Cavendish and Jacobs sign MOU for UK treatment of Japanese fast reactor sodium coolant

6 January 2022

Monju was permanently shut down in 2010Cavendish Nuclear and Jacobs have signed a Memorandum of Understanding with Japan Atomic Energy Agency (JAEA) for the treatment and re-use in the UK of sodium coolant from Japan’s Monju fast neutron reactor, which ceased operations in 2010.

Cavendish said the material “is not of significant radiological concern but it requires careful treatment to minimise the hazards associated with reactive alkali metal”. Jacobs and Cavendish Nuclear will apply their knowledge and experience from previous sodium coolant treatment projects to deal with the material safely and effectively.

JAEA, citing a number of Japanese press reports in late December said the "removal of sodium during Monju decommissioning work requires development of new equipment." The reactor vessel and piping of the prototype fast breeder reactor contained more than 1660 tons of sodium coolant. During decommissioning about 77 tons could not be extracted with existing equipment and remains on the bottom of the piping and equipment.  

The policy is to develop new equipment to extract it. An investigation showed that there is about 1 ton of sodium that cannot be extracted from the reactor vessel. Some 50 of about 905 tons of primary sodium that contains radioactive substances has not been removed, while 27 tons of the approximately 755 tons of secondary sodium that does not contain radioactive substances still remains. The total amount of sodium that cannot be extracted in Monju was first clarified during a monitoring team meeting in December. However, the figures are currently being estimated and are not final.

Photo: The Monju fast reactor in Japan

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