Monju back after 14 years

06 May 2010

Fourteen years and five months after it was shut down by a major coolant leak, Japan's 280 MWe Monju fast-breeder reactor (FBR) resumed operations today.


After receiving final confirmation from the local and national governments, the reactor was restarted to low power levels in a process completed at 10.36 am local time, according to the Japan Atomic Energy Agency (JAEA).


"The procedures all went according to plan and this is the final step in a process that has focused strongly on safety," said Daisuke Iizuka, a spokesman for the agency. The reactor should reach "critial levels" by 8 May. It will undergo many tests before going into full commercial operation in 2014.


Monju (JAEA)
Monju (Image: JAEA)

The prototype reactor - whose name is Japanese for wisdom - uses plutonium fuel instead of conventional uranium and is configured to produced fissile matter that can be reused as fuel, hence the term 'breeder'. The project was first proposed in the late 1960s as an antidote to Japan's reliance on imported energy to feed its industries. While Japan's 54 nuclear power reactors rely on small volumes of uranium, this too must be imported and so the use of FBRs to stretch out extend the resource is very attractive. Monju came after the Joyo experimental FBR, that has operated since 1977.


A key part of Japan's nuclear energy program, Monju initially started in August 1995, but was shut down only four months later after a serious incident. About 700 kilograms of liquid sodium leaked from the secondary cooling loop and, although there were no injuries and no radioactivity escaped plant buildings, this was compounded by operator attempts to cover up the scale of the damage which could have been reduced by better design and quicker action.


The JAEA has carried out a thorough review of the design of the plant, as well as safety procedures, which were shown to have been inadequate. According to the agency, the design changes include replacing the thermocouple well with a shorter and tapered version that reduces vibrations caused by liquid flows, modification of the sodium drain circuit, improving the reliability of the system to detect leaks and upgrading the evaporator blow-down system for stream leakage.


The agency admits that 14 years was longer than it had anticipated before it was able to restart the plant. "But there were several reasons for taking that amount of time," Iizuka said. "The main obstacles were the safety inspections - including seismic safety checks - the modifications to the reactor and carrying out new checks of every component in the plant. "It also took time to win the support of the local governor and residents," he admitted.


In the last ten years, the JAEA has held more than 1000 meetings with people living in an around the town of Tsuruga, in the prefecture of Fukui, and some 40,000 local residents have taken part in guided tours of Monju.


The operators of the plant say Monju will reach critical levels on Saturday and test runs will continue before it goes into full operation in 2014. Japan aims to put fast-breeder reactors into commercial use around 2050.


By Julian Ryall
for World Nuclear News