The Nuclear Regulation Authority is to inspect a building at the stricken Fukushima No. 1 nuclear plant that may contain evidence proving whether it was the powerful tsunami or the earthquake that triggered reactor meltdowns.
The No. 1 reactor building houses isolation condensers, key safety devices which failed in the March 11, 2011, disaster. They should have withstood the magnitude-9.0 Great East Japan Earthquake.
"We want to begin an investigation soon," agency chairman Shunichi Tanaka said Feb. 13.
In February 2012, plant operator Tokyo Electric Power Co. lied about conditions inside the building, apparently to prevent an inspection taking place at that time.
A Diet investigation committee requested access. TEPCO replied that an inspection would be dangerous because the building was "pitch black" inside, an assertion later exposed as false.
An inspection could settle a fundamental difference of opinion between the Diet committee and a separate investigating panel set up by the government over the root cause of the disaster. The Diet committee believes it was the temblor, but the government panel says it was the tsunami.
If the condensers are found to show damage consistent with shaking in an earthquake there would be case for higher standards in nuclear plant design—with important implications for existing reactors built to lesser tolerances.
But the Nuclear Regulation Authority chairman warned against premature conclusions.
"We will not pre-judge the investigation," Tanaka said.
He added that an investigation "is essential if we are to learn full lessons from the Fukushima nuclear accident."
"We are now discussing how to approach it," he said.
However, inspecting the condensers will not be easy and investigators may find that they are unable to linger there for long. Radiation levels are extremely high inside the No. 1 reactor building. In some areas, levels are several tens of millisieverts per hour.
The NRA will now decide details of when and how the inspection should take place.
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