A group of nuclear power experts and former regulators from 11 nations, responding to Japan's nuclear disaster, is calling for "stress tests" on the world's reactors to determine their ability to withstand extreme earthquakes, flooding or other natural disasters that strike singly or in combination.
In a letter to the International Atomic Energy Agency in advance of the IAEA meeting later this month on the Fukushima Daiichi accident, the 17-member ad hoc group also urges that safety requirements for new nuclear plants be reviewed. The evaluations must ensure that backup cooling systems for reactors and spent fuel pools can operate for a long time in "blackout" conditions, where on-site and off-site power is cut off.
"We urge greater use of politically independent, multinational design reviews for future plants. ... The benefits of this approach have been demonstrated in the aircraft industry," the letter says.
"You have to move the safety envelope," said Roger Mattson, former leader of the U.S. task force that investigated the Three Mile Island nuclear accident in 1979, and an organizer of the group issuing the letter. "You have to take these severe accidents into account and do more to prevent the very low-probability events."
In addition to Mattson and Ashok Thadani, former director of the Nuclear Regulatory Commission office of research, the group's members include Sam Harbison, former chief inspector of the U.K. Nuclear Installations Inspectorate; Jukka Laaksonen of Finland, chairman of the Western European Nuclear Regulators' Association; M.R. Srinivasan, former chairman of the Atomic Energy Commission of India; and Victor Sidorenko, former deputy minister of nuclear power for the Soviet Union and Russia.
Peer reviews of developing nations
The letter's signatories direct part of their agenda toward nations whose nuclear programs are starting or accelerating. China, India and several Persian Gulf nations lead that list.
"Such countries must demonstrate their ability to uphold high international standards" on nuclear plant safety, security and non-proliferation, the letter signers say. The IAEA should consider a system of compulsory peer reviews of nuclear plant operators and national nuclear regulatory organizations, they add.
The letter also sets a demanding agenda for the U.S. nuclear industry.
Stress tests or safety audits of U.S. reactors should consider the hazards from severe natural disasters that are currently considered too unlikely to warrant mandatory regulation of the emergency equipment and procedures that would be called into play, the letter authors say.
Older nuclear plants require a particularly critical review to determine what "backfit" additions of safety measures are required, they say. If these improvements are not "reasonably achievable," then older plants should be allowed to operate for a limited grace period before being permanently shut down, the letter says.
As an example of a strategic backfit, Mattson cited France's requirement of backup generators that would be powered by excess steam from reactors during emergencies to deliver electricity to crucial pumps and monitoring instruments.
"Governments and regulators should exercise great care in permitting any extension of the operating life of the oldest nuclear power plants still in operation that were built to the easier safety standards," the letter says. "Continued operation of a few of the oldest plants for a few more years should not be allowed to jeopardize the continued operation of newer and safer plants in the longer term.
"Even if there are legal complications involved, we find it difficult to justify significant differences in general safety objectives for new and existing plants."
Proof needed of regulatory independence
Mattson said the group believes its recommendations will be considered by the IAEA ministerial meeting on the Japanese crisis that begins June 20 in Vienna.
An IAEA team reviewing the Japanese accident issued a preliminary report this week stating that Japan had underestimated the danger of tsunamis and had not provided adequate backup cooling systems at the Fukushima Daiichi nuclear complex.
"The operators were faced with a catastrophic, unprecedented emergency scenario with no power, reactor control or instrumentation," the report says. The tsunami also "severely affected communications systems both within and external to the site."
Emergency workers "had to work in darkness with almost no instrumentation and control systems," the report says.
The team said that Japan must ensure that "regulatory independence and clarity of roles are preserved in all circumstances," echoing criticism that close associations between Japan's nuclear regulators and industry officials had undermined strong safety oversight.
Mattson said he believes the IAEA meeting will look at the results from its inspection team and will probably set a schedule for further reviews and recommendations over this year. "My hope is that they will really open this question of international oversight," he said.
An initial inspection report on U.S. reactors by the Nuclear Regulatory Commission last month found that about one-third had some vulnerabilities to extreme emergencies, according to the NRC.
"Our inspectors found all the reactors would be kept safe even in the event their regular safety systems were affected by these events, although a few plants have to do a better job maintaining the necessary resources and procedures," said Eric Leeds, director of the NRC's Office of Nuclear Reactor Regulation.
Bracing for coincidental failures
Inspection reports disclosed that on one reactor, some door seals that were not hardened to withstand seismic shocks could fail in an earthquake, allowing water to enter rooms containing electrical equipment used to shut down the plant.
Another reactor had sump pumps and flooding detectors that were considered "non-safety related" and thus not hardened to withstand earthquakes, the NRC staff reported. Firefighting equipment at the reactor staged to respond to severe fires or explosions was not stored in hardened buildings because a severe fire and an earthquake "were not assumed to occur coincidentally."
A third plant had a single diesel-driven pump to provide emergency cooling water to a single reactor in case an earthquake cut off normal water flow. The pump could not have serviced both of the plant's reactors if they lost normal water supply simultaneously, the NRC staff said. The plant owner planned for a contractor to provide seawater for emergency cooling, but had no backup plan if an earthquake and tsunami blocked highways to the plant, the NRC said.
Mattson said the added safety measures likely to result from a more demanding look at nuclear plant vulnerabilities should not impose unreasonable costs on most plants. "I don't think it's breaking the bank," he said in an interview. "A higher sea wall [at the Fukushima Daiichi plant] wouldn't have broken the bank compared to what Japan will have to pay without the sea wall.
"Some of the older plants could be shut down, but some are beyond their design life. You shouldn't shut them down willy-nilly, like Germany did. But you ought to look at them really hard, with 'Fukushima eyes,' and see how comfortable you are."