlike the loop type shown in the figure, the intermediate heat exchanger 4 and the primary main circulation pump 5 are installed in the reactor vessel 1. However, the others are the same. In either case, the upper portion of the reactor vessel 1 which is a cylindrical vertical vessel made of stainless steel has a shield plug 6, a control rod drive mechanism 7 outside the reactor, and a control rod guide tube 8 inside the reactor. It is covered with a mechanism 9 and a center plug 10 tightly plugged with a poison rod plug 11. Inside the reactor vessel 1, a core support 12 is provided below the core support 12.
A radial reflector 13 is fixed on top of the. Radial reflector
Inside the 13 is provided a control rod absorber 14 which can be moved up and down by being driven by the control rod drive mechanism 7 installed above the core upper mechanism 9. Inside the control rod absorber 14, the fuel transfer pot 15 is mounted with the core support 12 described above. Its fuel transfer pot
Inside the core 15, a fuel assembly duct 16 and a fuel assembly 18 formed by bundling a number of fuel pins 17 inside the duct are inserted and loaded to form a core. As shown in FIG. 3, the fuel assembly duct 16 has a coolant inflow hole 19 formed in the lower surface of a bottomed cylindrical body having an open upper end,
The convex portion 20 is provided on the side surface, and the handling head 21 is formed on the inner surface of the upper end of the duct. Further, a poison rod insertion pipe 22 is provided upright at the center of the inside of the fuel assembly duct 16 so that an inflow hole 26 is opened downward so that a coolant can enter the pipe. Also in the illustrated example, a partition 23 that divides the core into two regions is provided, and a flow distribution orifice 24 that optimally distributes the flow for each region is bored, and a grid 25 of several stages is arranged in the axial direction. This is the same as the above-mentioned application in that a large number of fuel pins 17 are fixed by these grids 25. Incidentally, in FIG. 3, two fuel pins 17 are provided in the inner region,
Although only two are shown in the outer area, it is about 10,000 in the 100 MW class electric output. Fuel transfer pot 13 with fuel assembly duct 16 fitted inside
Fig. 4A shows the shape of the fuel cell and its relationship with the fuel assembly duct 15.
And B. The fuel transfer pot 13 includes a fuel assembly duct 16
Similarly to the above, a bottomed cylindrical body having an open upper end is formed. A coolant inflow hole 27 is formed in the bottom surface of the fuel transfer pot 13. In the longitudinal direction of the inner surface of the pot, there are two concave grooves 28, 28 engageable with the convex portion 20 formed on the outer surface of the fuel assembly duct 16 described above.
It is formed in places. At the upper end of the pot, although not shown, a handling head similar to the handling head 21 of the fuel assembly duct 16 is provided and can be hung by a gripper, or a hook is provided and hung by a wire. . The convex portion 20 of the fuel assembly duct 16 and the two recessed grooves 28 of the fuel transfer pot 13 connect and block the communication of the coolant inlet holes 19 and 27 formed on the lower surfaces of the fuel assembly duct 16 and the fuel transfer pot 13, respectively. The opening / closing means of the coolant inflow hole for performing the above. The embodiment of FIG. 4A in which the convex portion 20 fits into the one concave groove 28 is the coolant inlet hole 27 of the fuel transfer pot 13 and the fuel assembly duct 16.
This is the state of the "operation mode" in which the coolant inflow holes 19 of the above are matched and the coolant can be passed through the core. The mode of FIG. 4B in which the other groove 24 is engaged is in the “fuel exchange mode” state in which both the coolant inflow holes 19 and 27 are closed. The piercing action in the "refuel mode" condition must be reliable. If the opening action is uncertain, the coolant pumped up by lifting the fuel transfer pot 13 may flow out from the coolant inlet holes 19, 27. To change the "operation mode" (communication of both coolant inflow holes) and "fuel exchange mode" (close both coolant inflow holes) by the above-mentioned means for opening and closing the coolant inflow hole, the fuel assembly duct
The convex portion 20 is moved by the vertical movement of 16 and the rotation in the horizontal plane.
It is possible by replacing. More specifically, with the fuel transfer pot 13 in the state of its side, the claws of the gripper shaft 31 (see FIG. 5E) inserted into the furnace from the upper part of the furnace are connected to the fuel assembly duct 16 by the claws of the gripper. After engaging and locking the handling head 21 and pulling out only the fuel assembly duct 11 into the coolant of the reactor upper plenum, after rotating it by the phase angle of the two convex grooves 28, 28, another Groove
Engage with 24 and lower. The liquid level of the coolant free liquid surface 29 is set so that the above replacement can be performed in the coolant in the reactor vessel 1. In the example of the convex-concave engaging mechanism of the convex portion 20 and the two convex groove 28, 28, the convex portion 20 is provided on the side surface of the fuel assembly duct 16 so as to project.
Two concave grooves 28 are formed on the inner surface of the fuel transfer pot 13,
The relationship may be reversed, or the bottom surface may be used instead of the side surface. The entire procedure for removing spent fuel from this reactor is shown in Figure 5A.
~ It demonstrates by FIG. 5H. It has been running continuously for about 3 years,
The decay heat is about 0.2% of the rated output when two weeks have passed (waiting for decay heat decay) after the reactor shutdown. Since FIG. 5A showing this state is in the "operation mode", in order to change to the "fuel exchange mode", the poison rod plug 11 is first removed from the hole formed as shown in FIG. 5B. Poison rod insertion tube in the core by suspending rod 30
Fit in 22. The poison rod 30 is similar to the control rod absorber 12 and is for holding the core subcritical when moving the fuel assembly 18 through the coolant in the reactor.
Next, as shown in FIG. 5C, the control absorber 14 is pulled out leaving the control absorber 14 in the furnace, and then the center plug 11 is removed as shown in FIG. 5D, and the gripper is removed as shown in FIG. 5E. The shaft 31 attached is lowered to lift the fuel assembly duct 16 described above,
Rotate and suspend to change to "fuel change mode". In this way, the extraction preparation work is completed, and the process is as shown in FIG. 5F. Next, as shown in FIG. 5G, the fuel transfer pot 15 is lifted to be pulled out together with the fuel assembly 18. At this time, the fuel transfer pot 15 is filled with the pumped coolant. The fuel transfer pot 15 and the fuel assembly 18 taken out to the upper part of the furnace are put in the transfer cask 32 as they are and carried out as shown in FIG. 5H. It has been confirmed that the maximum temperature of fuel pellets when taken out two weeks after the reactor shutdown is 450 ° C or lower. 6A to 6H show the procedure for loading new fuel. Normally, the upper core mechanism 9 does not need to be pulled out at the time of refueling except for inspection and replacement of the upper reactor instrumentation. But,
In FIG. 6A showing the state before loading with new fuel, the core upper part mechanism 9 is removed for easy understanding. Prior to the new fuel loading, the core upper part mechanism 9 and the control rod absorber 12 are inserted as shown in FIG. 6B, and then the fuel assembly 18 (which is stored in the fuel transfer pot 15 as shown in FIG. 6C ( The poison rod 30 has been inserted), and the upper core mechanism 9 is guided to load the core. At that time, it is in the "operation mode" state. When the loading is completed, the center plug 10 is attached to the core upper part mechanism 9 as shown in FIG. 6D, and the control rod drive mechanism 7 is further attached as shown in FIG. 6E to connect with the already inserted control rod absorber 12. To do. Then, pull out the poison rod 30 as shown in FIG. 6F, and after pulling out, attach the poison rod plug 11 as shown in FIG. 6G, and then pull out the control rod absorber 14 as shown in FIG. 6H and pull out the reactor. To start. Since the refueling work is as described above, it will be completed within 1 to 2 days. On the other hand, the conventional type requires about 10 days, and the present invention makes it possible to greatly shorten the period. Further, when comparing the amount of the reactor structure, the conventional type has about 1700 tons, but the present invention has about 700 tons, which is a great reduction. Incidentally, FIGS. 7A to 7C show on the same scale a design example of a conventional fast reactor loop type, a loop type and a pool type of the present invention for a small fast reactor having an electric output of 100 MW class. Comparing the two, it is obvious that the simplification and miniaturization of the device are remarkable in the case of the present invention. In addition, 33 is a rotary plug, 34 is a fuel exchanger, 35 is a fuel inlet / outlet machine, and 36 is a relay tank in the reactor.

[Effect of the invention]

As described above, according to the present invention, the fuel transfer pot for accommodating the fuel assembly duct of the fuel assembly inside has a simple structure of a bottomed cylindrical body, and mounting the same does not require a large area. Then, even if the fuel transfer pot is put in and out of the furnace in the "operating mode" by the opening / closing means of the coolant inlet hole, it does not cause any trouble including the flow of the coolant, and the loading place of the fuel assembly is not changed. Since it is possible to provide a portion corresponding to the conventional relay tank in the reactor, it is not necessary to enlarge the reactor vessel. Moreover, the used fuel assemblies can be taken out together with the fuel transfer pot in a state of being immersed in the coolant, by switching to the "fuel extraction mode" and lifting the fuel transfer pot straight. This not only shortens the time required for refueling, but also sufficiently guarantees safety. If the opening / closing means of the coolant inlet / outlet is a concave / convex engagement mechanism provided on the fuel assembly duct side and the fuel transfer pot side, the structure is simple, and the fuel assembly duct moves vertically and rotates in the horizontal plane. It is possible to switch between the "operating mode" in which both coolant inflow holes communicate with each other and the "fuel exchange mode" in which both coolant inflow holes are shut off because it can be switched relatively easily and in a short time. When the poison rod is inserted from the outside of the furnace into the poison rod insertion pipe erected in the center of the fuel transfer pot, the safety during refueling is further enhanced.

[Brief description of drawings]

FIG. 1 shows an embodiment in which the present invention is applied to a loop reactor.
FIG. 2 is an embodiment in which the present invention is applied to a pool-type reactor, FIG. 3 is a longitudinal sectional view and a central transverse sectional view of a fuel assembly, and FIG. 4A is a fuel in an “operation mode” state. FIG. 4B is a longitudinal sectional view showing the relationship between the assembly and the fuel transfer pot, and a central transverse sectional view; FIG. 4B is a vertical sectional view showing the relationship between the fuel assembly and the fuel transfer pot in the “fuel exchange mode” state 5A to 5H are explanatory views showing a procedure for taking out spent fuel, and FIGS. 6A to 6H are explanatory views showing a procedure for loading new fuel, and FIG.
FIGS. A to C show, on the same scale, design examples of the conventional reactor loop type, the loop type and the pool type of the present invention, for a small fast reactor with an electric output of 100 MW class. 1 ... Reactor vessel, 6 ... Shielding plug, 7 ... Control rod drive mechanism, 8 ... Control rod guide tube, 9 ... Core upper mechanism, 10
…… Center plug, 11 …… Poison rod plug, 12
...... Core support, 13 ...... Radial reflector, 14 ...... Control rod absorber, 15 ...... Fuel transfer pot, 16 ...... Fuel assembly duct, 17 ...... Fuel pin, 18 ...... Fuel assembly, 19 ... Coolant inflow hole, 20 ... Convex part, 21 ... Handling head, 22 ...
… Poison rod insertion tube, 26 …… inlet hole, 27 …… coolant inlet hole, 28 …… concave groove, 30 …… poison rod.

Claims (3)

[Claims] 1. In a liquid metal cooling fast reactor of the type in which an integrated fuel assembly is put in and taken out from a center plug in the upper part of a furnace, a fuel transfer pot which can be put in and taken out from the center plug and into which the fuel assembly is inserted and loaded. And a means for opening and closing a coolant inlet hole for forming a coolant inlet hole on the lower surface of each of the fuel assembly duct and the fuel transfer pot of the fuel assembly to connect and disconnect both coolant inlet holes. A small liquid metal-cooled fast reactor. 2. The small-sized liquid metal cooling fast reactor according to claim 1, wherein the means for opening and closing the coolant inflow hole is a concavo-convex engagement mechanism provided on the fuel assembly duct side and the fuel transfer pot side. 3. A small-sized liquid metal cooled fast reactor according to claim 1, wherein a poison rod insertion pipe is provided upright in the center of the fuel assembly duct, and the poison rod can be inserted into the poison rod insertion pipe from outside the reactor.