JPS6055798B2 - Drain removal device in the reactor containment vessel sandwich section - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drain removal device for a sand cushion portion of a nuclear reactor containment vessel in a nuclear power plant.

Generally, the sand in the sand cushion has the function of relieving local stress on the wall of the containment vessel in the event of an accident, and in order to fully utilize this function, it is necessary to maintain a dry state. Conventionally, as shown in FIGS. 1 and 2, a drain removal device for a sand cushion part of a Mark-■ type reactor containment vessel, for example, has been used to
Valves 5a, 5b penetrate through the biological shielding wall 2 surrounding the reactor containment vessel 1 and extend from the sand cushion part 3 provided between the reactor containment vessel 1 and the biological shielding wall 2 to the reactor building indoor floor drain funnels 4a, 4b, 4c. It is known that pipes 5 having the following characteristics are provided at several locations on the circumferential surface of the sand cushion portion 3.

However, with this type of drain removal device, water cannot be drained from the piping inlet 6 to the bottom of the sand cushion, and the piping is routed on the floor of the reactor building, which obstructs the passageway, and the sand cushion The sand inside gradually flows out, making it difficult to maintain the function of the sand cushion.

Further, since the valves 5a and 5b are exposed inside the reactor building, there is a drawback that the structure inside the reactor building becomes complicated. The present invention solves the above-mentioned conventional drawbacks, and when water flows into the sand cushion part 3 for some reason, it is possible to more reliably drain the water to the outside without mixing the sand in the sand cushion part 3. An object of the present invention is to provide a highly reliable drain removal device for a sand cushion portion of a nuclear reactor containment vessel.

The present invention will be explained below based on an embodiment shown in FIGS. 3 to 6.

As shown in FIGS. 3 and 4, a biological shielding wall 2 is provided around the outer periphery of the reactor containment vessel 1 at a required distance from the reactor containment vessel 1.

The bottom of the gap between the biological shielding wall 2 and the reactor containment vessel 1 is filled with dry sand, forming a sand cushion portion 3 in this portion. At the lower end of the sand cushion section 3, as shown in an enlarged view in FIG. 5, a downwardly sloped sand prevention mechanism 100 is provided embedded in the concrete of the biological shielding wall 2. As shown in an enlarged view in FIG. 6, this sand prevention mechanism 100 includes a gravel filling cylinder 7, a sand prevention screen 8, a perforated flange member 9, and a drain collection box 10 connected in this order. A riser pipe 11 is protruded from the lower surface of the drain collection box 10, and the riser pipe 11 is located below the sand cushion portion 3 as shown in FIG. The ring header 12 is connected to a ring header 12 which is arranged at an angle.

The ring header 12 is located outside the reactor containment vessel 1, as shown in the horizontal sectional view of FIG. 4, and is embedded in concrete 16. In this example, ring header 1
2 literally uses a ring with unnecessary parts cut out instead of a ring. One pipe 13 is connected to the inclined lower end position 12a of the ring header 12 (
(See Figure 3).

This piping 13 is connected to a backflow preventer 14 such as a check valve.
It communicates with a sump tank 15 located in one block 17 on the floor of the reactor building (see FIG. 4). As shown in detail in FIG. 6, the gravel filling cylinder 7 is filled with gravel 7b packed in a wire mesh 7a so that the grain size gradually increases toward the double anti-sand screen 8. ing.

(In this example, it is divided into three types of particle size.) Also,
The sand prevention screen 8 is made of glass cloth, synthetic resin cloth, or other suitable material, and has a cross section of approximately I
Together with the drain collection hole 9a provided in the pressure-resistant perforated flange member 9 and the gravel 7b, sand is prevented from flowing into the drain collection box 10. In addition, sand control mechanism 1
It is preferable that a plurality of numbers 00 are provided in the circumferential direction of the sand cushion portion 3.

In addition, the underground floor of the reactor building is divided into, for example, three blocks by separation walls 2a, 2b, and 2c to prevent water from flooding inside the building, so that even if an accident such as a pipe breakage occurs, water will not flow into other blocks. It is configured so that it does not. Next, the operation of the above device will be explained.

Water may enter the sand cushion portion of the reactor containment vessel due to the following reasons.

(b) Water condensed on the outer wall surfaces of the biological shielding wall 2 and the reactor containment vessel 1 due to air between the biological shielding wall 2 and the reactor containment vessel 1 due to changes in operation or air conditioning conditions in the building.

(Note) Water that has condensed on the walls of the reactor containment vessel or water that has leaked from an isolation valve and has flowed in through piping.

(c) Groundwater that seeps into the sand cushion from outside the foundation mat through concrete pour joints, etc.

These waters first accumulate at the lower end of the sand cushion section 3 and flow into the sand prevention mechanism 100.

At this time, the gravel 7b prevents sand from flowing out to some extent, and the sand prevention screen 8 completely prevents sand from flowing out.

The water that has flowed into the drain collection box 10 flows through the riser pipe 11 and is led to the cylinder header 12, and then to the pipe 13.
and flows into the sump tank 15 via the check valve 14.

The present invention has been described above based on the preferred embodiments. According to the present invention, by using a ring header, the requirements for system separation in the underground floor of a reactor building can be satisfied with high reliability. Also, the number of drain locations can be easily increased as needed.

Furthermore, water can be drained from the sand cushion portion reliably, and the large number of valves 5a and 5b required in the prior art is not required, which is also effective from an economic point of view. Furthermore, even if the number of drain points increases, only one ring header is required, so there is no need to open or close valves, and the complexity of work can be eliminated. In other words, a check valve, which is a backflow preventer, is installed in the middle of the piping, and when water collects in the drain collection box, this valve opens at the head of the water and automatically guides the water through the piping to the sump tank. With this configuration, there is no need for an operator to open or close the valve.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of a conventional drain removal device for a sand cushion section of a reactor containment vessel, FIG. 2 is a horizontal sectional view taken along line A-A in FIG. 1, and FIGS. 3 is a schematic vertical sectional view, FIG. 4 is a horizontal sectional view taken along line B-B in FIG. 3, FIG. 5 is an enlarged sectional view of the lower end of the sand cushion part, and FIG. is an enlarged cross-sectional view of the opening for gravel filling. 1...Reactor containment vessel, 2...Biological shielding wall, 3...Sand cushion part, 7...
・Gravel filling cylinder, 7b... Gravel, 8...
- Sand control screen, 9... Perforated flange member, 10... Drain collection box, 1.2...
・Ring header, 13... Drain pipe, 14...
... Backflow preventer, 100 ... Sand prevention mechanism.

Claims (1)

[Scope of Claims] 1. A reactor containment vessel, a biological shielding wall provided around the outer periphery of the reactor containment vessel at a distance, and a biological shielding wall provided at the bottom of the gap between the biological shielding wall and the reactor containment vessel. A sand cushion portion filled with sand, a plurality of sand prevention mechanisms having an opening at the lower peripheral surface of the sand cushion portion and embedded in the bottom of the biological shielding wall, and hydraulically connected to each of the sand prevention mechanisms. Features include a ring header embedded near the bottom of the biological shielding wall, a drain pipe leading from the ring header to a single block in the reactor building, and a backflow preventer installed in the drain pipe. Drain removal device for the sand cushion section of the reactor containment vessel. 2. The sand control mechanism consists of gravel filled in a cylinder so that the particle size increases toward the downstream side, a sand control screen installed downstream of the gravel, and a sand control screen installed downstream of the sand control screen. A nuclear reactor containment according to claim 1, characterized in that the reactor containment comprises a perforated flange member which is a pressure-resistant structure, and a drain collection box provided on the downstream side of the perforated flange member. Drain removal device for container sand cushion section.