JPH0314154B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a coolant supply system for a nuclear reactor, and in particular, the present invention relates to a coolant supply system for a nuclear reactor. The present invention relates to a structure of a coolant supply system for a nuclear reactor that is suitable for reducing energy consumption.

[Prior Art] Steam generated in the pressure vessel of a boiling water nuclear reactor is sent to a turbine and condensed in a condenser. The cooling water obtained by condensation passes through a demineralizer, is heated to a predetermined temperature by a plurality of feed water heaters, and is then returned to the reactor pressure vessel.

Activated crud and ions brought into the reactor pressure vessel with cooling water are removed by a desalter. Additionally, oxygen is injected into the coolant supply system on the outlet side of the demineralizer to prevent crud formation due to corrosion of the coolant supply system. By taking such measures, the amount of material brought into the reactor pressure vessel and activated will be significantly reduced.

However, the surface dose rate of the recirculation system piping connected to the reactor pressure vessel showed a gradual trend over the years.

[Problem to be solved by the invention] Therefore, for example, "Toshiba Review" (Vol. 35, No. 5)
As stated on pages 404-409 (issued April 1982), it was proposed to reduce the cobalt content of all feedwater heater tube materials based on the reality that cobalt plays a major role as a radiation source. Therefore, the objective of reducing the amount of cobalt brought in was achieved to some extent.

By the way, feed water heaters in 1100 MWe class boiling water reactors use tube materials of approx.
300 tons of stainless steel material is used. Conventional stainless steel materials that do not particularly limit the cobalt content cost around 3,500 yen/Kg, while stainless steel materials with reduced cobalt cost 20% to 20%, although this varies depending on the specifications.
It will be about 70% higher.

Therefore, as proposed in the above literature, if the tube materials of all feed water heaters are made to have low cobalt content, the cost will be 3,500 yen x (20-70)% x 300 tons = 210 million yen to 735,000 yen. This will increase costs by as much as 10,000 yen. As described above, there was a problem in which the cost increased by at least 210 million yen, depending on the extent to which cobalt was restricted.

The purpose of the present invention is to reduce the amount of cobalt carried into the reactor pressure vessel by reducing the amount of cobalt contained in all feedwater heater tubes, and to reduce the cost increase as much as possible. The objective is to provide a coolant supply water system.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a pipe for supplying coolant into a reactor vessel, a plurality of shell-and-tube type heaters installed in the pipe, and a pipe for supplying a coolant into a reactor vessel. In a nuclear reactor coolant supply system consisting of
℃ or higher, the tube of the heater is made of stainless steel with a cobalt content of 0.25% or less or titanium material with a cobalt content of 0.1% or less, and the coolant temperature in the pipe is below 100℃. The heater tube located in the reactor provides a coolant supply system for the nuclear reactor made of stainless steel with a higher cobalt content than the stainless steel mentioned above.

[Function] The present invention was made based on unique findings obtained through detailed study of the impurity concentration contained in the coolant in each part of the coolant supply system of a boiling water reactor. . The examination process will be explained next.

Analysis of impurities in the cooling water just before it flows into the reactor pressure vessel from the downstream side of the desalter revealed that it contained a large amount of cobalt (Cobalt 59). This cobalt has not yet been activated. 100% cobalt concentration just before entering the reactor pressure vessel
FIG. 1 shows an example of the relative concentration distribution of cobalt in each part of the coolant supply system. The cooling water in the coolant supply system is heated by the feed water heater,
As its temperature rises, the amount of cobalt in the cooling water increases. When the cooling water temperature reaches 100°C or higher, the amount of cobalt in the cooling water starts to increase, and especially when the cooling water temperature reaches 150°C or higher, the amount increases significantly. The reason for this increase is thought to be that when the cooling water temperature reaches 100°C or higher, cobalt is eluted from the piping of the coolant supply system that comes into contact with the cooling water.

Non-radioactive cobalt, such as cobalt-59,
When it flows into the reactor pressure vessel, it is irradiated with neutrons and turns into cobalt-60, which is radioactive cobalt. For this reason, cobalt 60 is added to the inner surface of the recirculation system piping.
is accumulated, increasing the surface dose rate on the inner surface of the recirculation system piping.

Ultimately, the reason why the surface dose rate of recirculation system piping and the like increases is that cobalt is leached into the coolant from the coolant supply system. Therefore, if this elution of cobalt is prevented, an increase in the surface dose rate of recirculation system piping, etc. can be suppressed.

Generally, the pipes of the coolant supply system are made of carbon steel, and the heat exchanger tubes of the feed water heater are made of SUS304. For example, six feed water heaters are installed in the coolant supply system. A, B shown in Figure 1,
C, D, E, F indicate the 1st stage, 2nd stage, 3rd stage, 4th stage, 5th stage, and 6th stage (final stage) feed water heaters installed in the coolant supply system. ing. In this way, we investigated the source of cobalt elution in the coolant supply system, including the feedwater heater made of SUS304 structural material, and found that the heat exchanger tube of the feedwater heater, which is located where the cooling water temperature is over 100℃, It turns out that there is something. In other words, cobalt contained in SUS304 is eluted into the cooling water.

Therefore, if only the feed water heater that elutes a large amount of cobalt is replaced with a feed water heater that has heat transfer tubes made of a low cobalt-containing material, it will be the same as replacing the heat transfer tubes of the entire feed water heater with low cobalt-containing materials. Equally,
It becomes possible to reduce the amount of cobalt brought into the reactor pressure vessel and to suppress cost increases as much as possible.

Practically speaking, if only the heat transfer tubes in the feed water heater where the temperature exceeds 150°C are replaced with low cobalt-containing materials,
Although the cost reduction effect is significant, in order to increase the safety factor, the heat exchanger tubes in the feedwater heaters where the temperature reaches 100°C or higher will be replaced with low-cobalt-containing materials.
Even in that case, costs can be significantly reduced compared to replacing the heat exchanger tubes in the entire feedwater heater with low-cobalt-containing materials.

[Embodiment] FIG. 2 shows a system configuration of a preferred embodiment of the present invention based on the results of such studies.

Steam generated in the reactor pressure vessel 1 passes through the main steam pipe 2 and is sent to the turbine 3. Steam discharged from the turbine 3 is condensed in a condenser 4. The condensed water in the condenser 4 is pressurized by the condensate pump 5 and sent to the demineralizer 6 as cooling water. Desalter 6
removes cruds and ions contained in the cooling water. The cooling water flowing out from the demineralizer 6 is sequentially heated while passing through the feed water heaters 7, 8, 9, 10, 11, and 13, and its pressure is increased by the feed water pump 12.
The water passes through the water supply pipe 19 and is returned into the reactor pressure vessel 1 . Recirculation system piping 14 is installed in the reactor pressure vessel 1.
A recirculation system is provided including a recirculation pump 15 and a recirculation pump 15 . A furnace purification system piping 17 branches off from the recirculation system piping 14, and is configured to return purified reactor water to the water supply piping 19 via a furnace purification system pump 16 and a purification device 18.

Each feed water heater 7, 8, 9, 10, 11, 1
3 is a shell and tube type heat exchanger, and has a structure in which cooling water flows inside the tube, that is, inside the heat transfer tube, and steam extracted from the turbine flows through the shell side. That is, the feed water heater heats cooling water with steam extracted from the turbine.

In this embodiment, the heat transfer tubes of the feed water heaters 11 and 13, which are disposed in the portion of the water supply piping 19 where the cooling water temperature is 150° C. or higher, are made of a low cobalt-containing material.

When the heat exchanger tubes of feed water heaters 11 and 13 are made of SUS304 with low cobalt content (0.25% or less),
The amount of cobalt eluted into the cooling water is as indicated by the broken line 20 in FIG.

As described above, in this embodiment, the amount of cobalt flowing into the reactor pressure vessel 1 is drastically reduced to about 1/10 of the conventional amount. Therefore, the surface dose rate of the recirculation system piping 14 and the like decreases to 1/10. Therefore, the time required for maintenance and inspection of the recirculation system piping 14, the furnace purification system piping 17, etc. can be significantly shortened.

In this example, among the six stages of feed water heaters,
Only the heat exchanger tubes of the last two stages of feed water heaters E and F are manufactured from stainless steel with low cobalt content.
Compared to the case where there is no limit on cobalt content, 3500 yen x (20 to 70)% x 100 tons = 70 million yen to 200 million yen
The cost increase will be limited to around 45 million yen.

Therefore, a cost reduction of 140 million yen to 490 million yen will be achieved compared to the case where the entire heat exchanger tube of the 6-stage feed water heater is made of low cobalt-containing stainless steel.

Instead of the low cobalt-containing stainless steel of the above embodiment, the heat exchanger tube of the feed water heater may be manufactured from a low-cobalt titanium material. The cobalt content of titanium materials is generally 0.1% or less.

When the heat exchanger tubes of the feed water heaters 11 and 13 are manufactured from a titanium material containing low cobalt, the amount of cobalt eluted is further reduced to 1/10 compared to when they are manufactured from SUS304 containing low cobalt.

When the heat transfer tubes of the feedwater heater are manufactured from titanium material containing low cobalt in this way, the amount of cobalt eluted into the cooling water flowing inside the feedwater piping is significantly reduced, and non-radioactive cobalt flowing into the reactor pressure vessel 1 is reduced. The quantity becomes even smaller.

In the above example, only the heat transfer tubes of the feed water heaters 11 and 13, which are arranged in the portion of the water supply pipe 19 where the cooling water temperature is 150°C or higher, were manufactured from a low cobalt-containing material, but it is possible to further reduce the amount of eluted cobalt. The heat exchanger tubes of the feed water heaters 9, 10, 11, and 13, which are placed in locations where the cooling water temperature is 100°C or higher, are also made of SUS304 with a low cobalt content (0.25% or less).
Alternatively, it may be manufactured from a titanium material containing low cobalt.

In this case, of the six stages of feed water heaters, only the heat exchanger tubes of the last four stages of feed water heaters C, D, E, and F are manufactured from stainless steel with low cobalt content, so there is no limit to the cobalt content. Compared to the case without installation, 3,500 yen x (20-70)% x 200 tons = 140 million yen ~
The cost will increase by approximately 490 million yen. In this case as well, 6
Compared to the case where the entire heat exchanger tube of the stage feedwater heater was made of low-cobalt stainless steel, a cost reduction of 70 million yen to 245 million yen will be achieved.

[Effects of the Invention] According to the present invention, only the heat exchanger tubes of the feed water heater disposed in the portion of the water supply piping that reaches a temperature of 150°C or higher (more precisely, 100°C or higher) are made low in cobalt. Therefore, it is possible to reduce the amount of cobalt carried into the reactor pressure vessel by reducing the amount of cobalt carried into the reactor pressure vessel, equivalent to reducing the cobalt content of heat exchanger tubes in all feedwater heaters, while at the same time minimizing cost increases. A coolant water supply system is obtained.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing the relationship between the position of the feedwater heater and the relative concentration of cobalt in the cooling water with respect to the temperature of the cooling water in the coolant supply system, and Fig. 2 is an implementation of the coolant supply system for a nuclear reactor according to the present invention. FIG. 2 is a system diagram showing an example configuration. 1...Reactor pressure vessel, 2...Main steam pipe, 3...
...Turbine, 4...Condenser, 5...Condensate pump,
6... Desalter, 7, 8, 9, 10, 11, 13...
...Feed water heater, 12...Water pump, 14...Recirculation system piping, 15...Recirculation pump, 16...Furnace purification system pump, 17...Furnace purification system piping, 18...
Purification equipment, 19...Water supply piping.

Claims (1)

[Scope of Claims] 1. A reactor coolant supply system comprising a pipe for supplying coolant into a reactor vessel and a plurality of shell-and-tube type heaters installed in the pipe, comprising: Among the heaters, the tube of the heater located in the part of the pipe where the coolant temperature is 100°C or higher is made of stainless steel with a cobalt content of 0.25% or less or titanium material with a cobalt content of 0.1% or less. , the coolant temperature in the pipe is 100℃
A coolant supply system for a nuclear reactor, characterized in that a tube of a heater disposed in a portion where the cobalt content is lower than that of the stainless steel is made of stainless steel having a higher cobalt content than the stainless steel.