Decommissioning starts at Monju

August 30, 2018

Work starts to decommission problem-plagued Monju reactor

http://www.asahi.com/ajw/articles/AJ201808300045.html

THE ASAHI SHIMBUN

The Japan Atomic Energy Agency (JAEA) on Aug. 30 started work to decommission the Monju prototype fast-breeder reactor in Fukui Prefecture, a once-promising project that struggled with problems, even in preparations for its dismantlement.

The work started a month later than scheduled because of a series of equipment trouble. The JAEA workers also face an enormous challenge because Japan has no experience in decommissioning a fast-breeder reactor.

The JAEA will use overseas experiences as a reference for the delicate process.

Before the start of the work, JAEA President Toshio Kodama told staff members in a speech at the plant in Tsuruga, “I want you to tackle this work by bracing yourselves.”

Monju had been a key facility in the government’s nuclear fuel recycling program.

Construction of the reactor started in 1985, but a series of accidents, including a sodium coolant leak in 1995, as well as cover-ups kept the reactor offline for most of its life.

In 2016, after 1 trillion yen ($9 billion) had been spent on the project, the government finally decided to abolish Monju.

The decommissioning work is scheduled to take 30 years and cost 375 billion yen.

One of the riskiest parts in the decommissioning process is handling the liquid sodium, which reacts strongly with water and air.

In the first of the four-stage decommissioning project, the JAEA will transfer 530 nuclear fuel assemblies, currently kept in the liquid sodium-filled nuclear reactor and storage tank, to a water-filled pool by fiscal 2022.

In the work that began on Aug. 30, the JAEA will remove 160 nuclear fuel assemblies from the storage tank, wash away the sodium, and place them in the pool.

From 2019, the agency will transfer nuclear fuel assemblies from the reactor to the storage tank and then to the pool.

In December this year, the JAEA will also start to transfer about 760 tons of sodium, which has not been exposed to radioactive substances, to its storage tank. Later, the agency will remove about 910 tons of radioactive sodium from the reactor and other equipment.

In the following stages, the agency will dismantle the nuclear reactor, the turbine and other facilities.

However, no decision has been made on how to dispose of the nuclear fuel removed from the reactor and the storage tank. Monju has used mixed oxide (MOX) fuel, which contains plutonium and currently cannot be reprocessed in Japan.

“It’s realistic to ask an overseas company to reprocess it,” said Toyoshi Fuketa, chairman of the Nuclear Regulation Authority, the government’s nuclear watchdog.

If reprocessing expenses in a foreign country are added, the overall decommissioning costs will sharply increase.