JPH06105314B2 - Reactor coolant purification system - Google Patents

Description

Description: FIELD OF APPLICATION OF THE INVENTION The present invention relates to a reactor coolant purification system effective for preventing the generation of excessive thermal stress that may occur in the feedwater piping at the time of reactor startup of a light water reactor. Regarding

[Background of the Invention]

FIG. 6 shows a system diagram of a reactor coolant purification system according to the prior art. The purification system has already started operation during the reactor cold shutdown, and the reactor 1 → purification system pump 4 → regenerated heat exchanger 5 → non-regenerated heat exchanger 6 → filtration desalination device 7 → regenerated heat exchanger 5 → Water supply piping
Circulate the reactor coolant through the route of 10 → Reactor 1.

After that, in the reactor temperature raising / pressurizing process after pulling out the control rods, the inlet / outlet temperature of the purification system gradually rises as the reactor 1 temperature raising / pressurizing. The coolant that has flowed into the purification system is cooled to a predetermined temperature by the non-regeneration heat exchanger 6 on the tube side of the regenerative heat exchanger 5, passes through the purification process by the filter desalting device 7, and then the body of the regenerative heat exchanger 5 again. Side is heated and becomes high temperature water
To join.

On the other hand, the operating condition of the water supply system is that the reactor 1 is in the temperature rising / pressurizing process and the amount of steam supplied to the turbine 11 through the main steam pipe 9 is small before the turbine is started. The flow rate of the water supplied from 13 is as small as the amount of steam generated, and the temperature of the water supply is approximately 30 ° C.

In addition, excess water in the purification system generated by expansion of the coolant during temperature rise and pressure rise in the reactor is maintained through the purification system blowdown valve 28 as necessary to keep the reactor water level constant. To release. 15 is a feed water flow control valve, which is a main steam flow meter
The water supply flow rate is controlled based on the signals from the 16, water supply flow meter 17, and the water supply flow rate control unit 18. 8 is a non-regenerative heat exchanger 6
Cooling system, 12 is a generator.

By the way, in such a purification system, the filter desalting device 7
The coolant (hereinafter referred to as purified water) that has passed through is passed through the regenerative heat exchanger 5 regardless of the feed water flow rate, heated to about 200 ° C., and returned to the feed water pipe 10. Therefore, for a certain period before the turbine is started, about 200 ° C of purification system return water and about 3
The 0 ° C feed water will join together and flow, but at this time, since the feed water flow rate is small and the mixing of both at the joining part is incomplete, high temperature purification system return water is present in the upper part of the water supply pipe. There was a possibility that a low-temperature water supply flowed to the lower part (hereinafter referred to as stratified flow phenomenon).

Should this stratified flow phenomenon occur, there will be a temperature difference between the upper part and the lower part of the pipe, resulting in excessive thermal stress in the pipe.

The stratified flow phenomenon is because the temperature of the purification system return water flowing into the water supply pipe is high (about 200 ° C) and the supply water is low (about 30 ° C).
May occur at low flow rates. In other words, when the feed water flow rate is small, the feed water and the purified water that joins the feed water do not mix sufficiently, so if the low-temperature water part and the high-temperature water part are mixed in the pipe, and if the low-temperature water and the high-temperature water are mixed, the density difference between the two As a result, buoyancy acts on the hot water, and the hot water rises in the upper part of the pipe,
Since the low temperature water sinks in the lower part of the pipe, a laminar flow of high temperature water and low temperature water is generated. Such a stratified flow phenomenon disappears when the feed water flow rate increases, the flow in the feed water pipe is sufficiently disturbed, and the feed water and the purified water are sufficiently mixed.

That is, as shown in FIG. 7, in the region where the feed water flow rate is extremely low [see FIG. 7 (b)], the temperature in the feed water pipe is almost uniform in the high temperature state due to the purification system return water (high temperature). However, as shown in FIG. 7 (a), high temperature water flows in the upper part of the pipe and low temperature water flows in the lower part of the pipe, and a stratified flow phenomenon occurs. Therefore, when the flow rate of the water supply is further increased, the flow velocity in the water supply pipe increases, and when the flow rate exceeds the predetermined water supply flow rate, the high temperature water and the low temperature water are mixed and the stratified flow phenomenon disappears.

Therefore, in order to prevent the stratified flow phenomenon, if a bypass is provided in the regenerative heat exchanger and the purification system water is guided to the bypass at a predetermined feed water flow rate or less, the temperature difference between the reactor feed water temperature and the purification system return water is reduced. By eliminating it, it becomes possible to avoid the stratified flow phenomenon.

By the way, as a purification device in which a regenerative heat exchanger is provided with a bypass, there are JP-A-56-66799 and JP-A-56-164997.

In order to remove the residual heat of the reactor, the purification devices described in both publications do not re-pass the purified water to the regenerative heat exchanger, but let it flow through the bypass into the feed water pipe to cool the hot feed water. It was made to let.

[Object of the Invention]

An object of the present invention is to provide a reactor coolant purification system that can prevent stratified flow phenomenon by allowing low-temperature purified water to flow from a purification device into a water supply pipe at the time of starting the reactor.

[Outline of Invention]

The gist of the present invention is to provide a regenerative heat exchanger and a non-regenerative heat exchanger for cooling a reactor coolant, and a desalination device for purifying the coolant that has passed through the non-regenerative heat exchanger. After passing the coolant purified by a salt device through the regenerative heat exchanger, in a reactor coolant purification system to be joined into the feedwater piping system of the reactor and returned to the reactor pressure vessel, The regeneration heat exchanger is provided with a bypass piping system, and is connected to a control circuit for inputting, as detection information, a temperature difference between the upper and lower sides of the inside of the piping on the downstream side of the confluence point of the water supply piping system and the feed water flow rate of the water supply piping system. And switching means for switching the flow of the coolant to the bypass piping system based on the output signal of the control circuit, and the control circuit stratifies at the confluence of the purification system and the water supply piping system at the time of reactor startup. Corresponds to the appearance range of flow It is configured to operate the switching means by comparing the set value to be detected with the detection information. By bypassing the regenerative heat exchanger, the reheating process of the coolant is omitted, and the low temperature in the cooling state is eliminated. The purified return coolant of (3) is made to flow into the water supply piping system.

Example of Invention

Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

FIG. 1 is a system diagram showing an embodiment of a reactor coolant purification system of the present invention, which is for a low pressure reactor. However, the same parts or those having the same functions as those of the structure shown in FIG. 1 is different from FIG. 6 in that a bypass pipe 30 equipped with a bypass valve 20 is provided on the reheated side of the regenerative heat exchanger 5, and the purified water purified by the filter desalination device 7 is It is made to flow into the water supply pipe 10 through the bypass pipe 30, and a regenerative heat exchanger inlet valve 21 is provided on the purified water inlet side of the reheated side of the regenerative heat exchanger 5, and the water supply flow meter 17 of the water supply pipe 10 is provided.
A flow rate switch 19 for controlling the opening and closing of the bypass valve 20 and the regenerative heat exchanger inlet valve 21 in response to a signal from is provided. This flow rate switch 19 outputs a signal that closes the regenerative heat exchanger inlet valve 21 when the feed water flow rate is low, and opens the regenerative heat exchanger bypass valve 20, and when the feed water flow rate increases. On the contrary, the regenerative heat exchanger inlet valve 21 is opened and a signal for closing the regenerative heat exchanger bypass valve 20 is output.

That is, when the feed water flow rate is small, the temperature of the purified water flowing into the feed water pipe 10 is such that the purified water passing through the filter desalting device 7 passes through the bypass pipe 30 without passing through the reheated side of the regenerative heat exchanger. The operating temperature of the filter desalting device 7 is low, for example, about 50 ° C.

Therefore, as shown in Fig. 5, the temperature of the supply water (about 30 ° C) and the temperature of the return water of the purification system (about
(50 ° C.), there is no big difference, so that the stratified flow phenomenon caused by the purified water flowing into the water supply pipe 10 being mixed with the water supply can be prevented. Then, when the flow rate of the supplied water increases, the purified water that has passed through the filter desalination device 7 is guided to the reheated side of the regenerative heat exchanger 5, is heated and flows into the water supply pipe 10, and the normal purification process is performed. Be done.

By the way, when bypassing the regenerative heat exchanger, the heat load for cooling the high-temperature (about 270 ° C) reactor water taken from the reactor 1 to the operating temperature (about 50 ° C) of the filter desalination device 7 is regenerated. The heat exchanger 6 is loaded. In order to increase the cooling capacity of the non-regenerative heat exchanger 6 in this case, it can be dealt with by increasing the flow rate of the cooling water system 8 of the non-regenerative heat exchanger 6. At that time, if the flow rate of the cooling water system 8 cannot be increased due to the piping configuration, the coolant purification flow rate is reduced (for example, the capacity is operated at 50% of the rated value) to suppress an increase in the heat load of the non-regenerative heat exchanger 6. It is also possible to do so. Further, when the regenerative heat exchanger 5 is bypassed, the high-temperature reactor water directly flows into the non-regenerated heat exchanger 6, resulting in a large temperature difference between the inlet and outlet of the heat exchanger, which is a severe condition in terms of thermal stress. Even in this case, there is no problem in soundness of the heat exchanger structure because it falls within the allowable limit in heat exchanger design.

The flow rate of the purification system is set to be constant both when the purified water is bypassed to the bypass pipe 30 and when the purified water is introduced to the regenerative heat exchanger 5, and the mass balance of water entering and leaving the reactor is bypassed. It is the same both in normal time and normal time, and no problems in reactor water level control will occur.

Further, at the time of startup of the reactor, the purification system bypasses the regenerative heat exchanger, so that the heat recovery of the extracted reactor water is not performed, resulting in a large heat loss in the heat balance of the reactor. However, the bypass of the regenerative heat exchanger does not cause a problem in the thermal efficiency of the plant, etc. because it is at a limited time when the reactor is started with a small amount of feed water.

FIG. 2 is a system diagram showing another embodiment of the reactor coolant purification system of the present invention.

In this embodiment, a bypass pipe 30 equipped with a bypass valve 20 and a regenerative heat exchanger inlet valve 21 are installed on the reheat side of the regenerative heat exchanger 5.

The method for controlling the opening and closing of the inlet valve 21 and the bypass valve 20 of the regenerative heat exchanger 5 is the same as that of the first embodiment, and the place where the bypass is performed is changed, and the low temperature purified return water is supplied to the water supply pipe 10 during the bypass. Inflow.

FIG. 3 is a system diagram showing an embodiment of the present invention.

In this embodiment, in addition to controlling the opening / closing of the regenerative heat exchanger inlet valve 21 and the bypass valve 20 by using the feed water flow meter 17, a pipe upper temperature meter 22 and a pipe upper temperature meter 22 are provided downstream of the confluence portion of the water supply pipe 10 with the purification system. A lower pipe thermometer 23 is installed and signals from both thermometers 22 and 23 are input to a temperature difference switch 24, and when the temperature difference between them is large, the regenerative heat exchanger 5 is bypassed. .

In other words, the OR of the low water supply flow rate and the large temperature difference between the upper and lower parts of the water supply pipe
The regeneration heat exchanger inlet valve 21 is closed by the (logical sum) signal,
An interlock for opening the bypass valve 20 is installed.

This guarantees the uncertainty regarding the disappearance of the stratified flow phenomenon in the water supply pipe, that is, the threshold for the water supply flow rate is, for example, about 20% or more of the rated flow rate. The stratified flow phenomenon can be surely prevented even if the threshold value varies due to the difference.

FIG. 4 shows a system diagram of the reference example.

In this reference example, instead of the water supply pipe upper thermometer and lower water thermometer shown in the embodiment of the present invention, a purification system pre-merging thermometer 25 and a water supply system pre-merging thermometer 26 are installed as shown and both thermometers are installed. Signals from 25 and 26 are input to the temperature difference switch 27, and control equipment is installed to bypass the regenerative heat exchanger when the temperature difference between them is large and the feed water flow rate is small. That is, when the temperature difference between the fluids that merge in the water supply pipe is small, regardless of the magnitude of the feedwater flow rate, the difference in density of the fluids is small and stratified flow phenomenon does not occur downstream of the junction, so the heat generated from the reactor is It is designed so that the thermal efficiency can be improved without unnecessary release to the outside.

〔The invention's effect〕

According to the present invention, since the low-temperature purified return coolant can be made to flow into the feedwater pipe system during the reactor start-up time when the feedwater flow rate of the feedwater pipe system is small, the supply water temperature and the purified return coolant are There is an effect that the temperature difference is eliminated and the stratified flow phenomenon can be prevented.

In particular, by using the temperature difference between the upper and lower temperature inside the pipe on the downstream side of the confluence point of the water supply pipe system as detection information, even if there is uncertainty in the disappearance of the stratified flow phenomenon due to only the water supply flow rate, the temperature difference is Since it can be bypassed when it gets bigger,
The heat generated from the nuclear reactor is not unnecessarily released to the outside, and the thermal efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of the present invention, FIG. 2 is a system diagram showing a second embodiment, FIG. 3 is a system diagram showing a third embodiment, and FIG. 4 is a fifth embodiment. Fig. 5 is a diagram showing the disappearance of the stratified flow phenomenon in the water supply pipe according to the present invention.
FIG. 5 (a) shows the relationship between the temperature of the water supply pipe and time, FIG. 5 (b) shows the relationship between the ratio of the water supply system flow rate and the purification system flow rate to the rated water supply flow rate and the time, and FIG. ) Indicates the relationship between the feed water temperature and the purification system temperature and time. FIG. 6 is a system diagram of a conventional purification device, FIG. 7 is a chart showing stratified flow development in a water supply pipe in the conventional purification device, and FIG. 7 (a) shows a relationship between the temperature of the water supply pipe and time. , FIG. 7 (b) shows the relationship between the ratio of the feed water and purified water to the rated flow rate and time, and FIG. 7 (c) shows the relationship between the feed water and purified water temperature and time. 1 ... Reactor, 2 ... Recirculation pump 3 ... Recirculation piping device, 4 ... Purification system pump 5 ... Regenerative heat exchanger, 6 ... Non-regenerative heat exchanger 7 ... Filtration desalination device 8 …… Non-regenerative heat exchanger cooling system 9 …… Main steam piping, 10 …… Water supply piping 11 …… Turbine, 12 …… Generator 13 …… Condenser, 14 …… Water pump 15 …… Water supply flow control valve , 16 …… Main steam flow meter 17 …… Supply water flow meter 18 …… Supply water flow control unit 19 …… Supply water flow switch 20 …… Regeneration heat exchanger bypass valve 21 …… Regeneration heat exchanger inlet valve 22 …… Water supply piping Upper thermometer 23 …… Water supply pipe lower thermometer 24 …… Temperature difference switch 25 …… Purification system before confluence thermometer 26 …… Water supply system before confluence thermometer 27 …… Temperature difference switch 28 …… Condenser blowdown valve 30 ... Bypass pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Mizutani 3-2-1, Sachimachi, Hitachi City, Ibaraki Hitachi Engineering Co., Ltd. (56) References JP-A-60-100095 (JP, A)

Claims (1)

[Claims] 1. A regenerative heat exchanger and a non-regenerative heat exchanger for cooling a reactor coolant, and a desalination device for purifying the coolant that has passed through the non-regeneration heat exchanger. After passing through the regenerated heat exchanger through the regenerated heat exchanger, the regenerated heat exchange is performed in the reactor coolant purification system that joins the feedwater piping system of the reactor and returns it into the reactor pressure vessel. Is provided with a bypass piping system, and is connected to a control circuit for inputting, as detection information, the temperature difference between the upper and lower sides of the piping downstream of the confluence point of the water supply piping system and the feed water flow rate of the water supply piping system, and the control circuit Is provided with switching means for switching the flow of the coolant to the bypass piping system based on the output signal from the control circuit, and the control circuit causes the stratified flow phenomenon to appear at the confluence of the purification system and the water supply piping system at the time of reactor startup. Setting value corresponding to range and detection Reactor coolant cleanup system for comparing the distribution is characterized by being configured to actuate said switching means.