Task force reports on US plant safety

While already considered safe, US nuclear power plants should improve their preparedness for major accidents and ensure that back-up power sources would be available, a task force has recommended to the country's regulator. The group also suggested ways of improving the USA's nuclear safety framework. 

In the days following the accident at the Fukushima Daiichi nuclear power plant in Japan, the US Nuclear Regulatory Commission (NRC) called for a senior-level agency task force to conduct "a methodical and systematic review" of the commission's processes and regulations.

The Near-Term Task Force has now submitted a report to the NRC detailing its findings and giving recommendations on how both plant safety and the regulatory system can be improved. The near-term review will be followed by a longer term review with a report with further recommendations within six months.

The seven-member Task Force noted that "an accident involving core damage and uncontrolled release of radioactive material to the environment, even one without significant health consequences, is inherently unacceptable." However, it cautioned that "there likely will be more than 100 nuclear power plants operating throughout the United States for decades to come," and developed its recommendations "in full recognition of this environment."

"The current regulatory approach, and more importantly, the resultant plant capabilities allow the Task Force to conclude that a sequence of events like the Fukushima accident is unlikely to occur in the United States and some appropriate mitigation measures have been implemented, reducing the likelihood of core damage and radiological releases," the report said. "Therefore, continued operation and continued licensing activities do not pose an imminent risk to public health and safety."

The Task Force said that the NRC's current approach to regulation includes requirements for protection and mitigation of design-basis events, requirements for some beyond-design-basis events through regulations, and voluntary industry initiatives to address severe accident issues. "This regulatory approach, established and supplemented piece-by-piece over the decades, has addressed many safety concerns and issues, using the best information and techniques available at the time," the report said. "The result is a patchwork of regulatory requirements and other safety initiatives, all important, but not given equivalent consideration and treatment by licensees or during NRC technical review and inspection." The Task Force said that improving the NRC's regulatory framework is "an appropriate, realistic and achievable goal."

The report concludes that "a more balanced application of the commission's defence-in-depth philosophy using risk insights would provide an enhanced regulatory framework that is logical, systematic, coherent, and better understood. Such a framework would support appropriate requirements for increased capability to address events of low likelihood and high consequence, thus significantly enhancing safety."

The Task Force developed a comprehensive set of 12 recommendations for improving nuclear power plant safety, including that plant operators "re-evaluate and upgrade as necessary the design-basis seismic and flooding protection of structures, systems and components for each operating reactor" every ten years.

The group also recommends that the NRC strengthen plant blackout mitigation capability at all operating and new reactors for design-basis and beyond-design-basis natural external events. It suggests that plants should be required to cope without offsite or onsite AC power for at least eight hours and that measures are in place so that the reactor core and used fuel pools can be kept cool for at least 72 hours. Plant emergency plans should address prolonged blackouts and events in multiple reactors, the report said. The Task Force also recommends additional instrumentation and seismically-protected systems to provide additional cooling water to used fuel pools if necessary. In additional, at least one system of electrical power should be available at all times to operate used fuel pool instrumentation and pumps.

It also suggests that reliable hardened vent designs are required in boiling water reactor units with Mark-I or Mark-II containments, like those at Fukushima Daiichi. The longer term review should also consider hydrogen control and mitigation within the containment and other buildings. The NRC should also "evaluate potential enhancements to the capability to prevent or mitigate seismically induced fires and floods."

Charles Miller, who led the review team, commented: "Our recommendations are grouped into four areas beyond the overarching suggestion to clarify the agency's regulatory framework." He added, "We looked at ensuring protection, enhancing accident mitigation, strengthening emergency preparedness and improving the efficiency of NRC programs."

While welcoming the Task Force's finding that the country's nuclear power plants are safe, US industry body the Nuclear Energy Institute (NEI) called on the NRC not to rely solely on the group's report to form regulatory policy. NEI's senior vice president and chief nuclear officer Tony Pietrangelo said: "The task force report does not cite significant data from the Fukushima accident to support many of its recommendations. Given the mammoth challenge it faced in gathering and evaluating the still-incomplete information from Japan, the agency should seek broader engagement with stakeholders on the task force report to ensure that its decisions are informed by the best information possible."

He added, "The NRC has always supplemented regulatory requirements based on operating experience and significant events. The industry expects this NRC practice will continue with a focus on those aspects that are most important to plant safety."

Researched and written

by World Nuclear News