JPS6151748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactor internal structure of a light water nuclear reactor,
In particular, by enclosing the core in the radial direction with hollow lattice plates that support the fuel assemblies and ensuring the flow rate of coolant flowing through the fuel assemblies, channel boxes surrounding the fuel rods are not required, and the By providing holes, the emergency core cooling system (hereinafter referred to as
This relates to reactor internals that have the functions of ECCS) and boric acid water injection system (hereinafter referred to as SLC).

The conventional reactor internals and system configurations of ECCS and SLC are shown in Figures 1 and 2, respectively. A conventional reactor internal structure includes an upper grid plate 2 for supporting a fuel assembly 1, a lower grid plate 3 for supporting a fuel assembly 1, and control rods 4 and LPRMs 5 for controlling and monitoring nuclear reactions in the reactor core.

Further, in the fuel assembly 1, the fuel rods 6 are surrounded by a channel box 7 in order to ensure a flow rate of coolant flowing through the fuel assembly and to give strength to the fuel rods 6.

However, since Channel Box 7 was made of expensive Zircaloy and was disposable, it had the following three drawbacks.

(a) Problem of secondary waste Because the channel boxes were activated by neutron absorption, radioactive secondary waste was generated every time the fuel was replaced. Currently, fuel and channel boxes 7 are highly radioactive secondary wastes, but since fuel is reused after being reprocessed, the disposal of channel boxes 7 has become the biggest problem.

(b) Problem of high cost Since the channel box 7 is made of expensive Zircaloy, the cost of the fuel assembly 1 is high.

(c) Work process during gamma scanning During regular inspections, gamma scanning is performed to confirm the integrity of the fuel rod 6. During this process, the channel stator is removed and the channel box 7 is inserted into the fuel rod. 6 and is separated from the fuel rod 6 to perform gamma scanning of the fuel rod. This caused a lot of time and trouble for the workers.

In addition, the conventional SLC handles a hypothetical accident (hereinafter referred to as
The boric acid water stored in the boric acid water storage tank 12 is injected into the ATWS by the boric acid water injection pump 11 through the boric acid water injection nozzle 9 provided in the lower plenum by remote manual operation of the explosion valve 10. and shut down the furnace.

However, SLC had the following problems due to its system configuration.

(d) Problems related to rapid injection of boric acid water Since the boric acid water injection nozzle 9 is installed in the lower plenum, the boric acid water stagnates in the lower plenum and cannot be quickly injected into the core.

Furthermore, in the event of a loss of coolant accident (hereinafter referred to as LOCA), the conventional ECCS sprays cooling water through a core spray system 13 installed at the top of the core to cool the core.

However, ECCS had the following problems due to its system configuration.

(e) Problem with core spray distribution Even if cooling water is sprayed at the top of the core, the steam generated in the core obstructs the flow of cooling water into the core, so a uniform spray water distribution cannot be obtained. , a large amount of cooling water is required to cool the furnace.

The object of the present invention is to provide a channel box 7,
The purpose of this project is to provide an economical and highly reliable light water reactor by providing ECCS and SLC functions to the core support structure.

The present invention uses a reactor internal structure consisting of a hollow lattice plate with holes divided along the axial direction to prevent the lateral flow of coolant that occurs in the core during normal operation, and to reduce the flow of coolant per fuel assembly. It secures the coolant flow rate, eliminates the need for channel boxes, and has SLC functionality during ATWS and ECCS functionality during LOCA.

This has the effect of easing the economic burden when manufacturing channel boxes and suppressing the generation of secondary waste, as well as allowing spray water or boric acid water to be directly injected into the reactor core depending on the type of accident. There is.

An embodiment of the present invention will be described with reference to the drawings.

The present invention is a core support structure 17, as shown in FIG. 3, located within a nuclear reactor core. This core support structure 17 consists of a lattice plate 18 that divides the core in the radial direction, and this lattice plate 18 has holes in it.
It is a hollow structure with 9.

The control rods 4 are inserted into the center of the area surrounded by the grid plate 18, and are inserted between the control rod guide plates 20 fixed around the control rods 4 to avoid contact between the control rods 4 and the fuel rods 6. The reaction can be controlled by raising and lowering the temperature.

Further, the area defined by the control rod guide plate 20 and the grid plate 18 is designed to ensure a sufficient flow rate of coolant per fuel assembly.

Also, at the intersections of the grid plates 18, LPRM guide pipes 21 are installed.
LPRM5 is installed in it to monitor nuclear reactions in the reactor core.

In the present invention, every fourth fuel assembly 1 from which the channel box 7 has been removed is inserted into each area divided by the grid plate 18.

This makes it possible to secure the coolant flowing through the fuel assembly 1 and maintain a good core power distribution.

Furthermore, in the conventional example, in order to efficiently control nuclear fission in the reactor core and monitor it accurately, control rods 4 and LPRM
5 was placed outside the channel box 7 in an area free of steam bubbles.

Also in the present application, control by the control rods 4 is performed inside the control rod guide plate 20 that does not contain air bubbles, and the LPRM
Since the monitoring by 5 is carried out in the guide tube 21, the same effect as before can be achieved.

Furthermore, by providing a plurality of holes 19 in the hollow lattice plate 18, during LOCA, from these holes 19,
ECCS cooling water is injected to cool the core and ATWS
Sometimes, the structure is such that the furnace can be shut down by injecting SLC boric acid water.

Figure 4 shows this system configuration. This system configuration uses signals from the reactor at the time of an accident to indicate that an accident is LOCA.
Controller 2
3, in the case of LOCA, the ECCS valve 14 and pump 15 are operated to inject the cooling water in the tank 16. During ATWS, the SLC's explosion valve 10 and boric acid water injection pump 11 are operated to inject boric acid water in the boric acid water storage tank 12.

As shown above, the core support structure 17 has sufficient functions of the channel box 7, ECCS, and SLC.

By this, the following six effects can be obtained.

(a) Reduction of secondary waste With the abolition of Channel Box 7, secondary waste that is activated by neutron absorption will no longer be generated.

Moreover, for this reason, the side banging force required to store the channel box 7 for a long period of time becomes unnecessary.

(b) Cost reduction Instead of disposable channel boxes 7,
By installing the provided core support structure 17, the manufacturing cost of the fuel assembly can be significantly reduced, and the manufacturing process can also be shortened.

This makes it possible to provide an economical nuclear power generation facility.

(c) Shortening the work process during gamma scanning During periodic inspections, gamma scanning is performed to confirm the integrity of the fuel rods 6, but the process of separating the channel box 7 is no longer necessary, and the process can be shortened. It can be significantly shortened. Furthermore, the radiation exposure of workers during work can also be reduced.

(d) Direct spraying of ECCS cooling water ECCS cooling water can be directly sprayed onto the fuel rods 4 from the holes 19 on the grid plate 18, and cooling water injection into the reactor core is not obstructed by the steam generated in the reactor core. , can effectively cool the core. Additionally, ECCS water can be sprayed uniformly throughout the core.

(e) Improved SLC reliability Since the SLC boric acid water is directly injected into the reactor core through the holes 19 on the grid plate 18, the problem of boric acid water stagnation in the lower plenum as in the conventional case is solved, and neutron absorption The effectiveness of the agent is improved and the furnace can be shut down quickly.

(f) Improving earthquake resistance By forming the core support structure 17 into an integral structure, the earthquake resistance of the core can be improved.

In particular, as shown in FIG.
By installing the reinforcing material 22 in the structure, earthquake resistance can be further improved.

FIG. 5 shows another embodiment of the invention.

In this example, the ECCS line and
This is an example of setting different rules for SLC lines that have the same piping. Especially for SLC,
Since steam is generated in the upper part, the moderating effect of neutrons in the upper part is relatively small, and the output is higher in the lower part, so the neutrons are injected into the core support structure 17 from the lower part.

According to the invention, channel boxes, ECCS
By providing the core support structure with SLC functions, we were able to provide an economical and highly reliable nuclear reactor.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the inside of a conventional reactor core, Fig. 2 is an explanatory diagram of conventional ECCS and SLC, Fig. 3 is an explanatory diagram of the reactor internal structure of the embodiment of the present invention, and Fig. 4 is an explanatory diagram of the reactor internal structure of the embodiment of the present invention. Explanatory diagram of the system configuration of ECCS and SLC in the example, Part 5
The figure is a drawing showing another embodiment of the present invention. 1...Fuel assembly, 2...Upper grid plate, 3...
Lower grid plate, 4...Control rod, 5...LPRM, 6...
...Fuel rods, 7...Channel boxes.

Claims (1)

[Claims] 1. In the core of a light water reactor, the core is characterized by an integrated structure consisting of multiple hollow lattice plates with a large number of holes that divide the flow of coolant in the radial direction within the core, surround the fuel assembly over its entire length, and have a large number of holes. core support structure.