JPS59222790A - Auxiliary core cooling system of liquid metal cooled reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an auxiliary core cooling system for a nuclear reactor, and particularly to an auxiliary core cooling system suitable for use in a nuclear reactor that uses liquid metal as a coolant. .

[Background of the invention]

FIG. 1 shows an example of an auxiliary core cooling system in a conventional liquid metal cooled nuclear reactor. In FIG. 1, there is a cover gas space 21 of inert gas above the liquid metal in the reactor vessel. During normal reactor operation, the heavy pressure and cold liquid metal in the lower plenum 2 of the reactor vessel 1 cools down the heat generated in the reactor core 3, flows into the lower pressure and hot upper plenum 4, and flows out through the outlet nozzle 5. After being cooled by the intermediate heat exchanger 6 in the primary main cooling system, the pressure is increased by the primary main circulation pump 7, and the fluid flows through the inlet nozzle 8 and into the lower glenum 2 again. Usually, a plurality of such main cooling systems are installed independently. The heat transferred to the secondary main cooling system by the primary main cooling system intermediate heat exchanger 6 is further transferred to the steam system to rotate the turbine generator. During a reactor trip, the turbines are disassembled and the decay heat of the core is normally transferred to the indirect auxiliary core cooling system 9 (which uses part of the main cooling system).
(hereinafter abbreviated as IRAC8). IR
As a backup for AC8, there is a direct auxiliary core cooling system (hereinafter abbreviated as DRAC8) that cools the core without using the main cooling system. The DRA, C8 uses a magnetic bong 13 for the primary system, circulates the coolant in the upper plenum to the intermediate heat exchanger 12, cools it with the secondary coolant cooled by the air cooler 15, and then transfers it to the lower plenum. However, when not in operation, the outlet valve 14 is closed and the circulation of the primary coolant of the DRAC 8 is stopped. The characteristics of a liquid metal cooled nuclear reactor are that the difference in coolant temperature between the lower plenum 2 and the upper plenum 4 is very large, and the coolant has very good thermal conductivity. There is a problem in that during a trip, thermal shock is likely to be applied to the structural materials of the equipment. Especially in the upper plenum 4 inside the reactor vessel 1,
After the reactor trip, the cold liquid metal in the lower plenum 2 flows into the place where the liquid metal is hot during normal operation. The hot part 18 is the boundary surface 19
Temperature stratification occurs in which there is no flow in the hot portion 18.

This temperature stratification is caused by the occurrence of thermal stress due to a large temperature difference in the reactor vessel wall and reactor upper structure 20 near the temperature boundary surface 19, and by the mixing of cold liquid metal with hot liquid metal. The effect of mitigating thermal shock on piping and equipment after the exit nozzle 5 will be significantly reduced as the volume of the hot portion 18 no longer contributes to mixing, which will have a negative impact on the reactor structure. .

[Purpose of the invention]

An object of the present invention is to provide a liquid metal cooled nuclear reactor that uses DRAC5 and does not cause temperature stratification.

[Summary of the invention]

The invention is to reverse the flow of the DRAC 8 for a certain period of time after a reactor trip, and inject the cold liquid metal in the lower plenum 2 from the ring header 21 provided in the cover gas space 21 to the upper surface of the upper plenum 4. The material should not cause temperature stratification.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the present invention, and the configuration different from that in FIG. It is located where the piping 10 is connected. FIG. 4 shows the detailed structure of the upper part of the reactor vessel 1 in this embodiment. In FIG. 4, the upper core mechanism 2o and the fuel exchange device 24 are installed in the center of the upper part of the reactor vessel, so the ring header 22 is provided around the outer periphery of these reactor internals so as not to interfere with them. The ring header 22 is supported by providing a plurality of support beams 25 at equal intervals in the circumferential direction, one end of which is welded to the lower part of the ring header 22 and the other end of which is welded to the wall surface of the reactor vessel 1 which is in contact with the cover gas space. . The support beam 25 has a structure in which the welded portion with the reactor vessel 1 is located diagonally below the welded portion with the ring header 22, so that thermal displacement of the ring header 22 can be absorbed. Also, D
B. The passage of the outlet pipe 10 of the AC8 with the reactor vessel 1 is to be in the cover gas space 21 as far as possible from the liquid metal level in the reactor vessel, and the cold liquid metal in the lower plenum 2 is connected to the outlet pipe. When flowing, this prevents large thermal stress from occurring in the penetrating part due to the temperature difference with the hot liquid metal in the upper tube.

When a reactor trip signal is generated, the control rods scram to make the reactor core subcritical, so that the core thermal output becomes 2 to 3 inches below the rated output within 5 minutes after the scram.

The primary and secondary main circulation bongs receive the reactor trip signal and switch to low-speed operation to bring the core flow rate to approximately 10 g, and promptly start up all IRACs 8. During this operation, cold liquid metal begins to flow into the upper plenum of hot liquid metal from the core outlet at a low flow rate, so cold liquid metal gradually accumulates from the bottom. After a few minutes have elapsed, a temperature stratification interface will occur. In this embodiment, in order to prevent the occurrence of this temperature stratified interface, the D
By back-flowing the RAC 8, the cold liquid metal in the lower plenum 2 is transferred from the downcomer pipe 23 attached to the ring header 22 at a flow rate of about 1% or less of the core flow rate to the hot liquid metal stagnant on the upper surface of the upper plenum 4. The hot liquid metal is cooled by injection into the upper plenum, and the upper plenum is agitated.

The DRAC8 reverse flow operation is performed by converting the IRAC8 activation completion signal into an opening operation signal for the DR, AC8 outlet valve 14, which is an electric valve, through a delay circuit, and fully opening the outlet valve 14. At this time, the DRAGS electromagnetic port 1.3.16 and air cooler 15 are not activated.

Since the lower plenum 2 has a higher pressure than the upper plenum 4, this operation causes some of the liquid metal in the lower plenum to bypass the core 3, flow back through the DRAGS primary system, and return to the upper plenum. Injected.

In the event that more than one loop of multiple IRAC8s fails to start, or if an abnormality occurs in one or more of the IRAC8s during reverse flow operation of the DELAC8, the IR, &CS blower tachometer signal and the IRAC8 entrance/exit Detects an abnormality in III and AC8 using valve open/close signals, etc., generates an IR, AC8 abnormal signal, and immediately converts this signal into a DRAC8 outlet valve opening operation signal, and also displays a DRAC8 outlet valve fully open display proviso and an IRAC8 abnormal signal. The AND circuit of SI, DR,
By simultaneously starting the AC8 electromagnetic bongs 13 and 16 and the DRAC8 air cooler 15, DR can be quickly
, AC8 enters forward heat removal operation.

In this case, a temperature-stratified interface will occur within the reactor vessel, but it is sufficient to assume that the IRAC8 failure event within a few hours after a reactor trip occurs at most several times during the plant life. The structural integrity of the reactor is not compromised.

〔Effect of the invention〕

According to the present invention, a plurality of downcomer pipes 22 are provided on the ivy 21 to the ring.
are placed at equal intervals in the circumferential direction of the reactor vessel 1, and from this downcomer pipe 22, a small amount of the cold liquid metal from the lower blennium 2 is injected into the hot upper brenum 4 for a certain period of time after the reactor lip. This has the effect of uniformly dispersing the cold liquid metal into the hot liquid metal on the upper surface of the upper blenheim without interfering with the upper reactor mechanism zO in the center of the reactor vessel.

Furthermore, by injecting the cold liquid metal of the lower plenum 2 into the hot liquid metal of the upper surface of the upper plenum 4 after a reactor trip, temperature stratification in the upper plenum is prevented, so that the reactor vessel wall and primary main cooling This has the effect of eliminating thermal shock in system piping and equipment.

[Brief explanation of the drawing]

Figure 1 is a system diagram explaining the configuration of the conventional example, Figure 2 is a conceptual diagram explaining temperature stratification in the upper lunum of the reactor vessel after a reactor trip in the conventional example, and Figure 3 is a system diagram explaining the structure of the conventional example. FIG. 4 is a system diagram illustrating the configuration of the embodiment, and is a conceptual diagram of the structure of an embodiment of the present invention. 1...Reactor vessel, 2...Upper Blenheim, 3...
Core, 4...Lower blennium, 9...Indirect auxiliary furnace I cooling system, 6゜12...Intermediate heat exchanger, 7,13.16
...Bonfi,]9...Temperature boundary m1.22...
To the ring - 123...49 Phase Z side Figure 4

Claims (1)

[Claims] 1. In a nuclear reactor that has a plurality of auxiliary core cooling systems and uses liquid metal as a coolant, ring headers and downcomers are installed at some reactor vessel outlet nozzles of the auxiliary core cooling systems,
A liquid metal cooled nuclear reactor characterized by preventing the occurrence of coolant temperature stratification in the upper brenum of the reactor vessel by backflowing the auxiliary core cooling system in which the ring header is installed for a certain period of time after a reactor trip. auxiliary core cooling system.