The Kyushu Electric Power Company said that it discovered problems with the cooling system at the Sendai No. 1 reactor that was restarted last week, creating more potential controversy for the first nuclear reactor to power up following a prolonged nationwide nuclear power moratorium.
Until last week, the Sendai No. 1 reactor had not been operating for more than four years. It was shut down following the March 2011 disaster at the Fukushima Daiichi nuclear power plant 180 northeast of Tokyo. The triple-reactor meltdown at Fukushima was caused by the tsunami event that shut down the plant's back up power system following the Great East Japan Earthquake.
Last week, after the No. 1 reactor at Sendai was restarted, geologists warned of potential volcanic activity in the region, which put Japan on alert, but did not result in a plant shut down.
But plant engineers said that seawater had likely entered one of the pumps in the plant's secondary cooling system, which set off alarms at 75 percent power and caused the delay of a scheduled output increase. The small amount of seawater had flowed into one of three steam to water condensers, each of which has 26,000 tubes that contain seawater for cooling. Plant operators said they suspect holes in some tubes had opened, allowing seawater to enter the condenser, the Japan News reported.
The reactor's output was to be bumped to 95 percent on Friday and full power was expected by 25 August. But that has been delayed by the problems that plant operators say could take a week to repair.
Sendai's reactor No. 2 is scheduled for restart by the end of the year.