JPS5928279B2 - Main condenser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a main condenser for a boiling water nuclear power generation facility.

Boiling water nuclear power generation uses high-temperature steam generated in a nuclear reactor to rotate a turbine and generate electricity, but the steam used to generate electricity is converted back to water by a main condenser and sent back into the reactor.

Non-condensable gases that are not condensed in the main condenser are deradiated and released into the atmosphere as so-called gaseous waste.

Figure 1 shows the configuration of the main condenser. Steam generated in the reactor 1 passes through a high-pressure turbine 2 and a low-pressure turbine 3, and then is sent to the main condenser 4, where it is condensed. The water is returned to the reactor 1 again.

Gas that is not condensed in the main condenser 4 is extracted by an air extractor 5, and after being preheated by an exhaust gas preheater 6, hydrogen and oxygen become water in an exhaust gas combiner 7, and are removed in an exhaust gas condenser 8. It will be destroyed.

Other exhaust gases are deradiated by the hold up pipe 9 and rare gas hold up device 10, and are deradiated by the exhaust pipe 1.
1 is released into the atmosphere.

FIG. 2 shows the structure of the main condenser. Inside the main condenser 4, there is a steam chamber 13 in which a large number of cooling pipes 12 are arranged.
is provided, and the steam introduced from the upper part of the main condenser 4 is
It passes between the cooling pipes 12 and is cooled by the seawater flowing inside the cooling pipes 12, and most of it becomes condensed water.

The condensed water falls onto the roof 15 of the hot well 14 located at the bottom of the main condenser 4.

Since the roof 15 is sloped, the condensed water flows down and flows into the water channel from both ends of the hot well 14.

On the other hand, steam and non-condensable gas that did not condense while passing between the cooling pipes 12 of the main condenser 4 pass through the gas phase section 16 provided in the center of the main condenser 4. , are led to the outside of the main condenser 4 from the gas exhaust pipe 17.

As is clear from such a structure of the main condenser, conventionally, non-condensable gas was guided to the gaseous waste treatment system without remaining in the main condenser.

Therefore, the radioactive gas flowing into the main condenser together with the steam generated in the nuclear reactor is transferred to the gaseous waste treatment system with almost no attenuation of its radioactivity.

The radioactive gases generated in nuclear reactors include fission products such as krypton or xenon that leak when fuel rods inside the reactor break, and nitrogen (N)-16 that is generated due to radiolysis of reactor water. There is a radioactive gas consisting of:

The former type of fission products poses almost no problem unless the fuel rods are damaged, and even if radioactive gas is generated due to fuel rod damage, there is almost no problem with radiation leakage in the gaseous waste treatment system. .

On the other hand, activated gas is generated regardless of fuel damage and flows into the main condenser together with the main steam, and N-16 in this activated gas has extremely high energy (
6 to 7 MeV), it is almost impossible for people to enter the air extractor 5, exhaust gas preheater 6, etc. while the power plant is in operation. This influence is also large on the water dispenser 8.

That is, for example, the dose rate on the surface of the air extractor 5 of a power plant with an electric output of 1 million kW class is about 5 rer11/hr degree, and the dose rate on the surfaces of the exhaust gas preheater 6 and the exhaust gas combiner 7 is about 0. .3 rem/hr to 1 rem/
It is hr.

For this reason, in conventional nuclear power plants, equipment such as the air extractor 5, exhaust gas preheater 6, exhaust gas combiner 7, etc. is installed inside a shielding wall, which increases the dose rate in the passage near the shielding wall. We are trying to reduce the

For this reason, a shielding wall with a capacity of 100 (1'771 to 150 cIrL) has been constructed, and the shielding wall has an entrance and exit structure that takes into consideration the shielding for entering in the event of a malfunction of these devices, but the dose rate on the surface of these devices Because of the extremely high amount of electricity, it was virtually impossible to carry out maintenance work on these devices while the power plant was in operation.

For example, while the power plant is operating, you can only get close to the air extractor 5 for about one minute, so if repairs are unavoidable, the power plant must be stopped to carry out the work. There wasn't.

Therefore, in a conventional boiling water nuclear power plant, the thickness of the shielding wall around the air extractor, exhaust gas preheater, etc. is very thick, and as a result, the space occupied by the shielding wall in the power plant is large, and the power plant The building itself becomes larger and the cost increases.

The dose rate is high around the air extractor, exhaust gas preheater, etc.
It is impossible to maintain or repair the power plant while it is operating.

If any of these devices were to fail, the operation of the entire power plant would have to be shut down, resulting in lower operating rates and higher costs for commercial furnaces.

The present invention aims to reduce the equipment surface dose rate in the waste treatment system following the main condenser of boiling water nuclear power generation equipment. an exhaust port for discharging the non-condensable gas that has passed through the chamber to an external gaseous waste treatment system, a series of condensate passages, and an upper part of the condensate passages that is partitioned from the steam chamber. In a main condenser having a hot well having a space, the non-condensable gas is introduced into the space from one end, and is led out to the exhaust port from the other end via the space and radiated. It is characterized by having a flow path that attenuates the power.

Examples will be described below with reference to the drawings.

FIG. 3 shows the structure of one embodiment, and the same numbers as those in FIG. 2 indicate the same parts.

The difference between this device and the conventional main condenser shown in Figure 2 is that
The gas phase part 16 is not directly connected to the gas discharge pipe 17, and the gas phase part 16 is connected to the space 19 above the water surface of the water channel of the hot well 14 through the non-condensable gas pipe 18. Gas discharge pipe 1 is connected to the pipe 21 that connects to the roof 15 of the hot well 14 located at the upper part of the final stage water channel 20.
This is the point where it is connected to 1.

As shown in the vertical cross-sectional view of FIG. 3 and the cross-sectional view of FIG. 4, the hot well 14 is provided at the bottom of the main condenser 4 and has a tapered roof 15. Between the bottom and the roof 15, there is a partition wall 22 held at a constant interval whose upper and lower sides are fixed to the roof 15 and the bottom of the main condenser, respectively.
The side walls of this bulkhead 22 are alternately fixed to the opposing side walls of the main condenser, and an initial water channel 23 for condensed water is formed at both ends of the hot well, and a condensed water channel 23 is formed at the bottom of the center part. A condensate outlet 24 is provided, and the condensed water that enters the hot well 15 from the first stage waterway 23 passes through the meandering flow path formed by the partition wall 22 of the hot well 14 and exits the condensate system from the condensate outlet 24. I'm going to go.

In addition, the non-condensable gas that has entered the hot well 14 through the non-condensable gas pipe 18 passes through the meandering space on the meandering condensed water flow path formed by the partition wall 22, passes through the pipe 21, and returns from the main gas discharge pipe 17. Configured to exit the water bowl.

Therefore, the steam entering from the upper part of the main condenser 4 and the N-1
While the non-condensable gas such as 6 passes between the cooling pipes 12, the steam is condensed and collected in the first stage waterway 23 of the main condenser 4, and is sequentially passed through the meandering flow path in the hot well 14. transition,
On the other hand, non-condensable gas exits the condensate system from the condensate outlet 24 and is guided from the gas phase section 16 through the non-condensable gas piping 18 to the first-stage water channel 23 side on both sides of the main condenser 4. , passes through the hot well 14 through the space 19 above the water surface of the water channel through the same meandering flow path as the condensed water, passes through the top of the hot well 14, exits the gas discharge pipe 17 to the outside of the main condenser 4, and the air is It is guided to the extractor 5.

In this way, when the non-condensable gas is passed through the hollow space 19 above the condensate water channel of the hot well 14, the non-condensable gas flows into the main condensate water for about 20 seconds compared to the conventional case as shown in FIG. Vessel 4
It is possible to keep it inside.

Generally, radioactivity decays exponentially over time, but Figure 5 shows the relationship between the hold-up time (sec) and the decay rate of the N-16 condenser. -16 indicates that there is a large difference in radioactivity intensity due to a slight difference in residence time, and considering that its half-life is approximately 7 seconds, it is assumed that the main condenser 4 By increasing the residence time in the condenser by approximately 20 seconds, the radioactivity intensity of N-16 immediately after leaving the main condenser 4 is 1/10 that of the conventional case. The surface dose rate of extractors etc. will also be 1/10.

If the dose rate on the equipment surface is reduced to 1/10 in this way, it will be possible to approach equipment such as air extractors even while the power plant is operating, and it will be possible to conduct patrols and maintenance work. It is now possible to reduce the thickness by more than 20 CrrL than before, making it possible to effectively utilize space within the building, and reducing the amount of concrete to 1.50 m.
3 (approximately 340 tons), and construction costs can be reduced.

Even if equipment breaks down, simple repairs can be made without stopping the power plant, which has the effect of improving the operating rate of the power plant.

As described above, the present invention makes it possible to reduce the equipment surface dose rate in the waste treatment system following the main condenser of boiling water nuclear power generation equipment, and also makes it possible to reduce exposure at nuclear power plants. This has great industrial effects.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of the waste treatment system following the main condenser of a nuclear power generation facility, Fig. 2 is a vertical cross-sectional view of a conventional main condenser, and Fig. 3 is an illustration of the main condenser of the present invention. FIG. 4 is a longitudinal cross-sectional view of the embodiment, and FIG. 4 is a cross-sectional view of the main part thereof. FIG. 5 is a characteristic curve diagram showing the relationship between the hold-up time and the attenuation rate of the condenser. Explanation of symbols, 4...Main condenser, 12...
・Cooling pipe, 13...Steam room, 14...
Hot well, 16... Gas phase section, 17...
...Gas discharge piping, 18...Non-condensable gas piping.

Claims (1)

[Claims] 1. A gas phase section provided in the steam chamber, an outlet for discharging non-condensable gas that has passed through the gas phase section to a gaseous waste treatment system provided outside, and a series of A main condenser having a condensate passage and a hot well having a space formed above the condensate passage to be partitioned from the steam chamber, the non-condensable gas is supplied from one end to the space. What is claimed is: 1. A main condenser comprising a flow path for introducing radioactivity into the air and leading it out from the other end to the exhaust port via the space to attenuate radioactivity. 2. The space of the hot well is formed by a plurality of partition walls and has a medium-high top meandering from the outer peripheral end toward the center, one end of which is located at the outer peripheral end, and the other end of which is located at the outer peripheral end. The main return channel according to claim 1, which is located at the top.