NRC Proposes Plane Crash Security Assessments to Nuclear Reactor Design Certification Requirements
May 4, 2007 // Published as a news service by IHS
The U.S. Nuclear Regulatory Commission (NRC) unveiled the third in a series of major steps to enhance the post-Sept. 11 security of nuclear power plants.
The agency proposal would require each applicant for a new 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 them even more resistant to an attack.
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 will require applicants to describe how the design can avoid or mitigate the effects of an aircraft crash with reduced reliance on actions by reactor operators.
The NRC said the assessments should look at areas such as:
That approach, the NRC 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."
NRC Chairman Dale Klein said 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."
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. The third major step taken was the proposal on security assessments for new reactor designs.
Design Basis Events and Threats
The NRC 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.
Design basis event conditions include:
- Large pipe breaks.
- Fires.
- Earthquakes.
- Hurricanes.
- Tornados.
- 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.
In January 2007 the agency 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 Sept. 11.
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, it 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 NRC will seek comment from the public, the nuclear industry and the technical community on the proposal, which will replace an NRC staff proposal, later in 2007.
Source: U.S. Nuclear Regulatory Commission (NRC).