8 Jul (NucNet): Nuclear regulators and operators in Japan should have been aware about new sources of information showing the design basis for the protection of some nuclear power stations from tsunamis was inadequate, a former nuclear regulator has said.
Professor Shunsuke Kondo, former chairman of Japan’s Atomic Energy Commission, which was replaced by the Nuclear Regulatory Authority (NRA) in September 2012, told the International Youth Nuclear Congress in Burgos, Spain, that the Fukushima-Daiichi accident has taught the nuclear industry that nuclear power station operators should “remain vigilant” as new insights and sources of information emerge.
The NRA is now asking nuclear station operators to be attentive to the vulnerability of a facility’s systems to beyond-design basis events, Prof. Kondo said.
He said larger failures at other stations affected by the March 2011 Tohuku Earthquake and tsunami were prevented through diversification of protection systems.
Severe accidents did not occur at the Fukushima Daini, Onagawa and Tokai nuclear power stations, which were also affected by the earthquake and the tsunami.
This was because offsite power was not entirely lost. At Fukushima Daini one of four off-site power lines survived. At Onagawa, one of five lines survived and at Tokai, although all three off-site power lines were lost, two of three emergency diesel generators remained operational.
However, as a result of damage to off-site power facilities and transmission towers caused by the earthquake, off-site power was lost at all six units at Fukushima-Daiichi.
All emergency diesel generators at Fukushima-Daiichi – with the exception of one air-cooled diesel generator at Unit 6 – lost function because they were covered with water by the tsunami, the report says.
Preparing “diverse methods to respond to critical events” and making severe accident management resilient so it can even tolerate surprises is important for increasing nuclear station safety, Prof. Kondo said.
Such preparations include ensuring the availability of “multiple sets of portable backup safety equipment and a robust communications system between regulators and operators”, he said.
Prof. Kondo said increases in safety have to be taken seriously if the nuclear industry is going to continue to operate for the benefit of society.
