JPS6189591A - Purifier for coolant of 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] [Field of Application of the Invention] The present invention relates to a reactor coolant purification system, which is effective in reducing radiation exposure of workers during pump maintenance and inspection, in particular. Regarding system configuration.

[Background of the invention]

The conventional reactor coolant purification system, as shown in Figure 3,
Some of the reactor coolant was removed from the suction pipe of recirculation pump 2)
After that, the pressure is increased in the circulation bottle/pro, and the temperature is cooled to approximately SOC in the regenerative heat exchanger 4 and the non-regenerative heat exchanger 5.
The reactor pressure vessel 1 is returned to the reactor pressure vessel 1 via the water supply pipe 8. In the non-regenerative heat exchanger 5, auxiliary cooling water is passed through a pipe 9 to the shell side, and the high-temperature coolant flowing on the pipe side is cooled by heat exchange. In the conventional purification device configured in this way, the Co-60 generated in the nuclear reactor is
Corrosion product nuclides such as +Co-58 circulate together with the coolant through piping systems and equipment, and adhere to parts of the piping systems and equipment that come into contact with the coolant. Therefore, there was a problem in that maintenance and inspection workers were exposed to gamma rays emitted from these radionuclides. Furthermore, when comparing the radiation dose rate of the piping system and equipment upstream and downstream of the heat exchangers 4 and 5, on the upstream side where the coolant temperature is about 280C compared to the downstream side where the coolant temperature is about 50C, It was confirmed during regular inspections of the actual equipment that the radiation dose rate was extremely high. In particular, the circulation pump 6 installed on the upstream side requires a high degree of maintenance and inspection, and has a complicated structure that tends to take a long time to work, which tends to increase the radiation exposure of workers. Countermeasures are being taken to combat this, such as installing radiation shields using lead or other materials, but these are not sufficient.

FIG. 4 is an example of another conventional technology, a low-pressure reactor purification system. This device is a desalination device 1 that operates under low pressure conditions.
6, it is necessary to install a pressure reducing valve 17 upstream thereof to reduce the pressure to about 10/9/i. For this reason,
A circulation pump 6 is installed downstream of the desalination device 16 in order to return the purified coolant to the high-pressure reactor pressure vessel. Further, on the upstream side of the circulation pump 6, a regenerative heat exchanger 4. Non-regenerative heat exchanger5. Pressure reducing valve 17. Filtration desalination equipment7. Desalination equipment 1
6 is installed, and the pressure loss up to the circulation pump 6 is extremely low. When the reactor pressure drops to about 10 kg/cm, the pushing pressure of the circulation pump 6 (NPSH
) may be insufficient and cavitation may occur. In order to prevent this, an auxiliary pump 18 is installed upstream of the regenerative heat exchanger 4.

In this conventional device, the circulation pump 6 is installed downstream of the heat exchanger 4.5, so as mentioned above, the coolant temperature is low and the amount of radioactive corrosion products deposited is small, but the auxiliary pump 18 A similar problem occurs with this auxiliary pump 18 because it is installed on the upstream side.

FIG. 5 shows the device described in Japanese Patent Application Laid-open No. 1@54-38498. This device is an example in which the circulation pump 6 is installed downstream of the non-regenerative heat exchanger 5 for the purpose of lowering the temperature of the coolant flowing into the circulation pump 6 to extend the life of the pump mechanical seal. Furthermore, in order to prevent the circulation pump from running out of NFSH when the reactor pressure becomes low, a bypass pipe 19 is installed that connects the discharge pipe of the recirculation pump 2 to the regenerative heat exchanger inlet pipe 3. Open valve 20 and open valve 21
is closed, and the refrigerant is passed through the device at the discharge pressure of the recirculation pump 2 to ensure the NPSH of the circulation pump. Since this device does not have an auxiliary pump like the low-pressure reactor coolant purification device shown in FIG. 4, there is no fear of radioactive corrosion products adhering to this pump. However, since the recirculation pump 2 is stopped when the nuclear reactor is shut down, this device cannot be operated, and there is a problem that it is impossible to purify the coolant while the reactor is shut down.

In addition, there are other publications related to the reactor coolant purification system of the present invention, such as JP-A-54-20294 and JP-A-56.
-111496 etc.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art, reduce the amount of radiation exposure of workers during maintenance and inspection of circulation pumps, and provide NFS of circulation pumps even when the reactor is shut down or at low pressure.
It is an object of the present invention to provide a reactor coolant purification system having a configuration that can sufficiently secure H.

[Summary of the invention]

FIG. 6 shows the experimental results of the relationship between the amount of radioactive corrosion products deposited, that is, the surface dose rate, and the coolant temperature.

This figure was calculated from experimental data published in the following literature. E, G, Brush and W,
L.

pearl @Corrosion and Corr
osion Product'3eleasein N
eutral Feedwater 'Corrosi'
on.

28.129 (1972). The reactor coolant temperature in a BWR plant is usually around 280C, and the amount of radioactive product deposited at this temperature is extremely large. In comparison, when the coolant temperature at the outlet of the non-regenerative heat exchanger is about 50C, the amount of radioactive products adhering to it was found to be very small, about 1/10. When the surfaces of piping systems and equipment corrode, the higher the temperature of the coolant, the thicker the oxide film becomes, so it is presumed that radioactive products are more likely to be absorbed into the oxide film. Based on the above findings, the reactor coolant purification system of the present invention is characterized in that a circulation pump is installed downstream of the non-regenerative heat exchanger where the coolant temperature is as low as about 50C.

Next, by installing the circulation pump downstream of the non-regenerative heat exchanger, the circulation pump NP is activated during reactor shutdown and low pressure.
Measures to prevent SH from running out are described below. If a circulation pump is installed downstream of a non-regenerative heat exchanger, the pressure loss in the heat exchanger and piping will be about 2 compared to installing it upstream? /- increases, so the NPSH of the circulation pump also increases by about 2
Decreased by 0m.

When the reactor pressure is high during steady operation of the reactor, the suction pressure of the circulation pump is also sufficiently high, so a drop of about 20 m is not a problem. However, the reactor pressure is about 10Kg/ffl
If the temperature is below, there is a possibility that cavitation will occur.

In particular, when the reactor is shut down, the reactor pressure drops to atmospheric pressure, and the circulation pump NP8H drops to nearly 2 m as shown in FIG. In FIG. 7, the reactor pressure PI is atmospheric pressure IQ, 5 m, the hydrostatic head Δh is approximately 30 m, the pressure loss ΔP is approximately 37 m, and the saturated steam pressure PI+ at the circulation pump inlet is 1.
This is because when sm(atsOc) is assumed and NPSH is calculated, NPSH=P++Δh−ΔP−Ps=2m. On the other hand, the NPSH required by the structural elements of the circulation pump is several meters or more, and if this cannot be ensured, cavities will occur. One possible way to prevent this is to lower the level by approximately 10 m when installing a circulation pump. However, even at present, in order to increase the circulation pump NPSH, most plants are installed on the floor above the mat floor, which is the lowest level, and even if the circulation pump is lowered to the mat floor, it is only a few meters at most. However, the level of installation cannot be lowered. Further, due to the structure of the pump, it is impossible to reduce the required NPSH to about 2 m.

Based on the above studies, in the reactor coolant purification system of the present invention, regeneration is performed from the pump discharge piping of the residual heat removal system, which is one of the coolant circulation systems that was originally provided in the reactor for purposes other than coolant purification. A bypass pipe is installed that connects to the heat exchanger inlet pipe, and when the reactor is stopped or the pressure is low, the residual heat removal pump increases the pressure of the coolant and sends it to the reactor coolant purification system, and the NPSH of the circulation pump is activated. This is to ensure that there is sufficient capacity.

[Embodiment of the Invention] Hereinafter, one embodiment of the reactor coolant purification device of the present invention will be described as a first embodiment.
A recirculation pump 2 is connected to a reactor pressure vessel 1 through piping to form a closed loop recirculation device. The basic loop of the coolant purification device branches off from the suction pipe of the recirculation pump 2 and connects to the regenerative heat exchanger 4. It is a route that passes through the non-regenerative heat exchanger 5, the circulation pump 6, the filtration desalination device 7, the shell side of the regenerative heat exchanger 4, and then returns to the reactor pressure vessel 1 via the water supply pipe 8. Further, the residual heat removal pump 10.branches from the suction pipe of the recirculation pump 2. The loop through the residual heat removal heat exchanger 11 and back again to the recirculation pump discharge piping is the residual heat removal system. The purpose of this system is to cool the reactor using the residual heat removal heat exchanger 11 when the reactor is shut down or when the pressure is low.

In particular, in the present invention, a bypass pipe 13 is provided which connects the discharge pipe of the residual heat removal pump IO to the regenerative heat exchanger inlet pipe 3, and a valve 14 is installed in this pipe 13, and a bypass of the regenerative heat exchanger inlet pipe 3 is provided. A valve 15 is installed upstream of the connection point of the pipe 13 to enable flow path switching. Note that if the branch point of the bypass pipe 13 is not the outlet of the residual heat removal pump 10 but the outlet of the residual heat removal heat exchanger 11 as shown by the dotted line, the coolant after cooling can be sent to the reactor coolant purification system. It is even more effective because it can be transported.

The non-regenerative heat exchanger 5 and the residual heat removal heat exchanger 11 each have auxiliary cooling water passed through pipes 9 and 12 to the shell side, and heat exchange cooling of the high-temperature coolant flowing on the pipe side. .

Next, the operation in this configuration will be explained. First, when the reactor is shut down and at low pressure (approximately 9/- or less), the residual heat removal system performs the reactor cooling operation as its original system function, so there is no coolant in the loop of this system. It's circulating. At this time, the valve 15 is closed, the valve 14 is opened, a portion of the coolant is drawn out from the residual heat removal pump discharge pipe through the bypass pipe 13, and the coolant is transferred to the regenerative heat exchanger 4. Non-regenerative heat exchanger 5° circulation pump 6, filtration desalination device 7. It is returned to the reactor pressure vessel 1 via the route on the side of the regenerative heat exchanger 4 shell.

Since the discharge pressure of the residual heat removal pump 10 is applied to the suction side of the circulation pump 6, NPSH is ensured and there is no fear of cavitation occurring. The reactor pressure rose to about 10
When the temperature exceeds Kp/m, the valve 14 is closed and the valve 15 is opened, as shown in the valve opening/closing state in FIG. In this state, similar to the conventional reactor coolant purification system, part of the coolant is drawn out from the recirculation pump 2 through the suction pipe 3 and guided to the reactor coolant purification system. Since the reactor pressure is sufficiently high, sufficient NPSH of the circulation pump is ensured, and there is no possibility of cavitation occurring.

As described above, according to the reactor coolant purification system of the present invention, the NP of the circulation pump 6 is
Since sufficient SH is ensured, there is no need to worry about cavitation. Moreover, since the circulation pump 6 is always operated at a low temperature (approximately 50 C), as shown in FIG. The surface dose rate of the pump is about 1/10 of that of the pump, which significantly reduces radiation exposure for workers during maintenance and inspection. Further, the capacity of the residual heat removal pump 10 is determined in the core cooling mode at the time of a nuclear reactor accident, and a smaller capacity is sufficient for cooling operation at the time of reactor shutdown. Therefore, at present, when the nuclear reactor is shut down, a portion of the remaining flow rate is bypassed through the residual heat exchanger 11. The present invention also has the effect of effectively utilizing the surplus flow rate of the residual heat removal system by passing it through the reactor coolant purification system.

Another embodiment of the reactor coolant purification system of the present invention will be described with reference to FIG. Compared to the embodiment shown in FIG. 1, this embodiment has a configuration in which the circulation pump 6 is installed further downstream of the filtration and demineralization device 7 on the downstream side. If the circulation pump 6 is placed downstream of the filtration and demineralization device 7, the pressure loss of the filtration and demineralization device 7 will increase by a maximum of approximately 4 K9/cfI, but even when the reactor is shut down or at low pressure, Since the discharge pressure of the residual heat removal pump 10 is applied, a sufficient NPSH of the circulation pop 6 is ensured, and there is no fear of cavity shore occurring. According to this embodiment, the removal rate of radioactive corrosion products in the coolant by the filtration salt theory device 7 is approximately 1/10.
0, the surface dose rate of the circulation pump 6 is approximately 1/1000 (= 1/100XI/10
) is significantly reduced.

〔Effect of the invention〕

According to the present invention, since the circulation pump can be installed on the low temperature side of the coolant, it is possible to significantly reduce the amount of radioactive products attached to the circulation pump. This has a significant effect on reducing radiation exposure. Moreover, there is an effect of ensuring sufficient NPSH of the circulation pump over the entire operating range of the nuclear reactor.

[Brief explanation of the drawing]

Figures 1 and 2 are system diagrams of an embodiment of the reactor coolant purification system of the present invention, Figures 3 and 4 are system diagrams of a conventional reactor coolant purification system, and Figure 5 is a system diagram of an embodiment of the reactor coolant purification system of the present invention. A system diagram of the proposed reactor coolant purification system, Fig. 6 is a characteristic diagram showing the relationship between coolant temperature and surface dose rate, and Fig. 7 is a schematic calculation diagram of the circulation pump NFSH. 1...Reactor pressure vessel, 2...Recirculation pump, 3.
... Regenerative heat exchanger inlet piping, 4... Regenerative heat exchanger, 5
...Non-regenerative heat exchanger, 6...Circulation pump, 7...
Filtration desalination equipment, 8... Water supply pipe, 9, 12. 19...
Piping, 1o... Residual heat removal pump, 11... Residual heat removal heat exchanger, 13... Bypass piping, 14, 15,
20.21... Valve, 16... Mixed bed desalination equipment, 17
...Pressure reducing valve, 18...Auxiliary pump.

Claims (1)

[Scope of Claims] 1. A reactor coolant purification device that takes a part of the coolant from the reactor, cools it in a heat exchanger, increases the pressure with a pump, purifies it with a filtration desalination device, and returns it to the reactor, Bypass piping is provided from downstream of the residual heat removal pump of the residual heat removal system that circulates coolant even when the reactor is stopped or at low pressure, and upstream of the heat exchanger, so that when the pushing pressure of the purification system pump is insufficient, residual heat removal A nuclear reactor coolant purification system characterized by pressurization using the pressure of a heat removal pump. 2. A reactor coolant purification device according to claim 1, wherein the purification system pump is installed downstream of a filtration desalination device. 3. In claim 1 or 2, the bypass pipe is connected downstream of a residual heat removal heat exchanger disposed downstream of the residual heat removal pump, and is pressurized therefrom. Reactor coolant purification equipment.