Tokyo Electric Power Co. has restarted cooling systems at Fukushima Daiichi spent fuel pools following an electrical outage that TEPCO suspects might be connected to a dead rodent found near a switchboard.

Developments over the last week at the Japanese nuclear plant blacked out following the 2011 earthquake and tsunami include:

Power Restored at SFPs

Rodent near a disabled switchboard at Fukushima Daiichi. Source: TEPCOAn electrical system failure took several safety systems at the plant offline Monday, including power at the plant's emergency center and cooling systems for four spent fuel pools. Some of the safety systems were shut down manually to protect pumps and other equipment, according to a TEPCO release. Water injection into reactor cores was not suspended, and power was quickly restored at the emergency center, followed by SFP cooling at units 1, 3 and 4 on Tuesday. Cooling of the common spent fuel pool resumed just after midnight Wednesday. None of the pools approached unsafe temperatures during the outage.

Also on Wednesday, workers found soot on the walls of a temporary switchboard for units 3 and 4, TEPCO said in a release, as well as the remains of an animal that appeared to be a rat.  It's possible the rat may have contacted live circuits in the equipment, causing them to short out, although TEPCO has yet to make any conclusions on the incident.

Ohi Reactors Will be Allowed to Run Until Sept.

Only two Japanese reactors are in operation as the country redraws its regulatory scheme and plans to inspect plants to ensure compliance with the new rules. But because they were online before the new nuclear oversight body came into existence, units 3 and 4 at Kansai Electric Power Co.'s Ohi plant will be allowed to run until their next scheduled outage in September. The Nuclear Regulation Authority announced the exception on Wednesday, according to a report in The Japan Daily Press.

Ground Fish Caught With Record Cesium

TEPCO said a greenling was caught in the manmade harbor next to the plant last week with cesium levels measured at 740,000 becquerels per kilogram – the highest level found in marine life since the accidents. The Asahi Shimbun reported that the contamination amounted to 7,400 times the Japanese government limit for food.