JPH03215796A - Residual heat removal system of boiling water type nuclear 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 [Objective of the Invention] (Industrial Application Field) The present invention relates to a residual heat removal system having a low-pressure water injection mode for injecting emergency cooling water into a boiling water reactor. (Prior art) The low pressure water injection mode of the residual heat removal system of a boiling water reactor works together with other emergency core cooling systems in the event of a loss of coolant accident.
It is installed to prevent damage to the fuel cladding by restoring and maintaining the reactor water level. The low pressure water injection mode (LPCI) of the conventional residual heat removal system shown in Figure 2 will be explained below. Generally, a boiling water reactor 1 is equipped with two reactor recirculation lube systems 2a and 2b. A loss of coolant accident in a boiling water reactor occurs due to a pipe break in the recirculation loop 2a or 2b.

In addition, two systems of low pressure water injection mode (hereinafter referred to as LPCI) are installed in a general boiling water reactor (hereinafter referred to as LPCI-A3a and LPCI-B3b). One LPCI system has the capacity to inject water into reactor 1 via the unruptured reactor recirculation loop in the event of a loss of coolant accident, restore and maintain the reactor water level, and prevent fuel damage. ．． The LPC I-A3a has a suction pipe connected to an electric pump 6a1#6a, which has a capacity of 50% from the pool water 5 in the pressure suppression chamber 4, and further has an outer valve 8a and an inner valve 9.
recirculation loop A2 via injection line 7a with a
connected to a. Similarly, LPCI-B3b also pumps a 50% capacity electric pump 6 from the pool water S in the pressure suppression chamber 4.
A suction line is connected to b,, 6b, and via an injection line 7b with an outer valve 8b and an inner valve 9b to the recirculation loop Bib. LPCI-A
, B is provided with a tie line via a communication valve 10 on the outlet side of the pumps 6a1 to 6b2.

Since the LPCI is an emergency system, it does not need to operate under normal conditions, and the pumps 6a1 to 6b are stopped, and the outer valve 8a
, 8b and the communication valve 10 are open, and the inner valves 9a, 9
b is waiting in a closed state.

Hereinafter, a case where the recirculation loop 2b is broken will be explained as an example.

The LPCI-A3a sucks the pool water 5 in the pressure suppression chamber 4 into the pumps 6a and 6a, and the LPCI-B3b sucks the pool water 5 into the pumps 6b1 and 6b, respectively.

On the other hand, since the recirculation loop 2b is broken, the injection line 7a is selected as the injection line to be selected. Therefore, the outer valve 8a and the inner valve 9a are opened to bring the injection line 7a into the injection state, and the outer valve 8b and the inner valve 9b are closed to prevent injection into the injection line 7b. The reason why an open signal is sent to the open outer valve 8a and a close signal is sent to the closed inner valve 9b during standby is that these valves are automatically activated even if they are not in the standby state due to regular tests. This is to make the transition to

Therefore, the pumps 6b1, 6b of LPCI-B3b
The water discharged from 2 is transferred to the injection line 7a through the communication valve 1O, and is pumped into the pump 6a1 of LPC I-A3a.
16a, is injected into the reactor 1 via the unbroken recirculation loop A2a via the outer valve 8a and the inner valve 9a of the injection line 7a. Next, a conventional breaking loop selection method will be described with reference to the block diagram of FIG.

First, in step 20, the occurrence of a rupture in the recirculation loop is detected by a low reactor water level or high containment vessel pressure. Next, in step 21, by utilizing the fact that the pressure is lower in the recirculation loop where the rupture occurred, which recirculation loop has ruptured is determined by recirculation loops 2a and 2b.
Judgment is made based on the pressure relationship. The pressure relationship in this recirculation loop is detected by a differential pressure detector 11 provided between the recirculation loops 2a and 2b in FIG.

This is based on the pressure Pa of recirculation loop A and the pressure pb of recirculation loop B, taking into consideration the pressure difference δ that is sufficient to inject enough cooling water into the core even if there is an instrument error or incorrect selection.
This is done as follows. That is, if, for example, Pa≧Pb+δ is established based on one of the pressures, it is determined that the B loop is broken, and the A loop is selected in step 22. Conversely, P a < P b + δ
If so, it is determined that the A loop is broken, and the B loop is selected in step 23.

When the A-loop is selected, the injection line 7a of the A-lube is lined up 24 and the injection line 7b of the B-lube is blocked 25 as described above. vice versa,
If B loop is selected, injection line 7 of B loop
Lineup 26 of b and injection line 7a of A loop
Injection blocking 27 is performed.

(Problems to be Solved by the Invention) As described above, the LPCI is designed to deal with loss of coolant accidents, but the probability of a loss of coolant accident occurring is very low. On the other hand, recent studies such as probabilistic safety evaluation have shown that multiple failure accidents of multiple mitigation systems installed to alleviate and converge transient changes are more important than loss of coolant accidents. It has been pointed out that LPCI is required much more often in patients with LPCI. In this latter case, in fact, either recirculation lube 2a, 2b
Both have not broken. Furthermore, since no rupture has occurred, only a small amount of water needs to be supplied to reactor 1, so 50%
One capacity pump is sufficient.

This actually occurs much more frequently when both loops are not broken. Regarding the reliability of LPCI,
There were the following problems. In the conventional LPCI broken loop detection method, one of the broken loops is always selected. That is, if both loops are not broken, in the example described above, the pressure difference between both loops is less than δ, so Pa<Pb+δ, and loop B is selected in step 23 of FIG. Injection blocking 27 of the A-loop takes place. That is, even though the A loop is not broken, both the outer valve 8a and the inner valve 9a are closed.

Therefore, if the inner valve 9b of the injection line 7b of the selected loop B has a single failure and cannot be opened,
L. Although PCI has the redundancy of as many as four pumps, it has the disadvantage that the entire system loses its functionality.

Moreover, since such a situation accounts for most of the cases where LPCI is required, it has become a factor that greatly reduces the reliability of LPCI with respect to the safety of the entire nuclear reactor.

The present invention has been made in view of the above circumstances, and its purpose is to eliminate the need for injection lines in either of the two systems of LPCI when the recirculation loop has not broken, which is the majority of cases where LPCI is required. To provide a residual heat removal system that significantly improves the reliability of the entire LPCI without causing loss of functionality of the entire system due to a single failure of the LPCI by lining up for injection into the reactor. It is in.

[Structure of the invention]

(Means and effects for solving the problem) In order to achieve the above object, the present invention selects a healthy recirculation loop based on the pressure difference between the reactor recirculation loops and supplies emergency cooling water to the reactor. In the residual heat removal system of a boiling water reactor with low-pressure water injection mode, if none of the recirculation loops are broken, i.e. the pressure difference between the recirculation loops is caused by instrument error and misselection. Also, when the pressure difference δ is less than enough to inject sufficient cooling water into the reactor core, injection lines to both recirculation loops are lined up.

Therefore, according to the residual heat removal system of the present invention, the LPCI
injection line redundancy is provided in most cases where
It becomes possible to significantly improve the reliability of the entire LPCI.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. The same parts as in FIG. 3, which describes the LPCI loop selection method already explained, will be described with the same reference numerals. First, in step 20, the occurrence of a rupture in the recirculation loop is detected by a low reactor water level or high containment vessel pressure.

Next, in step 2l, by utilizing the fact that the pressure is lower in the recirculation loop where the rupture occurred, which recirculation loop has ruptured is determined by recirculation loops 2a and 2b.
Judgment is made based on the pressure relationship. This pressure relationship in the recirculation loop is detected by a differential pressure detector l1 provided between the recirculation loops 2a and 2b in FIG.

In step 21 above, when determining a rupture loop from the pressure relationship between the recirculation loops, consider the pressure difference δ that is sufficient to inject enough cooling water into the core even if instrument error and incorrect selection is made. When Pa≧Pb+δ,
As in the conventional case, it is determined that the B loop is broken, and the process proceeds to step 22.
Select A-lube at . Further, if Pb≧Pa+δ, it is determined that the A loop is broken, as in the conventional case, and the B loop is selected in step 23.

Furthermore, lPa where the pressure difference between both loops is less than or equal to δ
If Pbl<δ, it is determined that neither loop is broken, and in step 28, both the A loop and the B loop are selected. If either loop is selected in step 22 or 23, the selected loop is lined up and the unselected loops are blocked from being injected, as in the past, but it is determined that the loop is not broken. , step 28
When performing step 2, perform the A-loop lineup 24 and B-loop lineup 26, perform the lineup of injection lines for both loops, and perform step 2.
Steps 5 and 27 of blocking selection are not executed. [Effects of the Invention] As explained above, according to the present invention. LPG? LPCI injection line redundancy is provided in cases other than loss-of-coolant accidents, which is the majority of cases where LPCI injection lines are required.
This greatly improves overall reliability and makes it possible to take full advantage of the redundancy of the four pumps. In addition, since the part to be improved is part of the logic circuit that determines the pressure between the recirculation loops, there is no need for large-scale mechanical changes, so it can be introduced easily and inexpensively into existing plants. .

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining a broken loop detection method of LPCI according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of LPCI to which the present invention is applied, and FIG. 3 is a conventional LPC
FIG. 2 is a block diagram for explaining a broken loop detection method of I. 1... Nuclear reactor, 2a, 2b... Reactor recirculation loop, 3a, 3b-
L P C I system, 6a t 6a2 e 6b1e 6b2 '' Pump, 7a, 7b... Injection line, 8a, 8b... Outer valve, 9a, 9b... Inner valve, 10... Connection valve , l1...Differential pressure detector (8733) Representative patent attorney Yoshiaki Inomata (and one other person) Fig. E Fig. 2

Claims (1)

[Claims] In the residual heat removal system of a boiling water reactor, which has a low-pressure water injection mode that selects a healthy recirculation loop based on the pressure difference between the reactor recirculation loops and injects emergency cooling water into the reactor, A residual heat removal system for a boiling water nuclear reactor, characterized in that all recirculation loops are selected when there is no pressure difference between the recirculation loops.