Fast-breeder reactor Monju's decommissioning work begins with fuel removal

TSURUGA, Fukui -- The removal of nuclear fuel from the crippled fast-breeder reactor Monju began on Aug. 30 here as the first step in its 30-year-long, unprecedented decommissioning process.

It will take at least until fiscal 2022 to remove 530 fuel rods from the core and the fuel cooling pool of the prototype reactor in this central Japan city of Tsuruga in Fukui Prefecture. Maintaining the safety for workers is one of the main challenges of the difficult decommissioning process for the 1-trillion-yen experimental reactor.

Monju, named after a Buddhist deity of wisdom, was originally touted as a "dream reactor" capable of producing more nuclear fuel than it consumes, but has ended up a failure due to a series of accidents and repeated trouble.

The fuel removal work began with a speech by President Toshio Kodama of the Japan Atomic Energy Agency (JAEA), which operates the fast-breeder reactor. "I want you to make efforts to prevent trouble by paying very close attention," he said. "The real work is ahead of us. Safe and steady progress will win the trust of the local community."

A team of workers began to remove fuel at around 10:30 a.m. using specially designed remote controlled equipment. The team will remove one fuel rod, 4.2 meters long and 10 centimeters thick, from a fuel pool filled with liquid sodium, wash and pack it up in a canister, and place it inside another fuel pool filled with water. The first day's planned procedure is expected to be completed during the night if everything goes smoothly.

According to the plans, one fuel rod will be removed per day using similar procedures and a total of 100 rods will be taken out of the sodium pool by the end of this year. Fuel rods in the reactor's core will be transferred in the next fiscal year or later.

When decommissioning an ordinary nuclear power reactor, the Nuclear Regulation Authority (NRA) conducts safety checks on work plans after fuel rods are removed from the core. But the authority took the exceptional step of conducting the checks from the stage of fuel removal because the reactor has special features and the removal procedure is complex.

Monju's decommissioning will be carried out in four stages. The NRA only approved the removal of nuclear fuel that is scheduled to be completed by fiscal 2022. Plans are yet to be finalized for the second and later stages, which will include the removal of liquid sodium coolant. The JAEA will apply for the NRA's approval for decommissioning work for the later stages. The entire work of shuttering Monju is estimated to cost a total of 375 billion yen.

Monju uses a mixed oxide of plutonium and uranium and is designed to produce more plutonium than it consumes while producing electricity. The nuclear reactor was regarded as the main pillar of the nuclear fuel cycle but it suffered a massive leak of sodium coolant in 1995, just a year after it began operation, and remained closed for years. The facility has also experienced a series of trouble including a failure to conduct equipment checks, and the government decided to close it in 2016. The reactor had been in operation for a total of 250 days.

(Japanese original by Toshiyuki Suzuki, Science & Environment News Department, Kazutaka Takahashi, Tsuruga Local Bureau, and Shuichi Abe, Osaka Science & Environment News Department)