JPH0750193B2 - Cleaning device for spent fuel assemblies - Google Patents

Description

Detailed Description of the Invention TECHNICAL FIELD OF THE INVENTION

The present invention relates to a spent fuel assembly cleaning device for a spent fuel assembly of a fast breeder reactor using liquid metal such as sodium as a primary coolant.

[Prior art and its problems]

As is well known, the spent fuel assemblies taken out from the reactor described above are generally washed with liquid metal such as sodium adhering to the fuel assemblies in the process of the previous stage of storing in the fuel storage pool. Has been done. As a method of cleaning the spent fuel assembly in this case, conventionally, after the spent fuel assembly is accommodated in the cleaning tank, a wet gas containing steam is sprayed onto the spent fuel assembly, and after cleaning with water, A steam-water washing method is known in which a fuel assembly is dried with warm air or the like. However, such a steam-water cleaning method requires a long time of 1.5 hours for cleaning one spent fuel assembly, and the cleaning also requires about 1.5 tons per spent fuel assembly. Since a large amount of radioactive cleaning waste liquid containing radioactive clad and radioactive corrosion products, etc., is generated, there is a problem in waste disposal such as enlargement of waste liquid treatment system equipment and increase of radioactive contamination. . On the other hand, as a cleaning method that eliminates the above-mentioned drawbacks of the conventional steam-water cleaning method and eliminates liquid metal adhering to the spent fuel assembly without generating radioactive waste liquid, first, the spent fuel assembly is used. Is preheated to a temperature equal to or higher than the melting temperature of the liquid metal such as sodium, and the atmosphere in the cleaning tank is stored in the cleaning tank after the preheated spent fuel assembly is stored in the cleaning tank. A dry reduced pressure cleaning method has been proposed in which the liquid metal adhering to the fuel assembly is evaporated and eliminated by reducing the pressure to a saturated vapor pressure or lower. According to such a dry vacuum cleaning method, since no steam, water, etc. are used in the cleaning process, there is no generation of radioactive waste liquid due to cleaning, and a relatively small amount of exhaust gas is simply treated in the gaseous waste treatment system to spend spent fuel assembly. It becomes possible to wash the body effectively. Next, the outline of the dry vacuum cleaning method for the spent fuel assembly of the fast breeder reactor using sodium as the primary coolant will be outlined with reference to FIG. In the figure, 1 is a cleaning tank equipped with a door valve 2 on the top, and 3 is a spent fuel assembly housed in the cleaning tank, where a blower 4, a gas heater 5, and a gas cooling are provided for the cleaning tank 1. An inert gas circulation line 8 equipped with a vessel 6, a vapor trap 7 and the like and connected and connected to the cleaning tank 1, and an inert gas source 9 of, for example, argon gas connected to the inert gas circulation line 8. It is equipped with a preheating means for the spent fuel assembly, including a decompression means, which is a decompression exhaust line 14 leading from the cleaning tank 1 through the vacuum tank 10, the vacuum pump 11, the vapor trap 12 and the like to the gaseous waste treatment system 13. There is. Cleaning tank 1 and vacuum tank
10 is drawn from the bottom of the sodium drainage tank 15, the sodium feed pump 16 and the sodium recovery system 1
A sodium drain line 18 leading to 7 is connected and connected. Reference numerals 19 to 29 are open / close valves inserted in the system of the gas circulation line, the reduced pressure exhaust line, and the drain line. Next, the procedure of the cleaning operation of the spent fuel assembly with the above configuration will be described. First, the spent fuel assembly 3 taken out of the nuclear reactor is housed in the cleaning tank 1 through the door valve 2. Here, the valves 19 to 21 are opened, a predetermined amount of argon gas is introduced into the system from the inert gas source 9, and the blower 4,
When the gas heater 5 is started, the heated gas is circulated and sent into the cleaning tank 1 to generate decay heat, and a full length region of the spent fuel assembly 3 including a non-heat generating portion other than the fuel pin. The temperature is increased by heating to a predetermined preheating temperature (preferably about 450 to 550 ° C.) that is equal to or higher than the melting temperature of sodium. In addition, when the temperature of the spent fuel assembly 3, especially the surface temperature of the fuel pin that generates decay heat, reaches the allowable temperature in the process of this preheating step, the inert gas circulation line 8 is temporarily cooled. The gas cooler 6 is started to lower the circulating gas temperature, and the temperature is adjusted so that the spent fuel assembly 3 is maintained at a predetermined preheating temperature. On the other hand, during the preheating process, the vacuum pump 11 is started with the valves 22 and 23 closed and the vacuum tank 10 is depressurized. Here, the blower 4 and the gas heater 5 are stopped and the valves 19 and 20 are closed when the spent fuel assembly 3 reaches a predetermined preheating temperature by the preheating process described above, and then the vacuum tank 10 is first connected to. The valve 22 is opened to rapidly reduce the pressure inside the cleaning tank 1. Then close the valve 22 and close the vacuum tank.
After disconnecting between 10 and 10, the valve 23 is opened and the inside of the cleaning tank 1 is further evacuated by the vacuum pump 11, and the internal pressure in the cleaning tank is equal to or lower than the saturated sodium vapor pressure for that temperature, for example, about 4 to 10 Torr. Evacuate under reduced pressure. As a result, the sodium adhering to the surface and inside of the spent fuel assembly 3 is promoted to be evaporated, and is removed by washing from the spent fuel assembly 3 in the form of sodium vapor and mist. Most of the sodium vapor and mist generated in this process are transferred to the inside of the cleaning tank 1 and the vacuum tank 10 and adhered thereto, and the remaining suspended vapor and mist are accompanied by the exhaust gas, and the vapor trap in the decompression exhaust line 14 is included. Only the amount of exhaust gas adsorbed and removed by 12 and commensurate with the internal volume of the cleaning tank 1 is sent to the gas waste processing system 13 for processing. The above washing operation is repeated several times if necessary,
The spent fuel assembly 3 is thoroughly washed and a series of washing steps is completed. Along with the above cleaning, cleaning tank 1, vacuum tank
The sodium vapor-deposited on 10 was heated by the heating heater (not shown) equipped in the cleaning tank and the vacuum tank, and the decay heat of the spent fuel assembly itself to melt the sodium, and then the valves 26 and 27 were opened. Then, the sodium is discharged to the drain tank 15, and from there, it is sent to the sodium recovery system 17 by the sodium feed pump 16 and recovered. By the way, in the dry vacuum cleaning method described above, a large amount of cleaning waste liquid is not generated unlike the steam-water cleaning method,
Even so, since a relatively small amount of waste gas is generated with the decompression operation of the cleaning tank each time cleaning is performed, it is unavoidable to treat this waste gas in the gaseous waste treatment system, and this consumption At the next cleaning, the amount of gas needs to be newly supplied from the inert gas source to the inert gas circulation line, which increases the cleaning operation cost.

[Object of the Invention]

The present invention has been made in view of the above points, and improved the dry type vacuum cleaning device described above, without exhaust gas generated in the depressurizing step at the time of cleaning, to be treated again in the preheating step in the next cleaning. Utilizing the amount of gas waste generated,
Another object of the present invention is to provide a cleaning device for a spent fuel assembly, which has a low operating cost and is highly economical, which is capable of significantly reducing the amount of new inert gas supply.

[Points of the Invention]

In order to achieve the above object, the present invention is a dry type vacuum cleaning apparatus described above, connecting the exhaust gas return line connecting between the vacuum exhaust line and the inert gas circulation line, the exhaust gas return line, It comprises a gas storage tank for temporarily storing the exhaust gas from the reduced pressure exhaust gas line and a blower for supplying the stored gas in the gas storage tank to the inert gas circulation line, and exhausts it from the cleaning tank in the depressurization step during cleaning. The generated exhaust gas is supplied to the inert gas circulation line through the exhaust gas return line and used in the preheating process of the spent fuel assembly at the next cleaning, thereby generating the amount of gaseous waste and newly supplying the inert gas source. The amount of gas replenished from is remarkably reduced.

Examples of the invention

FIG. 1 shows a system diagram of a cleaning equipment according to an embodiment of the present invention, and parts corresponding to those in FIG. 2 are designated by the same reference numerals. Here, according to the present invention, an exhaust gas return line 35 equipped with a gas storage tank 30, a blower 31, and opening / closing valves 32 to 34 is connected between the downstream side point of the vacuum pump 11 in the decompression exhaust line 14 and the inert gas circulation line 8. Is connected to the pipe. Next, the procedure of the cleaning operation with the above-described configuration will be described. First, the spent fuel assembly 3 as the object to be cleaned is cleaned with the cleaning tank 1.
Preheating process of spent fuel assembly, which is carried out in the
The depressurization process proceeds in the same manner as in FIG. Wash tank 1 here
When decompressing the inside of the chamber, the exhaust gas treatment system 13 is usually used.
Close the valve 25 leading to the exhaust gas return line
The valve 32 on the inlet side of 35 is opened, and all the exhaust gas exhausted from the cleaning tank 1 through the depressurization exhaust line 14 in the depressurization step is collected and stored in the gas storage tank 30.
In the exhaust gas recovered in the exhaust gas return line 35, sodium vapor and mist contained in the exhaust gas are removed by the vapor trap 12 on the way. Then, when shifting to the preheating step of the next cleaning cycle, the valves 33 and 34 are opened and the blower 31 is operated to circulate the inert gas stored in the gas storage tank 30 with the inert gas. Sent into line 8 and cleaning tank 1,
In this state, the preheating process and the depressurizing process described above are performed to wash the spent fuel assembly. When radioactive contamination becomes extremely high due to repeated use of inert gas, or when the operation of cleaning equipment is stopped, the gas remaining in the system is transferred to the gas waste treatment system through the decompression exhaust line. When the cleaning process is restarted after being sent out, the inert gas source 9 newly supplies the inert gas. As is clear from the above description, the exhaust gas exhausted from the cleaning tank 1 in the depressurizing step during the previous cleaning is directly sent to the gas waste processing system 13 without being processed, and the gas storage tank of the exhaust gas return line 35 is processed. It is recovered in 30 and returned to the inert gas circulation line 8 in the preheating step for the next cleaning to be activated again, so that the amount of gas waste generated in the normal cleaning cycle and the inert gas source 9 The amount of gas replenished newly to the inert gas circulation line is almost eliminated, and economical operation can be achieved including reduction of the load on the gas waste treatment system. In comparison with the illustrated embodiment, a preheating device for the spent fuel assembly is separately provided in the preceding stage of the cleaning tank to reduce the heat load of the preheating process performed in the state of being housed in the cleaning tank, and to improve the cleaning time. It can be shortened.

【The invention's effect】

As described above, according to the present invention, the exhaust gas return line is connected to connect the decompression exhaust line connected to the cleaning tank and the inert gas circulation line, and the exhaust gas return line is the decompression exhaust line. A gas storage tank for temporarily storing the exhaust gas from the gas storage tank and a blower for supplying the stored gas in the gas storage tank to the inert gas circulation line, and the exhaust gas exhausted from the cleaning tank in the depressurizing step during cleaning is By supplying to the inert gas circulation line through the exhaust gas return line, the amount of gas waste generated by cleaning the spent fuel assembly and the amount of gas newly replenished from the inert gas source during preheating Can be significantly reduced,
In this way, more economical operation can be performed while reducing the load of gas waste treatment.

[Brief description of drawings]

FIG. 1 is a system diagram of a spent fuel assembly cleaning facility according to an embodiment of the present invention, and FIG. 2 is a conventional dry reduced pressure cleaning facility system diagram. In the figure, 1: cleaning tank, 3: spent fuel assembly, 4: blower, 5: gas heater, 8: inert gas circulation line, heated inert gas circulation line that also serves as ventilation means, 9: non Active gas source, 14: decompression exhaust line, 18: sodium drain line, 30: gas storage tank, 31: blower, 35: exhaust gas return line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kobayashi 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 within Fuji Electric Co., Ltd. (56) Reference JP-A-57-86800 (JP, A) JP-A-55-46122 (JP, A) JP-A-57-146199 (JP, A) JP-A-57- 86799 (JP, A) Actual development Sho 54-111967 (JP, U)

Claims (1)

[Claims] 1. A cleaning device for a spent fuel assembly of a nuclear reactor, which uses a liquid metal such as sodium as a primary coolant, which is provided in a cleaning tank for containing the spent fuel assembly. The cleaning is carried out by connecting an inert gas circulation line that preheats the spent fuel assembly to a predetermined temperature by ventilating a heated inert gas and a decompression exhaust line that decompresses the atmosphere in the cleaning tank. In the one in which the liquid metal adhering to the spent fuel assembly is vaporized and removed for cleaning by preheating the spent fuel assembly housed in the tank and then decompressing the inside of the cleaning tank, An exhaust gas return line is connected to connect the reduced pressure exhaust line and the inert gas circulation line, and the exhaust gas return line is a gas storage tank for temporarily storing the exhaust gas from the reduced pressure exhaust line,
A blower for supplying the stored gas in the gas storage tank to the inert gas circulation line, and supplying the exhaust gas exhausted from the cleaning tank in the depressurization step during cleaning to the inert gas circulation line through the exhaust gas return line. A cleaning device for a spent fuel assembly, characterized in that