Monju sodium to be processed in the UK

Wednesday, 3 May 2023

Supported by International Nuclear Services Japan - a subsidiary of the UK's Nuclear Decommissioning Authority - and working with delivery partner Jacobs, the contract will see the design, construction, operation and ultimate dismantling of a new facility in the UK, for the treatment of sodium from Monju that will be recycled for industrial use.

Cavendish, a subsidiary of Babcock International Group, has been involved in the ongoing decommissioning of the fast reactors at the UK's Dounreay site. In August 2019, the company was awarded a contract by JAEA to support decommissioning of Monju by providing technical support for creating a lifetime plan for the decommissioning of the reactor and a feasibility study into the treatment of sodium coolant from the Monju site.

"The award highlights Cavendish Nuclear's expertise in complex decommissioning projects in the UK and internationally," the company said. "It also builds on Cavendish Nuclear's long relationship with the wider Japanese nuclear industry and draws on our experience of the UK's Dounreay PFR decommissioning programme, which is similar in design to the Monju reactor."

"This contract not only supports decommissioning in Japan, it acknowledges Cavendish Nuclear's expertise in specialist nuclear decommissioning projects and will provide opportunities for our skilled nuclear engineers and many more across the wider UK supply chain for this 10-year programme," said Babcock Group CEO David Lockwood.

JAEA President Masanori Koguchi added: "It is encouraging that JAEA can now engage in this important project with Cavendish Nuclear and Jacobs which have a high level of technology based on their experience in the UK. JAEA wishes that the relationship between us will be further enhanced."

A key part of Japan's nuclear energy programme, the 280 MWe Monju FBR in Tsuruga City, Fukui Prefecture, initially started in 1994. However, it was shut down the following year, just four months after grid connection, when about 700 kilograms of liquid sodium leaked from the secondary cooling loop. Although there were no injuries and no radioactivity escaped plant buildings, the operator tried to conceal the scale of the damage. It eventually restarted in May 2010 but has not operated since refuelling equipment fell into the reactor vessel during a refuelling outage later that year. The equipment was subsequently retrieved and replaced but the Nuclear Regulation Authority (NRA) did not permit the reactor to restart.

In November 2015, following concerns over equipment inspections, the NRA determined JAEA was not competent to operate the reactor. In December 2016, the government formally announced its decision to decommission the idled Monju reactor.

The decommissioning of Monju will take 30 years and cost more than JPY375 billion (USD2.5 billion), the government estimates. This includes JPY225 billion for maintenance, JPY135 billion for dismantling the plant and JPY15 billion for defuelling and preparations for decommissioning.

JAEA submitted a detailed plan to decommission Monju, in line with the government's basic policy, to the NRA in December 2017. The plan comprised four stages. In the initial stage, JAEA would transfer all fuel to an on-site storage pool by fiscal 2022. In the second and third stages, the liquid sodium coolant will be extracted from Monju and related equipment will be dismantled. The reactor building will be demolished and removed by fiscal 2047 in the final stage. The NRA approved that plan in March 2018.

In October 2022, JAEA announced that all the fuel assemblies at Monju had been transferred to a water-filled storage facility.