JPH0679073B2 - Reactor coolant purification system - Google Patents

Description

The present invention relates to a reactor coolant purification system, and more particularly to a reactor coolant purification system configured to reduce radioactive contamination of a pump.

[Conventional technology]

Fig. 6 shows an outline of an example of the system configuration of a conventional boiling water reactor (hereinafter referred to as BWR). The BWR includes a recirculation system, a water supply system, a residual heat removal system, and a reactor coolant purification system which is the subject of the present invention.

Among them, the recirculation system is a system for returning the reactor water whose pressure is increased by the recirculation pump 2 (hereinafter referred to as a PLR pump) into the reactor pressure vessel 1 and forcibly circulating the reactor water.

The water supply system is a system in which steam generated in the pressure vessel 1 is caused to work in the turbine 9 and then condensed in the main condenser 10 to be condensed water to return the condensed water to the pressure vessel 1.

Cooling of the reactor when the reactor is stopped is performed by the main condenser 10 and the residual heat removal system. In other words, reactor cooling is performed by the main condenser 10 until the reactor pressure decreases from the normal operating pressure (about 70 kg / cm ² g) to the pressure at which the turbine gland seal does not work (about 9.0 kg / cm ² g). At a low pressure thereafter, it is performed by the residual heat removal system.

The residual heat removal system is always operated at a low pressure when the reactor is shut down, and the residual heat removal pump 3 is operated from the suction pipe side of the recirculation pump 2.
(Hereinafter referred to as "RHR pump") takes out reactor water, cools it with the residual heat removal system heat exchanger 4 by the reactor auxiliary cooling system, and then forms a closed loop for returning to the pressure vessel 1 through the discharge pipe of the PLR pump 2. It is a system for cooling the reactor.

The reactor coolant purification system is designed to operate the reactor pressure vessel 1 from high pressure during normal reactor operation (approximately 70.0 kg / cm ² g) to low pressure during reactor shutdown (up to 0 kg / cm ² g). It is a system that constantly operates over a wide range to purify reactor water. The reactor coolant purification system takes out reactor water from the suction piping side of the PLR pump 2 by the reactor coolant purification system pump 5 (hereinafter referred to as CUW pump), pressurizes it, and regenerates heat exchanger 6 and non-regeneration heat exchange. Bowl 7
After cooling to a predetermined temperature (about 50 ° C) with, the reactor water is purified with a purification device (filtration desalination device) 8, heated with the regenerative heat exchanger 6, and returned to the pressure vessel 1 via the water supply system. It is a system to return.

As for those related to the improvement of these systems, JP-A-55-
6260 and JP-A-54-38498.

[Problems to be solved by the invention]

The example of JP-A-55-6260 is composed of a heat exchanger, a pump, a purifying device and a bypass line of the device. During normal plant operation, the pump is operated at a small flow rate and the heat exchanger, pump and purifying device are used. The reactor water is returned to the reactor pressure vessel through the device and used as a coolant purification device. When the plant is stopped, the pump is operated at a large flow rate, and the reactor water is returned to the reactor pressure vessel via the heat exchanger, the pump, and the purifier bypass line, and used as a residual heat removal device.

Therefore, in this example, depending on the operating condition of the plant,
The same device will be used by switching to the coolant purifying device during normal operation and to the residual heat removing device when stopped. Here, the capacity of the reactor coolant purification system in the BWR is generally about 1/15 of the capacity of the residual heat removal system, which is a small flow rate. It is also possible that the flow velocity in the equipment becomes extremely slow and the piping and equipment are radioactively contaminated.

The residual heat removal device is used only at low pressure, but it is used as a coolant purification device at high pressure (about 70 kg
/ cm ² g), it is essential to make the entire device durable to use under high pressure.

On the other hand, as disclosed in JP-A-54-38498, C
The UW pump is installed on the downstream side of the heat exchanger and on the upstream side of the filter desalting device, and the temperature of the fluid inside the pump is lowered to reduce the oxide film generated on the inner surface of the pump, which absorbs it in the oxide film. It is considered to reduce the amount of cobalt 60 that is generated and to reduce the exposure dose of workers during regular inspections.

However, as shown in FIG. 7, the outlet side (F
The radiation dose on the inlet side (E section) is about 10 times higher than on the other side, and it is not possible to completely eliminate the contamination of the CUW pump. To completely eliminate the contamination of the CUW pump, it is sufficient to install the pump on the downstream side of the filter desalination device.However, the pump transfer increases the pressure loss on the pump inlet side. I couldn't do that because I had insufficient pushing pressure.

In addition, in FIG. 7, each part of A to F represents the position shown in FIG. That is, part A is the outlet side of the CUW pump, part B is the regenerative heat exchanger, part C is its outlet side, part D is the non-regenerative heat exchanger, part E is the purification device inlet side, and part F is the purification device outlet side. Is.

An object of the present invention is to provide a reactor coolant purification system that eliminates radioactive contamination of the CUW pump while sufficiently securing the pushing pressure on the inlet side of the CUW pump.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention installs a CUW pump of a purification system on the downstream side of a filter desalination apparatus, so as to make up the pumping pressure on the pump inlet side that is insufficient for that purpose, the reactor water to the purification system is supplemented. We propose a system configuration where the intake port is from the downstream side of the RHR pump and heat exchanger of the residual heat removal system.

The reactor water intake to the purification system may be on the downstream side of the PLR pump of the recirculation system.

[Action]

The reactor coolant purification system is always operated during normal reactor operation and during shutdown, but during shutdown, there is a risk of radioactive contamination of equipment due to flaking of cladding from fuel rods, etc. From the viewpoint of reducing the exposure of workers, it is particularly important to operate the reactor cleaning equipment when the reactor is shut down.

At low pressure when the reactor is shut down, the residual heat removal system including the RHR pump and heat exchanger is always operating to remove decay heat and residual heat of the reactor, but the conventional residual heat removal system has a cooling function. It was only for me. If the residual heat removal system is connected to the purification device of the reactor coolant purification system, the residual heat removal system will have both a so-called cooling mechanism and a purification function. Partial operation is unnecessary.

Here, the conventional arrangement of the CUW pump, heat exchanger, and purification device for the reactor coolant purification system is because the pump pressure or effective pump suction head (hereinafter referred to as NPSH) is insufficient when the reactor is shut down. The CUW pump is placed immediately after the reactor water is taken out from the reactor pressure vessel, as it may cause pump damage and damage the pump.
It was preventing PSH shortage. However, if the NPS deficiency of the purification system is supplemented from the residual heat removal system as described above, the problem of the CUW pump NPSH deficiency at the time of reactor shutdown can be solved. It can be done in the order of equipment and pump. For this reason, the CUW pump handles reactor water purified by the purification device, and radioactive contamination of the pump can be reduced.

Similarly, the shortage of NPSH can be compensated by the discharge pressure of the reactor coolant recirculation pump, and the same effect is expected.

〔Example〕

FIG. 1 shows an embodiment of the reactor cooling system purification system according to the present invention. In this embodiment, the heat exchangers 6, 7, the purifying device 8, and the CUW pump 5 are arranged in this order on the upstream side of the purifying device 8 of the purifying system, from the downstream pipe of the heat exchanger 4 of the residual heat removing system to the reactor water. A pipe 20 for intake is provided, a pipe 21 returning from the downstream pipe of the purification device 8 to the reactor pressure vessel 1 is connected, and switching valves 23, 24, 25 and the like are arranged.

To purify the reactor water during normal reactor operation, take the reactor water out of the pressure vessel 1, cool it with the reactor coolant purification system heat exchangers 6, 7, purify it with the purification device 8, and pressurize it with the CUW pump 5. The heating is performed in the reactor cleaning system heat exchanger 6 and then returned to the pressure vessel 1 again.

When the reactor is shut down, the residual heat removal system operates in the same manner as in the past to cool the reactor. Purification of reactor water is performed by the residual heat removal system.
A part of the reactor water whose pressure is increased and cooled by the RHR pump 3 and the heat exchanger 4 is introduced into the purification device 8 by the connection pipe 20 and purified, and is returned into the pressure vessel 1 by the return pipe 21. Therefore, in this embodiment, during normal reactor operation, the reactor water can be purified as in the conventional case, and when the reactor is stopped, only the residual heat removal system is operated without operating the reactor coolant purification system pump and the like. By itself, both cooling function and purification function can be obtained.

As already mentioned, in the conventional reactor coolant purification system, CU
When the W pump is placed on the downstream side of the purifier, the pressure is high (about 70.0 kg / cm ² g) in the pressure vessel 1 during normal reactor operation, and sufficient pushing pressure can be obtained on the suction side of the pump 5. There was no problem with NPSH of Pump 5. However, when the reactor is at a low pressure, the pressure loss required by the CUW pump 5 is insufficient due to the pressure loss in the heat exchangers 6, 7 and the purification device 8 on the upstream side of the pump 5, and the pump 5 causes cavitation. There was a problem of lack of NPSH of pump 5. Therefore, in order to secure the NPSH of the CUW pump 5, the conventional reactor cleaning equipment is designed as shown in FIG.
5, the heat exchangers 6, 7 and the purification device 8 are arranged in this order.

On the other hand, in the present embodiment, when the reactor is at a low pressure, the pump pressure of the residual heat removal system is used to purify the reactor water, so that the problem of NPSH shortage of the pump 5 is solved. As shown, the heat exchangers 6, 7, the purifier 8, and the pump 5 can be arranged in this order. As a result, the pump 5 does not directly handle the reactor water taken out from the reactor pressure vessel 1,
The radioactive contamination of the CUW pump 5 is reduced.

According to FIG. 7 which shows the outline of the pipe surface dose rate of the conventional reactor coolant purification system, the downstream side of the purification device 8 (F section) is about 10% smaller than the upstream side of the regenerative heat exchanger 6 (A section). It turns out that it is about 1/100. In the present embodiment, the radioactive contamination of the pump 5 can be reduced to about 1/100 by disposing the purification device 8 on the downstream side.

Further, since the reactor coolant purification system pump 5 heat exchangers 6 and 7 can be stopped when the reactor is stopped, the valves 23, 24 and 25 can be closed to isolate them and the equipment can be easily inspected.

Another embodiment of the present invention is shown in FIGS.

FIG. 2 shows the connection pipe 20 from the residual heat removal system heat exchanger 4 connected to the upstream side of the reactor coolant purification system regenerative heat exchanger 6. Since it passes through the heat exchangers 6 and 7 when the reactor is shut down,
The cooling function is improved.

FIG. 3 shows the connection pipe 20 from the two-system residual heat removal system heat exchanger 4 connected to the reactor coolant purification system.

FIG. 4 shows a modification in which the heat exchangers 6, 7 and the CUW pump 5 of the reactor coolant purification system are deleted and only the connecting pipe 20, the purifying device 8 and the return pipe 21 are provided. In this embodiment, the reactor coolant purification system cannot be operated during normal reactor operation. However, there are usually other purification systems, and the expected purification contribution rate of this purification system is about 2%. Also, the cladding etc. targeted by this purification system are separated when the reactor is stopped. Considering that it is easy to get out, it can be said that the system structure that operates only when stopped is sufficiently significant.

Next, an embodiment of the invention using a recirculation system instead of the residual heat removal system used in the above embodiments will be described with reference to FIG.

In this embodiment, the reactor water to be purified is taken in from the downstream of the PLR pump 2. In the figure, 15 is a stop valve for pump maintenance, 16 is a flow control valve, 17 is a bypass valve, and 18 is a water supply system piping.

The reactor water in the nuclear reactor 1 is circulated by the PLR pump 2. A part of this is cooled to about 50 ° C. in the regenerative heat exchanger 6 and the non-regenerative heat exchanger 7 after the flow rate is adjusted by the flow rate adjusting valve 16,
Purified by the purifying device 8. The purified water is pressurized by the reactor coolant purification system CUW pump 5 and returned to the reactor 1 through the regenerative heat exchanger 6 and the water supply system pipe 18.

The fluid flowing through the CUW pump 5 of the present embodiment is purified water in which radioactive substances such as cobalt 60 have been adsorbed by the purifying device 8. Therefore, the CUW pump 5 does not adsorb radioactive substances in the oxide film on the inner surface of the pump, and can reduce the exposure dose of the worker who regularly inspects the pump 5.

Next, a specific operation example of the device shown in FIG. 5 will be described.

(A) When the reactor pressure is low In the conventional example, since the reactor coolant purification system was connected to the upstream side of the PLR pump 2, the suction pressure of the CUW pump 5 was
It is expressed as follows.

(Pump suction pressure) = (Reactor dome pressure) + (Head from reactor water level to CUW pump installation position)-(Piping pressure loss)-(Heat exchanger pressure loss)-(Filtration desalination unit pressure loss) ... (1) In the currently designed pump, the suction pressure is 0.6 kg / cm
If it is less than ² g, cavitation occurs inside the pump, and the inside of the pump casing and the pump blades are damaged. In the operation mode of the plant, NPSH cannot satisfy this condition when the plant is stopped (when the reactor pressure is atmospheric pressure), and the pressure is insufficient at about 0.5 kg / cm ² g, and the purification operation Can't continue. However, the reactor coolant purification system is a system in which purification of reactor water must be continued not only during reactor operation but also during shutdown.

In the present invention, this problem is solved by utilizing the discharge pressure of the PLR pump 2 as shown in FIG. In this case, the pump suction pressure is the expression (1) plus (PLR pump discharge pressure).

The PLR pump 2 is constantly operating not only during plant operation but also during plant stoppage at a rated speed of approximately 20%, and the discharge pressure of this pump 2 is approximately 0.6 kg / cm ² g (20% When rotating).

Therefore, according to the present invention, the suction pressure required for operating the CUW pump 5 can be secured even when the plant is stopped (at the reactor pressure atmospheric pressure).

(B) When the recirculation pump is operating at the rated speed When the reactor pressure is high and the reactor is operating at the rated output, PL
The R pump 2 is operated at the rated speed. In this case, the PLR pump discharge pressure is about 18 kg / cm ² g, which is sufficiently higher than the system pressure loss (sum of pressure loss of piping equipment) of the reactor coolant purification system of about 12 kg / cm ² g. System is CU
It is possible to operate by stopping the W pump 5 and opening the pump bypass valve 17.

Further, the flow rate of the reactor coolant purification system is only 1 to 2% of the flow rate of the reactor coolant recirculation system, and even if the purification flow rate is secured by the PLR pump 2, the motor output of the pump 2 is maintained. It does not affect.

Therefore, according to the present invention, the CUW pump 5 is operated during plant operation.
Can be stopped.

(C) When Purifying Reactor Water During CUW Pump Maintenance In this example, the inlet for the reactor coolant purification system was
By installing it between the PLR pump 2 and the stop valve 15, the purifying operation of the reactor water can be continued even during the maintenance of the CUW pump 5.

When inspecting the CUW pump 5, the inlet / outlet valve 25 of the pump 5 is closed and the bypass valve 17 is opened. The flow rate of the system can be secured by the pump 2 by closing the outlet stop valve 15 of the PLR pump 2.

Since the PLR pump 2 is a large-capacity high-pressure type pump, in order to secure the reactor coolant purification system flow rate and pressure, increase the pump rotation speed to about 70% of the rating to secure the pressure, and the flow rate is The throttle valve 16 must be throttled.

Here, since the time required for the mechanical seal inspection of the PLR pump 2 is shorter than the number of days required for the maintenance of the CUW pump 5, the purifying operation time of the reactor water can be extended by the present invention.

However, the required power for operating the PLR pump 2 at 70% of the rated speed is much higher than the power required for the rated operation of the CUW pump 5, so this operating mode is used for pump 5 maintenance. It is necessary to switch the operation for each of the above-mentioned operation modes A to C, which is not preferable in terms of economic efficiency if it is used at other times.

According to the present invention, as shown in FIG.
The dose of (part) can be reduced to about 1/100 of the dose in part A of the conventional example.

〔The invention's effect〕

According to the present invention, the problem of insufficient pushing pressure is solved, and the CU
Since the W pump can be installed on the downstream side of the filter demineralizer, the following effects can be obtained.

(1) The radioactive material accumulated inside the CUW pump can be reduced to about 1/100 of that of the conventional method, and the exposure dose to workers during regular inspections can be reduced.

(2) During the plant operation, reactor water can be supplied to the purifier using the PLR pump discharge pressure, and the CUW pump can be stopped, so the pump does not become contaminated.

(3) RHR pump or PLR during CUW pump maintenance
The pump can continue to operate the purification system.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a reactor coolant purification system using a residual heat removal system pump according to the present invention, FIG.
FIG. 3 is a system diagram showing another embodiment, FIG. 4 is a system diagram showing a modification of the embodiment shown in FIG. 1, and FIG. 5 is a reactor coolant purification using a recirculation pump according to the present invention. FIG. 6 is a system diagram showing an example of a system, FIG. 6 is a system diagram showing an example of a general system configuration of a conventional BWR, and FIG. 7 is a graph showing an example of pipe surface dose rate in the coolant purification system. . 1 ... Reactor pressure vessel, 2 ... Recirculation (PLR) pump, 3 ...
Residual heat removal (RHR) pump, 4 ... Residual heat removal system heat exchanger, 5 ... Reactor coolant purification system (CUW) pump, 6 ... Regenerative heat exchanger, 7 ... Non-regenerated heat exchanger, 8 ... Purification device , 9 ... Turbine, 10 ... Main condenser, 15 ... Pump maintenance stop valve, 16 ... Flow control valve, 17 ... Bypass valve, 18 ... Water supply system piping, 20 ... Reactor water intake piping, 21 ... Return piping, 23 , 24,25 ... Switching valve.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tadashi Shiraishi 1-1-1, Sachimachi, Hitachi City, Ibaraki Hitachi Ltd., Hitachi Works (72) Inventor Shoichiro Kinoshita 3-chome, Hitachi City, Ibaraki Prefecture 1-1 Hitachi Ltd., Hitachi Works, Hitachi Plant (72) Inventor Minoru Okura 3-1-1, Saichocho, Hitachi City, Ibaraki Prefecture Hitachi Ltd., Hitachi Works, Hitachi Plant (72) Inventor Akio Tsuji Hitachi City, Ibaraki Prefecture 3-1, 1-1 Sachimachi, Hitachi, Ltd. Hitachi factory (56) References JP-A-54-38498 (JP, A) JP-A-60-17396 (JP, A) JP-A-62-180295 ( JP, A) JP 62-190496 (JP, A)

Claims (5)

[Claims] 1. A reactor pressure vessel, which includes a pump, a heat exchanger, and a purifying device, takes in reactor water from a suction pipe side of a recirculation pump of a recirculation system during normal operation of the reactor, cools it to a predetermined temperature, and purifies it. In the reactor coolant purification system to be returned, the pump of the purification system is arranged downstream of the purification device, and the reactor is installed from the outlet side of the residual heat removal system pump instead of the suction pipe side of the circulation pump when the reactor is stopped. A reactor coolant purification system characterized by the provision of piping for introducing water. 2. A reactor coolant purification system according to claim 1, wherein a reactor water intake pipe when the reactor is shut down is connected to the heat exchanger inlet upstream of the purification device. . 3. The reactor coolant purification system according to claim 1, wherein the residual heat removal system has two systems and the reactor water intake pipe is connected from both systems. 4. The nuclear reactor according to claim 1, further comprising a switching valve for disconnecting the purification system pump from the system when the reactor is stopped. Coolant purification system. 5. A reactor coolant purification system, which includes a pump, a heat exchanger, and a purification device, cools reactor water taken from a recirculation system to a predetermined temperature, purifies it, and then returns it to a reactor pressure vessel,
A switching valve is arranged in front of and behind the purification system pump and valves for bypassing this pump are provided in parallel during normal reactor operation, and these are arranged downstream of the purification device, and the reactor water to the heat exchanger is also provided. A reactor coolant purification system characterized in that an intake pipe is connected downstream of a recirculation system pump through a valve that regulates a flow rate when the reactor is stopped.