JPS6228692A - Method of operating nuclear-reactor coolant purification system - 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 provides a nuclear reactor that is effective in preventing the occurrence of thermal stress that may occur in water supply piping during reactor startup and shutdown of a boiling water type light water reactor. Cooling purification system (hereinafter abbreviated as "purification system"),
Concerning water supply systems and how to operate them.

[Background of the invention]

Conventionally, a line is installed to discharge excess primary cooling water to the condenser at the time of reactor startup.

The purpose of this installation is to release surplus water for adjusting the reactor water level, and as in the present invention, in order to prevent the phenomenon in which high-temperature water and low-temperature water separate into layers in the water supply pipe, it is necessary to release surplus water according to the water supply flow rate. , there is no known method for discharging purified water into a condenser.

FIG. 3 shows the configuration and reactor startup according to the prior art. The purification system has already started operating during the reactor cold shutdown, and is operated in the following order: reactor 1 → purification system pump 5 → regenerative heat exchanger 7 → non-regenerative heat exchanger 8 → filtration desalination device 10 → regenerative heat exchanger 7 → Water supply piping 22
→Reactor coolant is circulated through the reactor 1 route.

Thereafter, in the reactor temperature and pressure increasing process after the control rods are withdrawn, the temperature and pressure at the inlet and outlet of the purification system gradually rises as the temperature and pressure of the reactor 1 increases. The coolant that has flowed into the purification system is transferred to the regenerative heat exchanger (tube side)7. After being cooled by the non-regenerative heat exchanger 8 and purified by the filtration and demineralization device 10, it is heated again by the regenerative heat exchanger (11M side) 7.

It becomes high temperature water and joins the water supply pipe.

On the other hand, in the operating state of the water supply system, before the turbine is started, when the reactor is in the process of increasing temperature and pressure and the amount of steam generated is small, the flow rate of the feed water is as small as the amount of steam generated, and the temperature of the feed water is about 30°C.

In addition, control rod drive water system inflow water 4 that flows into the reactor during the temperature and pressure rise of the reactor, as well as surplus water generated due to the expansion of the coolant, is purified as necessary to keep the reactor water level constant. It is discharged to the condenser 18 via the system blowdown valve 17.

The conventional method of operating the purification system and water supply system during reactor startup is as described above, but this method has the possibility of the following phenomena occurring.

That is, for a certain period before starting the turbine, purification system return water at about 200° C. and feed water at about 30° C. flow together in the water supply piping 22, but at this time, the water supply flow rate is small;
Because the two were not completely mixed at the confluence, there was a possibility that high-temperature purification system return water would flow into the upper part of the water supply pipe and low-temperature supply water would flow into the lower part. If this phenomenon were to occur, there would be a temperature difference between the upper and lower parts of the piping, causing thermal stress in the piping.

JP-A-57-149996 discloses a structure in which purification system piping is connected to water supply piping via a recombination tee. However, this known example does not provide a method for preventing the occurrence of thermal stress in the water supply piping due to the purification system water becoming high temperature and the supply water becoming low temperature during the startup and shutdown of the nuclear reactor.

[Purpose of the invention]

The purpose of the present invention is to prevent the occurrence of a phenomenon in which high-temperature water and low-temperature water separate into layers in an unmixed state, which could occur in water supply piping at certain times during the startup and shutdown of a nuclear reactor. The second objective is to prevent high-temperature purification system return water from flowing into the water supply piping during periods when this phenomenon is likely to occur.

[Summary of the invention]

As a result of a survey of plant operation data, we found that reactor startup and
Under certain water supply conditions and purification system conditions during shutdown, a phenomenon occurs in which high-temperature purification system water and low-temperature supply water separate into layers in an unmixed state in the water supply piping (hereinafter referred to as "stratified flow phenomenon" in the text). It has been found that this may occur.

The stratified flow phenomenon may occur when the temperature of the purification system return water flowing into the water supply piping is high, the supply water is low temperature (approximately 30° C.), and the flow rate is small. When the water supply flow rate is small, the water supply and the purification system water that joins it do not mix sufficiently, so low-temperature water portions and high-temperature water portions coexist within the pipe. When low-temperature water and high-temperature water coexist, buoyancy acts on the high-temperature water due to the density difference between the two, causing the high-temperature water to rise to the top of the pipe and the low-temperature water to sink to the bottom of the pipe, resulting in a laminar flow of high-temperature and low-temperature water. arise.

Such a phenomenon does not occur when the flow rate of the water supply increases and the flow within the water supply piping is sufficiently disturbed and the water supply and purification system water are sufficiently mixed.

Therefore, in the conventional nuclear reactor start-up/shutdown method, there is a possibility that conditions for the occurrence of the inner stratification flow phenomenon in the water supply pipes may be established during a certain period when the reactor is in a high temperature state and the turbine is not operating.

In the present invention, when the water supply flow rate is low and within the range of stratified flow generation conditions, stratified flow is prevented by not allowing purified water to join the water supply piping and discharging it to another location, that is, the condenser. I devised something.

Conventionally, the purification system has been provided with blowdown piping for discharging surplus water caused by expansion of reactor water to a condenser as needed during reactor startup. Therefore, during the period when the purified water is not returned to the water supply pipe, the purified water can be continuously discharged to the condenser through the blowdown pipe.

This operating method is fully possible in terms of water balance and heat balance as shown below. In terms of water balance, by discharging the entire amount of purified tea water to the condenser, reactor water that exceeds the amount of surplus water will flow out of the reactor, so it is necessary to consider replenishing the excess flow through water supply. To deal with this, conventionally the flow rate of water supply is controlled to keep the reactor water level constant when the reactor is started before the turbine is started, and even when the entire amount of purified permeable water is released into the condenser, the reactor water level will still drop. There's nothing to do.

In addition, thermally, the amount of heat held by the purification system water is released to the condenser, and this amount of heat loss occurs when the reactor is started, but the period of operation in this operation mode is limited to a certain period at the time of start-up. There is no problem because the flow rate of the purification system is only about 2% of the rated water supply flow rate.

As mentioned above, when the water supply flow rate is within the range of stratified flow generation conditions, operation in which the purified water is not returned to the water supply pipe and the entire amount is blown down to the condenser is effective in preventing stratified flow generation, and
It was shown that it is possible.

[Embodiments of the invention]

(Example 1) An embodiment of the present invention is shown in FIG.

In this embodiment, the blowdown valve 1 is
7 is fully open, and the purification system outlet valve 15 is fully closed. This operation is performed when the purified system water is not returned to the water supply pipe 22 and the entire amount is discharged to the condenser 18 in order to prevent the stratified flow phenomenon from occurring.

Furthermore, in this embodiment, the flow meter 21 detects the water supply flow rate,
To prevent the occurrence of stratified flow, an interlock is provided to automatically close the purification system outlet valve 15 and open the blowdown valve 17 when the water supply flow rate is within a range that requires full blowdown to the condenser.

The reactor startup method according to this embodiment will be described below. First, the purification system is activated during cold shutdown of the reactor. However, at this time, the purification system shall be operated at 50% capacity, and only one of the two 50% capacity purification system pumps 5 will be started, and the 50% capacity of the two pumps will be activated.
The operation switches 6 and 14 are operated so that only one of the capacity filtration demineralizers 10 is allowed to pass water. This occurs when the purification system outlet valve 15 is fully opened and the blowdown valve 17 is fully opened.
1. Because the cooling effect of the regenerative heat exchanger 7 cannot be expected.
The flow rate of the purification system is reduced to such an extent that it can be cooled down to the inlet temperature condition (approximately 50° C. or lower) of the filtration salt theory device 10 only by the cooling capacity of the non-regenerative heat exchanger 8. Flow meter 21
When the water supply flow rate detected by is O, the purification system outlet valve 15
There is an interlock between closing the blowdown valve 17 and opening the blowdown valve 17. The flow rate of the purification system is automatically adjusted to the rated flow rate for each salt filtration device by the flow control valve 12 at the outlet of the salt filtration device 11.

In order to replenish the supply water corresponding to the rated flow rate of the purification system flowing out from the reactor through the purification system to the condenser, the opening degree of the water supply flow rate control valve 2o is adjusted by the water supply control bag @26. The water supply control device receives the reactor water level signal and performs control to keep the reactor water level constant.

After that, the control rods are pulled out from the reactor and the temperature and pressure of the reactor is increased. However, while the feed water flow rate is within the range where stratified flow may occur, the purification system outlet valve 15 is closed and the blowdown valve 1 is closed.
7 will remain open. After the amount of steam generated increases as the temperature and pressure of the reactor increases and the turbine bypass valve 25 is opened,
The flow rate of feed water also increases as the amount of steam generated increases. after that,
By the time the amount of steam generation increases and the main steam turbine stop valve 24 is opened to start the turbine, the amount of water supplied will further increase. Stratified flow downstream of the junction of the water supply pipe and the purification system is no longer likely to occur when the water supply flow rate increases. The flow meter 21 detects the water supply flow rate, and when a sufficient flow rate is reached, an interlock is established in which the purification system outlet valve 15 is fully opened and the blowdown valve 17 is fully closed. After this, purification system pump 5
Operates two cars.

Two salt filtration devices will be operated. The subsequent steps are the same as the conventional method, and during normal operation of the water supply control device 26,
Water supply control is performed by receiving signals for reactor water level, main steam flow rate, and water supply flow rate.

When the nuclear reactor is shut down, the purification system outlet valve 15 is fully open and the blowdown valve 17 is fully open when the feed water flow rate is low, and vice versa in other feed water flow rate ranges, similar to when the reactor is started. The purification system is operated at 50% capacity during full blowdown operation, and this also applies when the system is stopped.

In this example, by setting the flow rate of the purification system to 50% when performing full blowdown operation, the heat loss generated due to discharge to the condenser is also reduced when performing full blowdown at 100% flow rate of the purification system. As half of that, heat loss is kept to a small level.

(Example 2) An embodiment of the present invention is shown in FIG.

The main feature of this embodiment is that the blowdown valve bypass valve 28 is fully open and the purification system outlet valve 15 is fully closed at a certain time during startup and shutdown. This operation is performed when the purified system water is not returned to the water supply pipe 22 and the entire amount is discharged to the condenser 18 in order to prevent the stratified flow phenomenon from occurring. Furthermore, in this embodiment, the flow rate of the water supply is detected by the flow meter 21, and when the flow rate of the water supply is in a range that requires blowing down the entire amount to the condenser in order to prevent the occurrence of stratified flow, the purification system outlet valve 15 is automatically activated. is closed and the blowdown valve bypass valve 28 is opened.

The reactor startup method according to this embodiment will be described below. First, the purification system is activated during cold shutdown of the reactor. At this time, the water supply flow rate is O, so the purification system operates at the rated flow rate with the purification system outlet valve 15 closed and the blowdown valve bypass valve 28 open.

Next, the control rods are pulled out of the reactor and the temperature and pressure of the reactor begins to increase. In the process of increasing the temperature and pressure, the feed water control bag @26 receives the reactor water level signal, adjusts the opening of the blowdown valve 17 and the feed water flow rate control valve 20, and performs coordinated control of the blowdown flow rate and the feed water flow rate. Keep reactor water level constant. On the other hand, the feed water flow rate increases as the amount of steam generation increases.

As the reactor heats up and the amount of steam generated increases, the turbine bypass valve 25 opens and the main steam turbine stop valve 24 opens, so the feed water flow rate increases.

The flow meter 21 detects that the water supply flow rate has increased sufficiently,
With this flow rate signal, the purification system outlet valve 15 is opened and the blowdown valve bypass valve 28 is switched to normal operation.

The subsequent steps are the same as the method according to the prior art.

When the reactor is shut down, as in the case of startup, if the water supply flow rate is low, the purification system outlet valve 15 is fully closed and the blowdown valve bypass valve 2 is closed.
8 Fully open, the water supply flow rate is large, and the valve is in the reverse open/close state.

In addition, in Example 1, the purification system was operated at 50% capacity at the time of startup, whereas in this example, the purification system was operated at 1 capacity from the time of startup.
00% operation, which is more advantageous than Example 1 in terms of purification ability.

〔Effect of the invention〕

According to the present invention, it is possible to eliminate the possibility of occurrence of the phenomenon of stratified flow inside the water supply pipes during startup and shutdown of the nuclear reactor.

When stratified flow occurs, high-temperature water flows in the upper part of the water supply pipe and low-temperature water flows in the lower part, creating a temperature difference between the upper and lower parts of the pipe, and this temperature difference causes the upper part of the pipe to expand more than the lower part. shall be.

That is, thermal stress is generated that tends to bend the piping.

Therefore, if a plant is to be operated while allowing stratified flow, a water supply piping support structure is required that has sufficient strength to support the thermal stress generated by stratified flow. Another disadvantage is that the water supply pipe itself becomes fatigued.

According to the present invention, since the occurrence of stratified flow can be prevented, there is no need to take this phenomenon into consideration, and there is an advantage that both the quantity and quality of water supply piping support structures can be rationalized compared to the case where the occurrence of stratified flow is taken into consideration. . In addition, fatigue of water supply piping can be reduced.
Plant safety.

Improved reliability.

[Brief explanation of the drawing]

FIGS. 1 and 2 are embodiments 1 and 2 of the present invention.
Fig. 3 shows a state diagram of the purification system water/metal flow blowdown operation when starting and stopping the nuclear reactor, and Fig. 3 shows a configuration according to the prior art and a state diagram when starting and stopping the reactor. DESCRIPTION OF SYMBOLS 1... Nuclear reactor, 2... Recirculation pump, 3... Recirculation piping, 4... Control rod drive water system, 5... Purification system pump, 6... Operation switch, 7...・Regenerative heat exchanger, 8
...Non-regenerative heat exchanger, 9...Auxiliary cooling water system, 10...
・filtration desalination device, 11...flow meter, 12...flow control valve, 13...filtration desalination device outlet valve, 14...operation switch, 15...purification system outlet valve, 16. ...Operation switch, 17...Blowdown valve, 18...Condenser, 19...Water supply pump, 2゜...Water supply flow rate control valve,
21... Flow meter, 22... Water supply piping, 23... Main steam piping, 24... Main steam turbine stop valve, 25...
Turbine bypass valve, 26... Water supply control device, 27.
...Turbine, 28 river blowdown valve bypass valve.

Claims (1)

[Claims] 1. The coolant taken out from the nuclear reactor is transferred to a pump, a heat exchanger,
In the reactor coolant purification system, which is purified by the filtration desalination equipment and returned to the water supply piping, a stop valve is installed at the outlet of the connecting pipe to the water supply piping, and purified water after passing through the filtration desalination equipment is transferred to the turbine condenser. When the water supply flow rate is small depending on changes in the water supply flow rate, the stop valve at the outlet of the connection pipe to the water supply pipe of the purification system is closed, and the return flow rate to the water supply pipe is reduced to zero. All purified water is discharged to the turbine condenser, and when the water supply flow rate exceeds a specified amount, the stop valve at the outlet of the connection pipe to the water supply pipe of the purification system is opened and the purified water is returned to the water supply pipe. Characteristic method of operating the reactor coolant purification system. 2. Claim 1 states that a flow meter is provided in the water supply piping to detect the water supply flow rate, issue a water supply flow rate signal, and thereby provide an interlock that automatically opens and closes the valve. Characteristic method of operating the reactor coolant purification system.