Container and Method for Storing Spent Nuclear Fuel

Abstract

Method for long-term dry storage of spent nuclear fuel includes injecting the inert gas into a cavity formed in a cask between inner and outer lids under pressure greater than the pressure of the inert gas in the inner cavity of the cask in which the spent nuclear fuel is located. The cask contains a body with a spent nuclear fuel container placed in it, tight inner and outer lids forming a cavity into which the inert gas is pumped under pressure greater than the pressure in the inner cavity of the cask. The outer lid comprises a labyrinth hole closed with a flange and sealed with a gasket. The flange comprises an angle valve, to which at least two pressure sensors are connected. The angle valve and sensors are covered with a protective cover during long-term storage. The gasket is installed in an annular groove of the lower flange.

Claims

1. A method of prolonged dry storage of spent nuclear fuel includes the placement of the spent nuclear fuel in the inner cavity of the cask, filling the internal cavity of the cask with inert gas, sealing of the inner cask lid closing the inner cavity with spent nuclear fuel, sealing of the outer cask lid, injecting into the cavity between the outer and inner lids of the cask the inert gas under pressure greater, than the pressure in the inner cavity of the spent nuclear fuel cask, and connecting the pressure sensors to the inner side of the outer lid of the cask.

2. A spent nuclear fuel cask contains a body with a spent nuclear fuel container placed in it, tight inner and outer lids forming a cavity into which the inert gas is pumped under pressure greater than the pressure in the inner cavity of the cask, while in the outer lid there is a labyrinth hole closed with a flange and sealed with a gasket, an angle valve is installed in the flange, to which at least two pressure sensors are connected, an angle valve and sensors are covered with a protective cover during long-term storage, in the lower flange of which there is an annular groove in which the gasket is installed.

3. The cask according to claim 2 characterized in that additionally, the outer cover has a channel connected to the cavity between the outer and inner lids, sealed with a valve closed by the lid.

4. The cask according to claim 3 characterized in that during transportation of the cask and during long-term storage of the cask, the valve that shuts down the channel is closed with a blind valve cover.

5. The cask according to claim 3 characterized in that during the injection of inert gas, the valve that shuts down the channel is closed with a process cover equipped with a rod for controlling the valve and a quick-release coupling for connecting the inert gas injection system and/or a pressure gauge.

6. The cask according to claim 2 characterized in that the labyrinth hole in the outer lid is sealed with a serrated metal gasket clad on both sides with thermally expanded graphite.

7. The cask according to claim 2 characterized in that a double serrated metal gasket clad on both sides with thermally expanded graphite is installed in the annular groove.

8. The cask according to claim 2 characterized in that the protective cover has pressure-tight seals (cable glands) designed for laying cables for a continuous pressure monitoring system, sealed with a ring made of thermally expanded graphite.

9. The cask according to claim 2 characterized in that one of the sensors connected to the angle valve is a duplicate.

10. The cask according to claim 2 characterized in that pressure sensors are connected to a centralized system of continuous pressure monitoring via cable glands on the protective cover.

Description

[0034] FIG. 1 shows the outer lid in the transport position of the cask.

[0035] In the outer lid 1, a labyrinth hole 2 is made, closed by a flange with a plug 3, sealed with a metal gasket 4 and connected to the cavity 5 between the inner and outer lids. A blind valve cover 6 with a metal gasket 4 is installed above the plug 3. Also in the outer lid 1 there is a channel that connects to the cavity 5, sealed with valve 6, which is closed by a blind valve cover 7. In this position of the outer lid, the container is transported.

[0036] FIG. 2 shows the process cover.

[0037] The process cover 8 has a rod for controlling the valve 6 and a quick-release coupling 9 for connecting an inert gas injection system and/or a pressure gauge.

[0038] FIG. 3 shows the outer lid in the long-term storage position, in which sensors 13 are connected to the pressure-tight seals (cable glands) 12 from the inside of the protective cover 11.

[0039] After vacuum drying of the inner cavity of the spent nuclear fuel cask through the inner lid, according to the requirements, the inner cavity of the spent nuclear fuel cask is filled with inert gas, such as helium, which shall be in the inner cavity during long-term storage of spent nuclear fuel (60 years or more) and the inner lid is sealed. After that, the outer lid of the cask 1 is installed and sealed.

[0040] During transportation, the channel is closed with blind valve cover 7.

[0041] After delivery of a spent nuclear fuel cask to the storage facility for long-term storage, the following process operations are performed with this cask.

[0042] Cover 7 is removed, and instead of it the process cover 8 is installed and sealed (FIG. 2), which has a rod for controlling the valve 6 and a quick-release coupling 9 for connecting the inert gas injection system and/or pressure gauge. To test the tightness of the inner lid of the spent nuclear fuel cask after transportation, to the quick-release coupling 9 a pressure gauge is connected, valve 6 is opened using the rod and the pressure in the cavity between the two lids is measured (if there is a leak in the seals of the inner lid, a pressure gauge will show increased pressure). After checking the tightness of the seals of the inner lid, the pressure gauge is removed and the inert gas injection system is connected in its place through a quick-release coupling 9. Then, the blind cover 7 (FIG. 1) and the plug 3 are removed, and in place of the plug the angle valve 14 is installed (FIG. 3). Two pressure sensors 13 are connected to the angle valve 14 (one-main, the second backup). The angle valve 14 is closed and the valve 6 is opened through the rod. Inert gas is injected into the cavity 5 through a quick-release coupling 9 and a valve 6 using an inert gas injection system. When the required inert gas pressure is reached in the cavity 5, the valve 6 is closed, the inert gas injection system is turned off, the process cover 8 is dismantled and the blind cover 7 with a serrated metal gasket is installed. After testing the blind cover 7 for tightness, the valve 14 is opened. On the inside of the protective cover 11 (FIG. 3), sensors 13 are connected to the pressure-tight seals 12 (cable glands), after which the protective cover 11 is sealed with a serrated metal gasket and its tightness is checked. From the outside of the protective cover 11, cables of the centralized pressure monitoring system in spent nuclear fuel casks located in the spent nuclear fuel storage are connected to the cable glands 12.

[0043] The pressure monitoring system in spent nuclear fuel casks allows continuous monitoring of the pressure in the cavity 5 of each cask installed in the spent nuclear fuel cask storage facility, and the results are read on the storage control panel. When the threshold pressure values in the cavity 5 of a certain cask are reached, an alarm is triggered on the control panel, indicating that the sealing gaskets of a certain spent nuclear fuel cask are broken. The personnel of the storage facility should take actions to eliminate the leakage of a spent nuclear fuel cask.

[0044] The use of two pressure sensors on the nuclear spent fuel cask eliminates the risk of false alarms, for example, due to a faulty pressure sensor.

[0045] To verify or replace faulty pressure sensors, it is necessary to follow these steps:

[0046] Disconnect the cables connected to the cable glands 12 (FIG. 3) on the outside of the protective cover 11 and remove it. Disconnect the cables connected to the cable glands 12 and pressure sensors 13 on the inside of the protective cover 11. Close the angle valve 14 and remove the sensor(s). After replacing the sensors 13, open the angle valve 14, seal the protective cover 11 and connect the pressure monitoring system cables.

[0047] The claimed cask design allows for safe long-term dry storage of spent nuclear fuel from VVER-1000/1200 nuclear reactors.