The Nuclear Regulation Authority approved on Wednesday a decommissioning plan for the Monju fast breeder reactor in Tsuruga, Fukui Prefecture, submitted by the Japan Atomic Energy Agency (JAEA).
Specifically, the nuclear regulator approved the implementation of the plan's first stage, to be carried out from fiscal 2018 to fiscal 2022, to remove nuclear fuel from the reactor. Following the approval, the JAEA is set to begin work to remove nuclear fuel in July, launching the 30-year-long decommissioning process.
The plan divides the process into four stages. There are a total of 530 nuclear fuel rods in fuel storage pools located in and outside the reactor. In the first stage, the JAEA will start transferring 100 rods located outside the reactor to a fuel pool before the end of the year, eventually moving all the rods to the pool by fiscal 2022.
It is the first time in Japan for a fast breeder reactor to be decommissioned. All the work, including demolishing the facilities, is expected to be completed by fiscal 2047, at a total cost of about 375 billion yen.
In the second and third stage, the JAEA will work to extract the liquid sodium used as a coolant, which is contaminated with radioactivity, and dismantle related equipment. This will be followed by demolition and removal of the reactor building in the fourth stage.
A nuclear fuel in-vessel transfer machine will be used for removing the fuel rods, but the JAEA has only ever taken out and transferred two fuel rods -- in 2008 and 2009 -- and the education and training of frontline staff has become a challenge. An accident also occurred in 2010 where the transfer machine fell into the reactor. Precision down to the millimeter is required to grab and pull the rods with the machine.
Another difficulty is removing the sodium. Sodium reacts violently with air and water. Therefore, the work must be performed within a sealed space using a device by remote control.
Meanwhile, the government needs to lay out a path to dispose of spent fuel and radioactive sodium along with the JAEA, after removing it from the reactor. Plutonium-uranium mixed oxide (MOX) fuel in the Monju reactor contains a higher rate of plutonium than MOX fuel used in ordinary nuclear power plants, and there is no facility in Japan that can reprocess the fuel.
It appears realistic to hand off the task to a facility overseas, but transportation of plutonium requires rigid international control due to concerns that it can be diverted to atomic weapons.
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