NAS panel criticizes basics of U.S. nuclear safety approach

Washington, D.C. – Is the conventional approach to nuclear safety in the U.S. – and most of the world – fundamentally flawed? That’s the clear implication of a recent National Academy Sciences report on the U.S. response to the 2011 catastrophe at Fukushima. Although the report has not gotten much attention in the U.S. media, it represents a serious challenge to how the industry and its regulators think about reactor safety.

The underpinning of the U.S. regulation of nuclear power plant safety, going back more than 50 years, is preventing “design-basis” accidents. That is, regulators attempt to ascertain that plants are built to withstand specific events that engineers and regulators say are more likely given the basics of the design of the plants. As the NAS report – Lessons Learned from the Fukushima Nuclear Accident for Improving the Safety of U.S. Nuclear Plants – defines the terms, “A ‘design-basis event’ is a postulated event that a nuclear plant system, including its structures and components, must be designed and constructed to withstand without a loss of functions necessary to protect public health and safety. An event that is ‘beyond-design-basis’ has characteristics that could challenge the design of plant structures and components and lead to a loss of critical safety functions. The Great East Japan Earthquake and tsunami were beyond design-basis events.”

As the NAS report makes clear, the other major nuclear accidents that preceded Fukushima – Three Miles Island in 1979 and Chernobyl in 1986 – were also beyond the design basis analysis for the plants involved. They also had effects that extended beyond the footprint of the nuclear installation, as did Fukushima. “A design-basis accident is a stylized accident, for example a loss-of-coolant accident or transient overpower accident, that is required (by regulation) to be considered in a reactor system’s design,” says the academy’s report. “The Fukushima Daiichi accident was a beyond-design-basis accident. Other major nuclear accidents (Three Mile Island in 1979 and Chernobyl in 1986) are also considered to be beyond-design-basis accidents.”

The academy report finds, “Four decades of analysis and operating experience have demonstrated that nuclear plant core-damage risks are dominated by beyond-design-basis accidents. Such accidents can arise, for example, from multiple human and equipment failures, violations of operational protocols, and extreme external events. Current approaches for regulating nuclear plant safety, which have been traditionally based on deterministic concepts such as the design-basis accident, are clearly inadequate for preventing core-melt accidents and mitigating their consequences.”

The NAS panel calls on the U.S. to incorporate “modern risk concepts” into its regulatory regime. The report says, “The committee uses the term ‘modern risk concepts’ to mean risk that is defined in terms of the risk triplet (What can go wrong? How likely is that to happen? What are the consequences if it does happen?) and subject to the limitations for quantitative analyses….”

The report also says the U.S. needs to take a closer look at emergency preparedness for a major accident, faulting Japan for an inadequate emergency response (which is still unfolding). While the NAS panel did not look into preparedness in depth, the panel advised that the Fukushima catastrophe “raises the question of whether a severe nuclear accident such as occurred at the Fukushima Daiichi plant would challenge U.S. emergency response capabilities because of its severity, duration, and association with a regional-scale natural disaster.”

The U.S. industry’s response to the NAS was predictably anodyne. In a press release, the Nuclear Energy Institute said the NAS report “is notable for the extent to which it affirms the culture of safety adhered to by the U.S. nuclear industry.” Anthony Pietrangelo, NEI’s chief nuclear officer, said, “The U.S. nuclear energy industry began taking steps within days of the Fukushima Daiichi accident to ensure that U.S. reactors could respond to events that may challenge safe operation of the facilities,” citing the industry’s “FLEX” program, adopted to offer a way to cope with an accident such as occurred in Japan.

I suspect that within the NEI, the NRC, and the licensees and vendors, the report is getting considerably more serious scrutiny than NEI’s public patting itself on the back.