"The Nuclear Regulatory Commission should consider requiring nuclear power plants to analyze their vulnerability to natural hazards like earthquakes by using the same advanced tools that the industry uses to understand the risks from mechanical accidents, a new report from the Government Accountability Office argues."
"A string of natural disasters has recently drawn attention to nuclear safety and natural disasters, including the Fukushima Daiichi quake and tsunami in March 2011, tornado damage near the Tennessee Valley Authority’s Browns Ferry complex in April 2011, the Missouri River flooding that nearly inundated two reactors in Nebraska last summer and the quake near Mineral, Va., last August.
Almost all of the plants now running were licensed in the 1970s or 1980s, when safety was analyzed on what is known as a 'deterministic' basis. That means drawing up a list of potential malfunctions and adding enough hardware to prevent them, including redundant systems that would tolerate multiple failures.
But more recently, regulators have been pushing the industry to embrace a technique known as 'probabilistic risk assessment.' This involves drawing up a chart of a potential sequence of events and calculating the probability of each step in the sequence. That allows engineers to rank the likelihood of each accident and the components most likely to fail. The commission then focuses on the higher-risk accidents and components, a technique it calls 'risk-informed regulation.'"