With post-Sept. 11 security concerns seen as a priority issue, the U.S. Nuclear Regulatory Commission (NRC) has unveiled a proposal that would require each applicant for a new nuclear reactor design to assess how the design, to the extent practicable, can have “greater built-in protections” to “avoid or mitigate the effects” of a large commercial aircraft impact, making the plants even more resistant to an attack.

The commission emphasized that seeking security assessments and examining how designs can be improved is consistent with the traditional approach the NRC has taken to so-called “beyond design basis events.” These are events with conditions exceeding the stresses imposed by the “design basis event” conditions, which require plants to be brought to a safe shutdown, the NRC explained. Design basis event conditions include large pipe breaks, fires, earthquakes, hurricanes, tornados and floods. “Assessing a new reactor design in the early stages can enable modifications or additional features to reduce the need for human intervention in the event of an airplane crash,” the commission said.

The Sept. 11 attacks using hijacked planes forced the nuclear power industry, as well as anti-nuclear activists, to take a good look at the vulnerability of nuclear plants. However, making a nuclear reactor so-called “plane-proof” could choke off the recent momentum and support for more nuclear generation. According to a Cambridge Energy Research Associates study earlier this month, “several dozen reactors” in the United States are in various stages of proposal development, which is big news in a country where no new reactor has been ordered in 28 years. In addition, 48 current U.S. reactors have been granted 20-year life extensions, with the remaining 56 “likely” to be granted extensions, the report noted.

The NRC said it will seek comments from the public, the nuclear industry and the technical community on the proposal. The proposed rule, which will replace an NRC staff proposal, will be available for comment later in 2007.

“This is the most recent step in a broad, proactive effort to improve the security of reactors initiated by the NRC after Sept. 11, 2001,” said Dale Klein, NRC chairman. “We need more technical analysis to understand how to address this. At the end of the road there may not be any changes necessary, but there also may be additional things that can be done.”

In 1985 the NRC said it expected reactor designers to build in more safety features to cope with beyond design basis severe accidents as reactor designs advanced. However, the commission did not require specific features, leaving that to plant designers. In the subsequent decades, reactor designs submitted to and approved by the NRC have achieved substantial safety improvements, the commission added.

The proposed rule, if adopted, will affect new applicants for reactor design certification and applicants for a combined license that does not reference a certified design. It would require applicants to describe how the design, to the extent practicable, can avoid or mitigate the effects of an aircraft crash with reduced reliance on actions by reactor operators. That approach, the commission found, “allows the designers to evaluate potential competing technical factors, such as the response to earthquakes and passive safety systems, while at the same time addressing aircraft impacts.” The commission said the assessments should look at areas such as core cooling capability, containment integrity and spent fuel pool integrity.

“This proposal gives us the chance to assess and make practicable changes to new reactor designs early in the design process,” Klein said, adding that even for plants already certified it would be “in the interest of both the designers and their clients to adopt these changes at the design stage.”

The agency in January approved a final rule enhancing security regulations governing the design basis threat (DBT) against which nuclear power plants must be able to defend with high assurance using their own capabilities. The NRC decided not to include large commercial aircraft in the DBT because the weaponry needed to defend against such a threat, surface-to-air missiles or fighter aircraft, cannot be possessed by the private security forces that protect commercial nuclear plants. The responsibility for such a threat belongs with the U.S. government, which has taken numerous steps to prevent terrorist use of large commercial aircraft since 9-11.

In another step to address aircraft impact, building on a directive put in place in February 2002, the agency told reactor operators to develop strategies to mitigate the impact of large fires and explosions potentially caused by an aircraft impact. Comments on a proposed rule codifying that step for both existing and new reactors are being examined by the NRC staff in preparation for a final rule for commission consideration.

In addition to design and mitigative measures for reactors, the NRC said it also works closely with other federal agencies such as the North American Aerospace Defense Command (NORAD), the Federal Aviation Administration and the intelligence community to provide layered protection. The NRC has an agreement with NORAD that enables reactor operators to learn rapidly of imminent aviation threats and swiftly place the reactor in a safe state.

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