NUREG-1150 risk assessment methodology and results

NUREG-1150 constitutes a full-scope reassessment of the risks to the public from several light water reactor plants with various containment types. Emphasis has been placed on determining the magnitude and character of the uncertainties, rather than focusing upon a point estimate. The risk-reduction potential of proposed plant modifications (backfits and procedural changes) has also been studied, and their costs and benefits have been evaluated. It has been found that the risks from internal events are generally lower than previously evaluated in the Reactor Safety Study (RSS). However, certain unresolved phenomenological issues cause the tops of the uncertainty bands to appear at levels that are comparable to or higher than the RSS point estimates. The issues that are important vary from plant to plant. Most of the postulated plant modifications do not appear to be cost-effective, although a few procedural changes are possible exceptions. Several reviews of this work are in progress, and a second iteration is being performed to include external events, incorporate new technical information, and address comments