Politics and Policy 转自Physics Today US to act swiftly on reactor safety proposal A Nuclear Regulatory Commission task force has recommended that the emergency battery capacities of US nuclear reactors be upgraded. The proposal calls for a new minimum of eight hours of battery power to support cooling systems in the event that all AC power and diesel-generated power is lost. Jul 25, 2011 By David Kramer A Nuclear Regulatory Commission task force has recommended that the emergency battery capacities of US nuclear reactors be upgraded. The proposal calls for a new minimum of eight hours of battery power to support cooling systems in the event that all AC power and diesel-generated power is lost. The task force also urged that utilities be required to have ready the equipment and personnel needed to operate the plant’s cooling systems for at least three days after such an incident. According to the report, the initial eight-hour window would allow enough time for operators to deploy portable generating equipment in the event of a natural disaster—such as the March earthquake and tsunami that hit the Fukushima Daiichi reactors. The battery power should provide enough time for deployment of a second set of portable generators stored at the reactor sites. Those generators should be able to supply AC for an “extended coping period” of up to 72 hours, during which operators would bring in more durable generating equipment that is pre-staged at an offsite location. Current NRC regulations mandate four to eight hours of battery power, depending on the reactor, and do not include an extended coping period. Today’s requirements do not consider the possibility that AC power could be lost for many days, as occurred at Fukushima, the task force noted. The tsunami swamped and disabled the diesel generators that were designed to supply backup power, and batteries were depleted within hours. Without power, the coolant passing through the reactor cores and adjacent spent fuel pools was halted. The resulting partial meltdown of the reactor cores and the likely exposure of the spent fuel stored in pools was the worst nuclear accident since the 1986 Chernobyl disaster. The report noted that one generator at the plant remained operational and supplied cooling water to Fukushima’s other two reactors. At a public hearing on 19 July, NRC chairman Gregory Jaczko said the commissioners will consider the report and decide how to proceed within 90 days. Lessons learned Battery power capable of providing the necessary power for the first eight hours of a blackout could either be located 15 to 20 feet above the flood level specified in the plant’s license or be kept in watertight containers, the report said. Other specific changes to NRC regulations were recommended, such as “hardening” vents used in containment vessels of boiling water reactors, the type that were installed at Fukushima. Operators there were unable to open valves to relieve the pressure buildup inside the containment. That failure complicated their efforts and likely led to the buildup of hydrogen gas in the reactor buildings, which caused explosions in three of the units. The way that the hydrogen migrated outside the containment isn’t fully understood, the report noted. The task force also called for additional instrumentation for monitoring conditions in spent fuel pools and better methods for adding water to them. More broadly, the task force called for the NRC to order US reactor operators to reevaluate the risks posed to their plants by seismic events and flooding, and to order upgrades to the protections against those hazards, if necessary. Regarding the sequence of events that led to the partial core meltdowns at the Fukushima Daiichi plant following Japan’s March earthquake, the task force report said that scenario is “unlikely to occur” in the US, but that mitigation measures already implemented would “reduce the likelihood of core damage and radiological release” in case it were to happen. NRC should consider new regulations to address low-likelihood, high-consequence events that occurred at Fukushima, it said, and the commission should revamp its “patchwork of regulatory requirements and other safety initiatives” that has built up over time into a framework that is “logical, systematic, coherent, and better understood.” The Nuclear Energy Institute, the trade association of US nuclear plant operators, called for the NRC to consider input from the industry as it considers further regulatory action. “The task force report does not cite significant data from the Fukushima accident to support many of its recommendations,” said Tony Pietrangelo, NEI senior vice president. Pietrangelo added that the utilities have rushed to examine their existing procedures and have already taken steps to enhance safety.
标签: 核反应堆
