The US Nuclear Regulatory Commission (NRC) has said the impact of a large aircraft on a Westinghouse AP1000 reactor would not jeopardise nuclear safety.
The AP1000 received design certification in 2005, before the NRC brought in a rule on aircraft impact. The company thus redesigned the AP1000 shield building and submitted their justification of the design.
One effect of strengthened buildings was to reduce passive heat removal airflow, NRC noted, but this effect was acceptable while affording greater protection from external impact, according to World Nuclear News.
The eventual conclusion of the NRC's Advisory Committee on Reactor Safeguards (ACRS) on 19 January was: "Analyses show that the containment remains intact following the impact of a large commercial aircraft. The reactor core remains cooled, and spent fuel integrity is maintained."
The US NRC said the AP1000 presents "a small target with a reduced set of safety-related structures, systems and components." The ACRS noted that passive systems provide core cooling, no active equipment is required for fuel pond cooling and at least one backup water source is always available.
Separately from penetration and fire, the 'shock loadings' on the power plant buildings from aircraft impact were shown to be less than potential earthquakes already accounted for during normal design analysis.
One feature of the AP1000 containment is an opening in the roof for passive heat removal, surrounded by a water storage tank. A concern had been the potential for "significant aircraft impact debris" to pass through the gap and hit the steel containment vessel.
The ACRS actually concluded that "no significant debris would impact the containment vessel" but a conservative analysis by Westinghouse showed that the vessel could be dented but not penetrated.
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