JPS62215894A - Purification system of coolant for 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 [Industrial Application Field] The present invention relates to a nuclear reactor coolant purification system, and particularly to a nuclear reactor coolant purification system configured to reduce radioactive contamination of a pump.

[Conventional technology]

Figure 6 shows an outline of an example of the system configuration of a conventional boiling water reactor (hereinafter referred to as BWR).
It is equipped with a water supply system, a residual heat removal system, and a reactor coolant purification system, which is the object of the present invention.

Among these, the re@ring system is the recirculation pump 2 (hereinafter referred to as the recirculation pump 2).

This is a system in which reactor water pressurized by a PLR pump is returned to the reactor pressure vessel 1 for forced circulation.

The water supply system supplies steam generated in the pressure vessel 1 with a turbine 9.
3 (after doing so, it is condensed in the main condenser 10 as condensate,
This system returns condensate to the pressure vessel 1.

Reactor cooling during reactor shutdown is performed by the main condenser 10 and the residual heat removal system. In other words, reactor cooling is carried out when the reactor goes from its normal operating pressure (approximately 70 kg/cJg) to the pressure at which the turbine gland seal becomes ineffective (approximately 9.0 kg/Jg).
g) is carried out by the main condenser 10, and thereafter by the residual heat removal system when the pressure is low.

The residual heat removal system operates constantly when the pressure is low when the reactor is shut down, and connects the suction pipe of the recirculation pump 2 to the residual heat removal pump 3 (
A closed loop is constructed in which reactor water is taken out by the RHR pump (hereinafter referred to as the RHR pump), cooled by the reactor auxiliary equipment cooling system by the residual heat removal system heat exchanger 4, and then returned to the pressure vessel 1 via the discharge piping of the PLR pump 2. , is a system that cools the yK sub-reactor.

The reactor coolant purification system has a wide range of pressure inside the reactor pressure vessel 1, from high pressure during normal reactor operation (approximately 70.0 kg/cx1g) to low pressure during reactor shutdown (~Okg/dg). This is a system that operates continuously throughout the entire period to purify reactor water. The reactor coolant purification system extracts reactor water from the suction pipe side of the PLR pump 2 using a reactor coolant purification system pump 5 (hereinafter referred to as CUW pump), pressurizes it, and transfers it to a regenerative heat exchanger 6 and a non-regenerative heat exchanger. Set the temperature in the container 7 (approx. 50℃)
After cooling until.

In this system, reactor water is purified by a purification device (filtration salting device) 8, heated by the regenerative heat exchanger 6, and returned to the positive pressure vessel 1 via the water supply system.

Regarding the improvement of these systems, Japanese Patent Application Laid-Open No. 55
-6260, JP-A No. 54-38498, etc.

[Problem that the invention seeks to solve]

The example disclosed in JP-A-55-6260 consists of a heat exchanger, a pump, a purification device, and a bypass line for the device.During normal plant operation, the pump is operated at a small flow rate, and the heat exchanger, pump, purification device Reactor water is returned to the reactor pressure vessel through the system and is used as a coolant purification system. When the plant is shut down, the pump is operated with a large discharge, and reactor water is returned to the reactor pressure vessel via the heat exchanger, pump, and purification device J<Ipass line, where it is used as a residual heat removal device.

Therefore, in this example, depending on the operating state of the plant,
The same device is used as a coolant purification device during normal operation, and when stopped N:
In some cases, it is necessary to switch to a residual heat removal device. Here, the capacity of the reactor coolant purification system in the BWR is generally a small flow rate, about 1/J5 of the capacity of the residual heat removal system, so when used as a coolant purification system in this example, the piping The flow rate inside the equipment will be extremely slow, and the piping and equipment may be contaminated with radioactivity.

In addition, it is used as a residual heat removal device only when the pressure is low, but as a coolant purification device during normal operation it is used at high pressure (approximately 70k).
g/ff1g), so it was impractical to make the entire device capable of withstanding use at high pressures.

On the other hand, as shown in Japanese Patent Application Laid-Open No. 54-38498, a CUW pump is placed i12 downstream of a heat exchanger and upstream of a filtration chlorination device to lower the temperature of the fluid inside the pump. It is being considered to reduce the amount of cobalt-60 that is absorbed into the oxide film by reducing the amount of oxide film that forms on the inner surface of the pump, thereby reducing the amount of radiation that workers are exposed to during periodic inspections.

However, the radiation dose on the inlet side (section E) is about 10 times higher than on the outlet side (section F) of the pumping device 3 shown in Fig. 7, and it is not possible to completely eliminate contamination of the CUW pump. In order to completely eliminate contamination of the CUW pump, which is not a problem, it is possible to install the pump downstream of the filtration/desalination equipment, but relocating the pump increases the pressure loss on the pump inlet side. This could not be done because the pushing pressure on the inlet side would be insufficient.

In addition, in FIG. 7, each part of A-F represents the position shown in FIG. That is, part A is the outlet side of the CUW pump, and part B is the regenerative heat exchanger.

Section 6 is the outlet side, section D is the non-regenerative heat exchanger, section E is the inlet side of the purifier, and section F is the outlet side of the purifier.

An object of the present invention is to provide a reactor coolant purification system that eliminates radioactive contamination of the CUW pump while ensuring sufficient pumping pressure on the artificial side of the CUW pump.

[Means for solving problems]

In order to achieve the above object, the present invention provides CUW of purification system.
Install the pump downstream of the filtration and desalination equipment.

Therefore, in order to compensate for the insufficient pushing pressure on the pump inlet side, the reactor water intake to the purification system was connected to the RHR of the residual heat removal system.
We propose a system configuration starting from the downstream side of the pump and heat exchanger.

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

[Effect]

The reactor coolant purification system is in constant operation during normal reactor operation and during shutdown, but when the reactor is shut down, there is a risk of radioactive contamination of equipment due to flaking of crud from the fuel rods, so plant periodic In terms of reducing the exposure of working tools during inspections, it is especially important to operate the reactor purification equipment when the reactor is shut down.

At low pressure when the reactor is shut down, the decay heat of the reactor.

In order to remove residual heat, a residual heat removal system including an RHR pump and a heat exchanger is in constant operation.The residual heat removal system used in the past had only a cooling function. If the residual heat removal system is connected to the purification equipment of the reactor coolant purification system, the residual heat removal system will have both a cooling function and a purification function. There is no need to operate the parts.

Here, the arrangement of the CUW pump, heat exchanger, and purification device in the conventional reactor coolant purification system is based on the pump pressure or the effective pump suction head (hereinafter referred to as NP) when the reactor is shut down.
Because there was a risk of cavitation occurring inside the pump and damaging the pump due to a shortage of SH), a CUW pump was placed immediately after reactor water was removed from the reactor pressure vessel to prevent a pump NPSH shortage. . However, as mentioned above, if the residual heat removal system compensates for the NPSH shortage in the purification system, the problem of CUW pump NPSH shortage at the time of reactor shutdown will be solved, so the arrangement of the reactor purification system can be changed to a heat exchanger, purification system, etc. This can be done in the following order: equipment and pump. Therefore, the CUW pump handles reactor water that has been purified by the purification device, and radioactive contamination of the pump can be reduced.

Furthermore, the shortage of NFSH can be similarly compensated for by the reactor coolant recirculation pump discharge pressure, and similar effects are expected.

〔Example〕

An embodiment of the reactor cooling system purification system according to the present invention is shown in FIG. 1. In this embodiment, heat exchangers 6, 7. Purification device8. C.U.
A pipe 20 for taking in reactor water from the downstream pipe of the heat exchanger 4 of the residual heat removal system is provided upstream of the purification device 8 of the purification system arranged in the order of the W pump 5, and Connect the pipe 21 returning to the reactor pressure vessel 1, and connect the switching valve 23.
, 24°25, etc.

To purify reactor water during normal reactor operation, reactor water is taken out from the pressure vessel 1, cooled by the reactor coolant purification system heat exchanger 6.7, purified by the purification device 8, and pressurized by the CUW pump 5. , heated in the R sub-furnace purification system heat exchanger 6 and returned to the pressure vessel 1 again.

When the reactor is shut down, the residual heat removal system is operated in the same manner as before to cool the reactor. Purification of reactor water.

A portion of the reactor water that has been pressurized and cooled by the RHR pump 3 and heat exchanger 4 of the residual heat removal system is transferred to the purifier I! through the connecting pipe 20!
8 for purification and return to the pressure vessel 1 through a return pipe 21. Therefore, in this embodiment, during normal reactor operation, reactor water can be purified as before, and when the yX subreactor is shut down, only the residual heat removal system is operated without operating the pumps of the reactor coolant purification system. This provides both cooling and purification functions.

As mentioned above, in conventional reactor coolant purification systems,
When the CU W pump is placed downstream of the purification equipment, high pressure (approximately 70.0 k
g/ff1g), and sufficient pushing pressure was obtained on the suction side of the pump 5, so there was no problem with the NPSH of the pump 5. However, when the reactor is shut down and the pressure is low, the pump 5
Upstream heat exchanger 6.7. Due to the pressure loss in the purifier 8, the pushing pressure required for the CUW pump 5 is insufficient.

There was a risk that cavitation would occur in pump 5, and there was a problem of insufficient NPSH in pump 5. Therefore, in the conventional nuclear reactor purification equipment, in order to ensure the NPSH of the CUW pump 5, as shown in FIG. heat exchanger 6,
7. The equipment is arranged in the order of purification equipment fi8.

On the other hand, in this embodiment, when the reactor is stopped and the pressure is low, the reactor water is purified using the pump pressure of the residual heat removal system, so the problem of insufficient NPSH in the pump 5 is solved, and as shown in FIG. As shown, heat exchange @6,7. Purification device8. The devices can be arranged in the order of pump 5. As a result, the pump 5 is
Since the reactor water taken out from the reactor pressure vessel 1 is no longer handled directly, radioactive contamination of the CUW pump 5 is reduced.

According to FIG. 7, which shows an outline of the pipe surface dose rate of a conventional reactor coolant purification system, the downstream side of the purification device 8 (section F) is approximately In this example, the purification device t! is found to be about 1/100. 8 downstream arrangement, the radioactive contamination of the pump 5 can be reduced to about 17,100.

Furthermore, since the reactor coolant purification system pump 5 and heat exchanger 6.7 can be stopped when the reactor is shut down, the valves 23, 24, and 25 can be closed to isolate them and the equipment can be easily inspected.

Other embodiments of the invention are shown in FIGS. 2 and 3.

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

FIG. 3 shows connecting pipes 20 from two residual heat removal system heat exchangers 4 connected to a reactor coolant purification system.

Figure 4 shows the reactor coolant purification system heat exchanger 6°7, CU
Delete W pump 5 and connect piping 20. Purification device8. This is a modification example in which only the return pipe 21 is used.

In this example, the reactor coolant purification system cannot be operated during normal reactor operation. However, there are other systems that are normally purifying, and the expected purification contribution rate of this purification system is Considering that it is about 2%, and that the crud that this purification system targets tends to flake off and come out when the reactor is shut down, it can be said that there is sufficient significance in a system configuration that operates only when the reactor is shut down. .

Next, an embodiment of the invention in which a recirculation system is used in place of the residual heat removal system used in the previous embodiments will be described with reference to FIG.

In this embodiment, the reactor water to be purified is the PLR pump 2
taken in from downstream. In fig.

15 is a pump maintenance stop valve, 16 is a flow rate adjustment valve, 17 is a bypass valve, and 18 is a water supply system piping.

Reactor water within the nuclear reactor 1 is circulated by a PLR pump 2. After adjusting the flow rate with the flow rate adjustment valve 16, a part of this is transferred to the regenerative heat exchanger 6. It is cooled to about 50° C. in the non-regenerative heat exchanger 7 and purified in the purifier 8. The purified water is pressurized by the reactor coolant purification system CUW pump 5, and then passed through the regenerative heat exchanger 6. The water is returned to the reactor 1 via the water supply system piping 18.

The fluid flowing through the CUW pump 5 of this embodiment is the purifier 8
This is purified water that has been treated to adsorb radioactive substances such as cobalt-60. Therefore, the CUW pump 5 does not adsorb radioactive substances in the oxide film on the inner surface of the pump, and the amount of radiation exposure of workers who periodically inspect the pump 5 can be reduced.

Next, a specific example of the operation of the apparatus shown in FIG. S will be explained.

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

(Pump suction pressure) = (M child reactor dome pressure) + (wood head from reactor water level to CUW pump installation position) - (piping pressure loss) - (heat exchanger pressure loss) - (filtration desalination equipment pressure loss) (1) In the currently designed pump, the above suction pressure is 0.6
If it is less than kg/ff1g, cavitation will occur inside the pump, causing damage to the inside of the pump casing and the pump blades. Among the plant operation modes, NPSH cannot satisfy this condition when the plant is stopped (when the R reactor pressure is atmospheric pressure), which is about 0.
Due to a pressure shortage of 5 kg/cdg, purification operation could not be continued. However, the JJa reactor coolant purification system
This system requires continuous purification of reactor water not only during reactor operation but also when the reactor is shut down.

In the present invention, this problem is solved by utilizing the discharge pressure of the PLR pump 2 as shown in FIG.

The pump suction pressure in this case is the sum of equation (1) plus (PLR pump discharge pressure).

The PLR pump 2 continues to operate at approximately 20% of the rated rotation speed not only during plant operation but also when the plant is stopped, and the discharge pressure of this pump 2 is approximately 0.6 kg /
ci g (at 20% rotation).

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

(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 power, the PL
The R pump 2 is operated at the rated rotation speed. In this case, the PLR pump discharge pressure is approximately 18 kg/cIig, which sufficiently exceeds the system pressure loss (sum of pressure loss of piping equipment) of the yK subreactor coolant purification system, which is approximately 12 kg/cd g. , the CUW pump 5 is stopped and the bypass valve 17 of the pump is opened to allow operation.

Further, the flow rate of the reactor coolant purification system is only 1 to 2% of the flow rate of the m reactor coolant recirculation system.

Even if the purification flow rate is secured by PLR pump 2, pump 2
does not affect the motor output.

Therefore, according to the present invention, the cUv pump 5 can be stopped during plant operation.

(C) When purifying reactor water during CUW pump maintenance In this embodiment, by installing the intake of the reactor coolant purification system between the PLR pump 2 and the stop valve 15,
Reactor water purification operation can be continued even during maintenance of the UW 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 ensured by the pump 2 by closing the outlet stop valve 15 of the PLR pump 2.

Since PLR pump 2 is a large-capacity, high-pressure pump, in order to secure the reactor coolant purification system flow rate and pressure, the pump rotation speed is increased to about 70% of the rated value to secure the pressure, and the flow rate is Throttle operation must be performed using the regulating valve 16.

Here, since the time required to inspect the mechanical seal of the PLR pump 2 is shorter than the number of days required for maintenance of the CV W pump 5, the present invention can extend the reactor water purification operation time.

However, the power required to operate the PLR pump 2 at 70% of the rated rotation speed is much larger than the power required for the rated operation of the C, UW pump 5, so this operation mode is Operation mode A mentioned above is unfavorable from an economical efficiency point of view if it is used for purposes other than maintenance.
- It is necessary to switch the operation for each C.

According to the present invention, as shown in FIG. 7, the dose on the outlet side (F section) of the purifier is approximately 1/100 of the dose on the A section of the conventional example.
can be reduced to

〔Effect of the invention〕

According to the present invention, the problem of insufficient pushing pressure is solved, and C
Since the UW pump can be installed downstream of the salt filter, the following effects can be obtained.

(1) Radioactive materials accumulated inside the CUW pump can be reduced to about 1/100 compared to conventional pumps, reducing the number of workers exposed to radiation during regular inspections.

(2) During plant operation, reactor water can be supplied to the purification equipment using the PLR pump for discharge expansion, and the CUW pump can be stopped, so no contamination of the pump occurs.

(3) During maintenance of the C1JW pump, the purification system can continue to operate with the RHR pump or PLR pump.

[Brief explanation 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. 2;
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, FIG. 5 is a system diagram showing an embodiment of a reactor coolant purification system using a recirculation system pump according to the present invention, and FIG. is conventional BWR
FIG. 7 is a system diagram showing an example of a general system configuration, and FIG. 7 is a graph showing an example of the piping surface i amount ratio 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-regenerative heat exchanger, 8... purification device, 9... turbine, 1
0... Main condenser, 15... Stop valve for pump maintenance, 16... Flow rate adjustment valve, 17... Bypass valve,
18... Water supply system piping, 20... Reactor water intake piping, 2
1...Return piping, 23, 24.25...Switching valve.

Claims (1)

[Claims] 1. During normal operation of the reactor, which includes a pump, a heat exchanger, and a purification device, reactor water is taken in from the suction pipe side of the recirculation pump of the recirculation system, cooled to a predetermined temperature, purified, and then released into the reactor. In the reactor coolant purification system that returns the reactor coolant to the pressure vessel, the purification system pump is placed downstream of the purification device, and when the reactor is shut down, the outlet of the residual heat removal system pump is placed in place of the suction piping side of the circulation pump. A reactor coolant purification system characterized by having piping that takes in reactor water from the side. 2. A reactor coolant purification system according to claim 1, characterized in that a reactor water intake pipe at the time of reactor shutdown is connected to the inlet of the heat exchanger upstream of the purification device. 3. A reactor coolant purification system according to claim 1 or 2, characterized in that there are two residual heat removal systems, and the reactor water intake piping is connected from both systems. 4. A nuclear reactor coolant purification system according to any one of the above claims, further comprising a switching valve that disconnects the pump of the purification system from the system when the reactor is shut down. 5. In a reactor coolant purification system that includes a pump, a heat exchanger, and a purification device and returns reactor water taken in from both circulation systems to a predetermined temperature and purified, and then returned to the reactor pressure vessel, the purification system pump Switching valves are placed before and after the reactor, and valves that bypass this pump during normal reactor operation are provided in parallel, and these are placed downstream of the purification device, and the reactor water intake piping to the heat exchanger is connected to the reactor. A nuclear reactor coolant purification system, characterized in that it is connected downstream of a recirculation system pump via a valve that adjusts the flow rate during shutdown.