The Peach Bottom reactors are broadly similar to those in use at Fukushima. In fact, they are similar enough that the NRC even turned to this analysis to try to predict what might happen at the latter's during that accident. Much as what unfolded during the crisis in Japan, the computer modeling suggested that fuel in one of the two reactors on the Peach Bottom site would begin to melt as soon as nine hours after a loss of cooling water flow. Peach Bottom's Mark I containment would then fail roughly 20 hours after the earthquake if there was no restoration of cooling water. The breached reactor would then spew "16 percent of the core inventory"—"inventory" meaning cesium 137, along with 68 other radioactive isotopes in the hot nuclear fuel. The consequences of the release, the analysis concluded, "could be serious."
But the computer modeling only analyzed catastrophic failure at one reactor at each of these nuclear power plants, despite the fact that Peach Bottom and Surry each have two reactors on site. Multiple reactors might be expected to be similarly troubled by shared challenges, as seen during the Fukushima crisis. Nor did the modeling analyze what would happen if a powerful earthquake immediately destroyed safety equipment or ripped a hole in the structure containing the reactor itself.
The key weakness revealed by both the Fukushima plant and in the U.S. computer models is the reliability of backup electricity. The reactors at Fukushima had batteries big enough to power equipment, including monitoring instruments, for eight hours. U.S. reactors are required only to have two hours of such battery backup. "The NRC is currently revising the station blackout rule, and this effort could lead to change in battery coping times," the NRC's Burnell says. "The models show that when you have a station blackout where you still have batteries, there are steps that can be taken to go beyond what is considered the normal life of batteries." Engineers could extend battery life by recharging them and/or by shutting down all nonessential systems, for example.
The U.S. nuclear industry, for its part, is suggesting that it will voluntarily implement an approach it calls FLEX, which is meant to be a "diverse and flexible coping capability." Nuclear power plant operators would purchase and store portable equipment that could be used to provide additional means of cooling the reactor, a plan that could be in place as soon as 2015. "FLEX would provide multiple means of obtaining power and water needed to fulfill the key safety functions of core cooling, containment integrity and spent-fuel pool cooling that would preclude damage to nuclear fuel," explains Adrian Heymer, executive director of Fukushima regulatory response at NEI. That equipment list might include extra pumps, portable diesel generators for recharging batteries, additional battery packs and hoses as well as fuel and diesel-powered air compressors, among other things. They would keep the plant running for 72 hours. The similar work done to improve safety in the wake of the terrorist attacks in September 2001 "gives us a 10-year head start on dealing with unexpected events," argues NEI president Marvin Fertel, and FLEX builds on that approach.
Plus, new pressurized-water reactor designs currently under construction in Georgia, known as the AP-1000, incorporate so-called passive safety features, including enough water to cool a reactor for three days in the absence of any human action. "If this design had been used in Fukushima, we would not have a news story," argues nuclear engineer Aris Candris, CEO of Westinghouse, the company responsible for the new design. "The AP-1000 is immune to the loss of off-site power."