A radioactive coolant water leak at one of the idled reactors at the Takahama nuclear plant in Fukui Prefecture was caused by insufficient tension of a bolt in a valve installed in a pipe, according to Kansai Electric Power Co.
The power company said earlier that an estimated 34 liters of coolant water leaked Saturday in a building attached to the No. 4 reactor. It said Monday that the radioactivity level was below that which requires notifying the government.
Kansai Electric’s efforts to prepare the reactor for a restart have been put on hold since the leak was discovered.
It would be the fourth reactor in Japan to come back online under stricter safety rules set after the 2011 Fukushima crisis.
The No. 4 unit is also expected to become the second reactor to run on uranium-plutonium mixed oxide (MOX) fuel under post-Fukushima regulations.
MOX fuel is a key component of the nuclear fuel cycle program pursued by the nuclear power industry and the government. It is created by plutonium and uranium extracted from spent nuclear fuel.
The No. 3 reactor at the Takahama complex was brought back online in January.