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Murky start as lack of experience plagues Monju decommissioning

Japan Atomic Energy Agency (JAEA) President Toshio Kodama, foreground, speaks to JAEA staff before the organization starts the removal of nuclear fuel from the Monju nuclear reactor as part of its decommissioning process in Tsuruga, Fukui Prefecture, on Aug. 30, 2018. (Mainichi)

TSURUGA, Fukui -- The Japan Atomic Energy Agency (JAEA) began the removal of nuclear fuel from the Monju prototype fast-breeder nuclear reactor here Aug. 30 -- the first significant step in the reactor's decommissioning process, which is expected to take 30 years.

Because of a difficult-to-handle coolant and the lack of experience among workers, the road to a decommissioned reactor is expected to be an extremely bumpy one. And with the prospects of developing a successor reactor unclear, the city of Tsuruga, which as a host city of the reactor has depended on nuclear power, now stands at a crossroads.

"We now stand at the true starting line," JAEA President Toshio Kodama said Aug. 30. "Carrying the process out safely and steadily will allow us to earn the confidence of the local community."

One reason for the extreme difficulty of the Monju's decommissioning is the use of liquid sodium as a coolant. The opaque substance ignites when exposed to air, and causes an explosive chemical reaction when it comes in contact with water. Due to such characteristics, the decommissioning process must be carried out via specialized equipment that allows for remote operation with the coolant kept in its sealed state, or, as one senior official with the Secretariat of the Nuclear Regulation Authority said, with the "supernatural" ability to control multiple pieces of equipment with millimeter-scale accuracy without being able to see what's going on.

There are a total of 530 nuclear fuel rods, which are lined up supporting each other within the reactor core. Every time a rod is taken out, a replacement mock rod must be put in its place.

Since there have only been two past cases in which nuclear fuel has been removed from reactor cores, the lack of experience among workers is also of grave concern. Due to such factors as the leak of molten sodium from the reactor in 1995, Monju has only been operated for 250 days. Many have resigned from the project, and of the 55 people who will be taking part in the fuel removal during peak periods, only about 10 have experience operating the reactor.

JAEA has repeated simulated training using maps and mock facilities, but problems have arisen one after another, such as sodium coolant getting stuck and steam fogging up monitoring cameras during a test run of equipment. The organization was able to stick to the promise it made to the local community that it would start Monju's decommissioning process in August, but there is no denying a sense that the work is off to a hasty start with various concerns still unanswered and unresolved.

In the second phase of decommissioning set to start in the 2023 fiscal year, approximately 760 metric tons of sodium that is in contact with nuclear fuel will be removed from the reactor. Work to remove a portion of the hundreds of tons of sodium that fills the reactor vessel, however, is predicted to be especially challenging, due to the vessel's design. Not only will it require the development of new technology, but no decision has been made as to how and where the sodium will be disposed of.

"Japan should explore collaborating with highly experienced specialized decommissioning companies abroad, placing ultimate priority on not causing a major incident," urged Isamu Sato, a professor of nuclear safety engineering at Tokyo City University.

Meanwhile, the Japanese government, which upholds the nuclear fuel cycle as a national policy, is aiming to develop a fast reactor to succeed the failed Monju fast-breeder reactor, and is hoping to keep joint Japanese-French research on ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration), a French demonstration sodium-cooled fast-breeder reactor project, front and center.

France, however, announced in June that it would drastically reduce ASTRID's predicted output from its initially planned 600,000 kilowatts to around 100,000 to 200,000 kilowatts. If this ends up being the case, the scale of Monju's successor will be smaller than Monju, whose output was 280,000 kilowatts, meaning that Japan now faces the possibility that it will not be able to obtain data that will contribute to creating a fast reactor with commercial viability.

The Japanese and French governments have thus far agreed to conduct research together until the end of next year, but promises for collaboration in 2020 and beyond have not yet been made. Japan is planning to draw up a time schedule before the end of the year, at the earliest, for the development of a fast breeder with France's cooperation post-2019, taking into account the scaling back of the reactor's output volume, but the nuclear fuel cycle is increasingly looking like it might be just a pie in the sky.

(Japanese original by Toshiyuki Suzuki and Ei Okada, Science & Environment News Department)

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