JAEA submits plan to decommission Monju

The Yomiuri Shimbun

The Yomiuri ShimbunThe Japan Atomic Energy Agency submitted its plan for decommissioning its Monju fast breeder reactor in Tsuruga, Fukui Prefecture, to the Nuclear Regulation Authority on Wednesday.

The JAEA will start its decommissioning work as soon as the plan is approved. According to the plan, the work will be completed in 30 years, or in fiscal 2047, with an estimated total cost of about ¥150 billion. The government decided to decommission the Monju reactor in December 2016.

The decommissioning plan is scheduled to involve four stages. In the first stage, 370 nuclear fuel rods will be taken out of the reactor by fiscal 2022. From the second stage onward, work such as the removal of liquid sodium coolant will be carried out, with the reactor building to be dismantled in the fourth stage.

The decommissioning of a fast breeder reactor is unprecedented in Japan and is expected to present challenges.

Unlike ordinary nuclear reactors, the Monju reactor core has a special structure in which nuclear fuel rods support each other. This makes it necessary to take out fuel rods one by one and to install mock-up fuel rods — which need to be newly manufactured — in the space that the original fuel rods used to occupy. Since liquid sodium, used as coolant for Monju, reacts strongly with water and air, removing the rods requires extreme caution.

Monju reached criticality for the first time in 1994 and started to generate power in August 1995.

However, with a sodium leakage accident in December of the latter year and a series of problems ensuing, the government decided in December last year to decommission it.

The reactor was able to generate power for only 44 days despite having over ¥1 trillion poured into operating it.Speech

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