JPS6230396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a safety device for a high-temperature gas-cooled nuclear reactor, and particularly to a safety device for a high-temperature gas-cooled nuclear reactor that can suppress floating of control rods when the pressure inside the reactor suddenly decreases.

Conventional high-temperature gas-cooled nuclear reactors (hereinafter referred to as high-temperature gas reactors) cool the core with helium gas pressurized to several tens of atmospheres in order to make the reactor outlet temperature of the coolant extremely high. The core of a nuclear reactor consists of a moderator made of graphite, a plurality of fuel rods, control rods arranged in parallel to the fuel rods, and a reflector. During normal operation, the coolant helium gas enters the lower plenum from the outer tube of the double-tube structure, rises along the reactor vessel, and enters the upper plenum.
Here, the fuel enters the fuel channel through the orifice of the flow regulating device, cools the fuel rods, and flows into the high-temperature plenum.The fuel enters the control rod channel through the orifice provided in the control rod guide tube and cools the control rods. Afterwards, they are separated into those that enter the high-temperature plenum at the bottom of the core. The helium gas that has entered the high-temperature plenum then enters the inner tube of the double-tube structure, passes through an intermediate heat exchanger, is pressurized by a circulator, and returns to the outer tube of the double-tube structure.

In the high-temperature gas reactor described above, the control rods are suspended by wire ropes from the control rod drive device installed at the top of the standpipe, and if the upper closure of the standpipe is damaged for some reason, the control rods The helium gas in the channel rapidly depressurizes from about 40 atmospheres to atmospheric pressure, and the helium gas flows back from the hot plenum to the control rod channel. At this time, the control rod may float due to the upward force caused by the reverse pressure differential generated at its upper and lower ends and the upward force caused by the viscous force of the helium gas flowing backward. This causes an increase in the reactivity of the nuclear reactor, which poses a problem to normal operation of the reactor.

The present invention has been made in consideration of the above-mentioned circumstances, and is a high-temperature gas-cooled nuclear reactor that can prevent the backflow of coolant that occurs in the control rod channel during rapid depressurization and prevent the control rods from floating. The purpose is to obtain safety equipment.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

As shown in Figure 1, the high-temperature gas furnace has a furnace vessel 1.
, the reactor core 2 housed inside it, and this reactor core 2
The control rod drive device 5 is comprised of a support member 3 that supports the reactor vessel 1, and a control rod drive device 5 that is located above the reactor vessel 1 and built into the stand pipe 4.

As shown in FIG.
A plurality of fuel rods 22 are inserted into fuel channels 21 that penetrate in large numbers in the axial direction of the moderator 20.
The upper reflector 23 installed on the upper part of the
It consists of a lower reflector 24 installed at the bottom of the 0, and a flow path switching section 30 placed under the lower reflector 24. The control rod 26 is inserted from a control rod drive device 5 installed above the reactor vessel 1 via a wire rope 27 into a control rod channel 28 arranged parallel to the fuel channel 21 . FIG. 3 and FIG. 4 are a vertical cross-sectional view and a cross-sectional view showing essential parts of the present invention. The flow path switching unit 30 is installed below the control rod 26, and includes an upper graphite block 32 that communicates with the control rod channel 28 and has a cooling flow path 31 with a spherical or conical lower portion.
, a lower graphite block 34 having a cylindrical recess and a coolant passage 33 communicating with the high temperature plenum 10 at its bottom; and a lower graphite block 34 located between the upper graphite block 32 and the lower graphite block 34. Block 3
The double cylinder 35 is fitted into the cylindrical recess of No. 4. A ball 37 made of a heat-resistant material is disposed between the inner cylindrical portion 36 of this double cylinder 35 and the upper graphite block 32. Double cylinder 35
The outer cylindrical part 38 and the inner cylindrical part 36 are joined together by four ribs 40, and the channels 41 and 42 connecting the coolant channels 31 and 33 are connected to the inner and outer parts of the cylindrical part 36. is formed. During operation, the ball 37 is depressed to the inner bottom of the inner cylindrical portion 36 and blocks the flow path 41. The diameter of this ball 37 is made larger than the length of the gap 45 formed between the lower surface of the upper graphite block 32 and the upper surface of the cylindrical portion 36, so that the ball 37 passes through the gap 45. It does not spill out from the inside of the cylindrical portion 36. Therefore, the ball 37 can only move between the inside of the cylindrical portion 36 and the spherical surface portion below the coolant flow path 31, and has a structure in which it will not deviate.

Next, the operation of the above device will be explained.

As shown in FIG. 1, helium gas, which is a coolant, enters the lower plenum 7 from the outer tube 6 of the double tube structure, then ascends through the gap 8 between the reactor vessel 1 and the reactor core 2, and flows into the upper plenum 9. After that, it descends to the core 2. Here, helium gas is in fuel channel 2.
1 and the control rod channel 28. The helium gas that has entered the control rod channel 28 flows through a flow path 31 , a flow path 42 , and a flow path 33 in this order, and then flows into the high temperature plenum 10 .

In a rapid depressurization situation, such as when the closure 29 at the top of the standpipe 4 (see Figure 2) is damaged, helium gas flows back from the high temperature plenum 10 to the control rod channel 28, but in a nuclear reactor equipped with the device of the present invention, The ball 37 is blown up by the helium gas suddenly blown out from the coolant flow path 41 and is pressed against the spherical surface of the flow path 31 .
to stop the flow of helium gas. At this time, since a pressure difference of several tens of atmospheres is generated between the high temperature plenum 10 and the control channel 28, the ball 37 remains stationary with the flow path 31 closed, and continues to prevent the backflow of helium gas.

As a result, the control rods are prevented from floating, and even in a state of rapid depressurization, the reactivity of the reactor is not applied, and safety can be maintained.

As explained above, according to the present invention, even if a backflow phenomenon occurs in the control rod channel when the coolant is in a state of rapid depressurization, the ball housed in the cylindrical portion is reliably operated and the control rod channel of helium gas is reliably operated. This prevents the control rod from floating back up.

Therefore, safe operation of the nuclear reactor can be ensured.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view schematically showing a high-temperature gas furnace;
FIG. 2 is an enlarged vertical cross-sectional view of the core of FIG. 1, FIG. 3 is a vertical cross-sectional view showing essential parts of an embodiment of the present invention, and FIG. 4 is taken along line AA in FIG. 3. FIG. 2... Core, 10... High temperature plenum, 28... Control rod channel, 31, 33... Coolant channel, 24... Lower reflector, 37... Ball, 30... Channel switching section, 41,
42...Flow path.

Claims (1)

[Scope of Claims] 1. A flow path switching member attached to the bottom surface of a lower reflector provided at the bottom of the core of a high-temperature gas-cooled nuclear reactor, and a control rod channel of the lower reflector passing through the flow path switching member. a coolant flow path that communicates between a cooling opening and a high-temperature plenum located in a lower portion of the reactor core; and a coolant flow path that communicates with the high-temperature plenum connecting portion of the flow path and the control rod channel connecting portion within the flow path switching member. a through section connecting the through section, a side passage section provided by piercing the through section, and a movable member that is supported at the upper end of the through section and blocking the flow of the through section, and the movable member A safety device for a high-temperature gas-cooled nuclear reactor, characterized in that the movable member is adsorbed to the control rod channel connecting portion of the flow path and closes the flow path when the pressure in the control rod channel suddenly decreases.