JPH0814637B2 - Cleaning method and cleaning device for spent fuel assembly - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a method and apparatus for cleaning a spent fuel assembly for a spent fuel assembly of a fast breeder reactor that uses liquid metal such as sodium as a primary coolant.

[Prior art]

FIG. 2 is a schematic configuration diagram showing a fuel handling device of a fast breeder reactor. In FIG. 2, after the spent fuel assemblies taken out from the reactor 24 by the fuel exchanger 13 are stored in the in-reactor fuel storage rack provided in the reactor 24 to reduce the decay heat level. The spent fuel assemblies taken out of the reactor 24 by the fuel inlet / outlet unit 14 and taken out through the relay tank 15 are transferred in the argon gas cell 11 filled with argon gas to prevent the reaction of adhering sodium. The machine 10 delivers it to the cleaning tank 2 provided under the cell floor for cleaning. The spent fuel assemblies that have been washed are canned by the canning device 16 and transferred by the underground trolley 17, and further transferred by the water pool chamber fuel transfer device 18 and stored in the water pool storage rack 19 to the reprocessing plant. It is stored until it is shipped. Further, the means for carrying out the spent fuel assembly to the reprocessing plant is taken out from the storage rack 19 by the water pool chamber fuel transfer machine 18, taken by the crane 20 via the cask connection device 21, and the cask cart 22.
It is handed over to the port facility. As a method of cleaning the spent fuel assembly in this process, conventionally, the spent fuel assembly is accommodated in a cleaning tank, a wet gas containing steam is sprayed onto the spent fuel assembly, and then it is used after cleaning with water. A steam-water washing method of drying the spent fuel assembly with warm air or the like has been generally adopted. However, in this cleaning method, a large amount of radioactive waste liquid is generated, so that there is a problem that the waste liquid treatment facility becomes large. On the other hand, as an alternative to the conventional steam-water cleaning method,
A dry cleaning method has been proposed in which liquid metal adhering to a spent fuel assembly is removed without generation of radioactive waste liquid. This dry cleaning method is a decompression cleaning method of preheating a spent fuel assembly to a temperature equal to or higher than the melting point of a liquid metal such as sodium, and then depressurizing the atmosphere as a cleaning process or an inert gas heated at a high temperature. This is a high temperature gas cleaning method performed by blowing. On the other hand, as a method for preheating a spent fuel assembly in the above-mentioned dry cleaning method, the inventor uses a decay heat generated by the spent fuel assembly to raise the temperature to a preheating temperature, and a cleaning tank containing the spent fuel assembly. In contrast, a high-temperature gas preheating method in which an inert gas heated from the outside is blown to the spent fuel assembly, and a heater is installed around the cleaning tank, and the inert gas sealed in the cleaning tank is used as a heat medium. Various preheating methods such as a heater preheating method for heating a spent fuel assembly were tried.

[Problems to be Solved by the Invention]

As is well known, the fuel assembly is a structure including a fuel pin that generates decay heat, upper and lower bracket portions surrounding the fuel pin, and a non-heat generating portion such as a trumpet tube. In the preheating method by self-decay heat,
The amount of heat generated by the decay heat is small, and the heating rate is as low as about several degrees centigrade / minute even in the vicinity of the fuel pin, which is the heat generating portion, and the silencing of the non-heat generating portion away from the fuel pin is insufficient. Further, the high-temperature gas blow preheating method requires a large-scale gas circulation loop, and since the heat capacity of the gas as a heat medium is small, preheating takes a relatively long time. Further, the heater preheating method has a problem that the heating efficiency is low and it takes a long time to preheat, and it has been found that there is a problem in efficiently preheating the entire area of the spent fuel assembly in a short time. Further, the removed liquid metal was recovered by a vapor trap installed in a depressurization system or a gas circulation system, and it was found that a dedicated large-sized storage tank was necessary. The present invention is a method and a method for cleaning a spent fuel assembly capable of heating a spent fuel assembly to a predetermined preheating temperature in a short time and recovering the removed liquid metal without requiring a large storage tank. The purpose is to provide a device.

[Means for Solving the Problems]

The above-mentioned purpose is to take out the spent fuel assembly from the reactor to the outside, transfer it to a cleaning tank under the floor of the argon gas cell, and store the spent fuel assembly in a pot arranged below the cleaning tank to remove the spent fuel assembly. The fuel assembly is immersed in the liquid metal in the pot, the liquid metal in the pot is heated by a heater arranged around the cleaning tank, and the spent fuel assembly is preheated by the liquid metal. In the cleaning tank, the heating gas is blown from above the spent fuel assembly in a state where the spent fuel assembly is pulled up from the pot, and the liquid metal attached to the spent fuel assembly is cleaned, This is achieved by a method for cleaning a spent fuel assembly, in which most of the liquid metal attached to the spent fuel assembly is collected in the pot. Further, the above-mentioned object is arranged in a cleaning tank below the floor of an argon gas cell, a pot for filling the inside with a liquid metal and containing the spent fuel assembly, and a liquid metal in the pot arranged around the cleaning tank. A preheating means consisting of a heater for heating, a blower for circulating the argon gas in the argon gas cell, a gas heater for heating the argon gas, a vapor trap for removing the liquid metal in the argon gas, and a gas cooler. And a cleaning device comprising a cleaning means for cleaning the spent fuel assembly.

According to the present invention, a pot containing liquid metal is installed in the cleaning tank, a heater is arranged on the outer periphery of the cleaning tank, the liquid metal in the pot is heated by the heater, and the liquid metal in the pot is heated. The spent fuel assembly can be preheated by immersing the spent fuel assembly in. Also, with the spent fuel assembly pulled up to the top of the pot, the inert gas heated to high temperature can be blown to remove the liquid metal adhering to the spent fuel, and the removed liquid metal can be removed from the pot. Since most of the activated liquid metal is transferred to the gas circulation system, the amount of the activated liquid metal transferred to the gas circulation system can be reduced. The cleaning device according to the present invention is arranged in a cleaning tank, and a preheating means including a pot filled with the liquid metal inside and a heater arranged around the cleaning tank is used to collect spent fuel assembly in the liquid metal in the pot. The body can be soaked and preheated. Furthermore, a blower that circulates the argon gas, a heater that heats the argon gas, and a cleaning means consisting of a vapor trap and a gas cooler are used to blow the high-temperature argon gas while the spent fuel assemblies are suspended. Most of the liquid metal that has been cleaned and removed from the spent fuel assembly can be collected in the pot.

【Example】

FIG. 1 is a system diagram of a cleaning device used in a method of cleaning a spent fuel assembly according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a fuel handling device of a fast breeder reactor. In FIG. 2, the spent fuel assembly 1 is taken out of the core by the fuel exchanger 13 and stored in the in-core fuel storage rack to reduce the decay heat level. The spent fuel assembly taken out to the outside and passed through the relay tank 15 is an argon gas cell filled with an inert argon gas to prevent the liquid metal adhering to it from being oxidized.
The inside of 11 is transferred by the in-cell crane 10 to the cleaning tank 2 provided under the floor of the cell. First, a method of cleaning a spent fuel assembly according to an embodiment of the present invention will be described. In FIG. 1, the spent fuel assembly 1 is taken out of the reactor 24 by the fuel inlet / outlet device 14 and transferred to the relay tank 15, and then transferred from the relay tank 15 to the cleaning tank 2 under the argon gas cell 11 by the transfer device 10, The spent fuel assembly 1 is housed in a pot 3 arranged below the cleaning tank 2, and the spent fuel assembly 1 is immersed in the same liquid metal 4 as the primary coolant in the pot 3, The liquid metal 4 in the pot 3 is heated by the heater 5 arranged around the liquid metal 4
The spent fuel assembly 1 is preheated by. It is also possible to use induction heating for the external heater 5. The spent fuel assembly 1 heated in the pot 3 is lifted above the pot 3 by the in-cell crane 10 and lifted in the cleaning tank 2. In this state, the blower 7 and the gas heater 9 outside the cleaning tank 2 are operated, and the heated inert gas is blown to the spent fuel assembly 1 to evaporate and remove the adhering liquid metal. The liquid metal removed at this time is
It is discharged from the entrance nozzle of the spent fuel assembly 1, most of it is collected in the lower pot 3, and part of it enters the gas circulation line and is collected in the vapor trap 6. After evaporating and removing the liquid metal, the operation of the gas heater 9 is stopped, and the low-temperature inert gas cooled by the cooler 8 is blown to the spent fuel assembly 1, whereby the spent fuel assembly 1
To cool. After cooling, the spent fuel assembly 1 is transferred to the underground trolley 17 by the in-cell crane 10 in FIG. 2 and is further stored in the spent fuel storage rack 19 in which water is pooled by the water pool chamber fuel transfer device 18. Transported and stored until shipped for improved reprocessing. Next, a cleaning device for a spent fuel assembly according to an embodiment of the present invention will be described. Referring to FIG. 1, a cleaning device for a spent fuel assembly according to an embodiment of the present invention is arranged in a cleaning tank 2 under a floor of an argon gas cell 11 and filled with liquid metal to accommodate the spent fuel assembly 1. Pot 3
And the liquid metal 4 in the pot 3 arranged around the cleaning tank 3.
A preheater including a heater 5 for heating the gas, a blower 7 for circulating the argon gas in the argon gas cell 11, a gas heater 9 for heating the argon gas, and a vapor trap 6 for removing the liquid metal in the argon gas, Gas cooler 8
And a cleaning means including a check valve 12. The spent fuel assembly 1 is first preheated by the liquid metal heated by being immersed in the pot 3, and then lifted up by the transfer machine 10 and blown with heated argon gas in the lifted state, so that the spent fuel assembly 1 is The liquid metal 4 attached to is evaporated and removed.

【The invention's effect】

As described above, in the method for cleaning the spent fuel assembly according to the embodiment of the present invention, the spent fuel assembly is immersed in the liquid metal in the pot arranged below the cleaning tank, and is disposed around the cleaning tank. The heated metal heats the liquid metal in the pot by preheating the spent fuel assembly with the liquid metal, and then the heated gas is spent fuel in the cleaning tank with the spent fuel assembly pulled up from the pot. By blowing air from above the assembly to wash the liquid metal adhering to the spent fuel assembly and recovering most of the liquid metal adhering to the spent fuel assembly to the pot, it is possible to shorten the time. Since the spent fuel assembly can be heated to a predetermined preheating temperature and the amount of liquid metal recovered by the vapor trap is reduced, the storage tank capacity dedicated to the vapor trap can be reduced. A spent fuel assembly cleaning apparatus according to an embodiment of the present invention includes a pot for filling a liquid metal therein and containing a spent fuel assembly, and a heater arranged around a cleaning tank for heating the liquid metal in the pot. A preheating means consisting of, a blower that circulates the argon gas in the argon gas cell, a gas heater that heats the argon gas, a vapor trap that removes the liquid metal in the argon gas, and a cleaning means that includes a gas cooler. Since it is provided, the spent fuel assembly can be preheated by the heated liquid metal in a short time, and immediately after that, the heated argon gas is blown in the cleaning tank to clean the spent fuel assembly.

[Brief description of drawings]

FIG. 1 is a system diagram of a cleaning device used in a method of cleaning a spent fuel assembly according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a fuel handling device of a fast breeder reactor. 1: Spent fuel assembly, 2: Cleaning tank, 3: Pot, 4: Liquid metal, 5: Seater, 6: Vapor trap, 7: Blower, 8: Gas cooler, 9: Gas heater, 10: Transfer Machine, 11: Argon gas cell, 24: Reactor.

Claims (2)

[Claims] 1. A method for cleaning a spent fuel assembly of a nuclear reactor, which uses a liquid metal such as sodium as a primary coolant, in which the spent fuel assembly is heated to a predetermined temperature by a preheating means and preheated. Then, the heated gas is blown to the spent fuel assembly while the spent fuel assembly is housed in the cleaning tank to evaporate and remove the liquid metal adhering to the spent fuel assembly. In the cleaning method for cleaning, the spent fuel assembly is taken out of the nuclear reactor, transferred to a cleaning tank under the floor of the argon gas cell, and the spent fuel assembly is placed in a pot arranged below the cleaning tank. The liquid fuel in the pot is housed and the spent fuel assembly is immersed in the liquid metal in the pot, and the liquid metal in the pot is heated by a heater arranged around the cleaning tank to remove the spent fuel assembly by the liquid metal. Preheat After that, the heating gas is blown from above the spent fuel assembly in a state where the spent fuel assembly is pulled up from the pot in the cleaning tank to clean the liquid metal attached to the spent fuel assembly. At the same time, most of the liquid metal attached to the spent fuel assembly is collected in the pot, and the method for cleaning a spent fuel assembly is characterized. 2. A device for cleaning a spent fuel assembly of a nuclear reactor, which uses liquid metal such as sodium as a primary coolant, and preheats the spent fuel assembly to a predetermined temperature by preheating means. Then, the heated gas is blown to the spent fuel assembly while the spent fuel assembly is housed in the cleaning tank to evaporate and remove the liquid metal adhering to the spent fuel assembly. In a cleaning device for cleaning, a pot is arranged in a cleaning tank below the floor of an argon gas cell, and a pot is filled with a liquid metal to accommodate the spent fuel assembly; and a pot arranged around the cleaning tank in the pot. Preheating means consisting of a heater for heating the liquid metal, a blower for circulating the argon gas in the argon gas cell, a gas heater for heating the argon gas, and removing the liquid metal in the argon gas. And a bar-Pas trap, the cleaning apparatus of the spent fuel assemblies, characterized in that a cleaning means consisting of a gas cooler.