Breaking the Logic Loop to Complete the Probabilistic Risk Assessment.

摘要

A Level 1 Probabilistic Risk Assessment was performed for the N Reactor at the Hanford Site near Richland, Washington. This work was performed by the operating contractor for the US Department of Energy. As part of this analysis, fault trees were constructed for the various front-line and support systems necessary to respond to transient conditions. At the N Reactor, the normal operating system is also the initial accident mitigating system. Alternating current (ac) power is required for many components that must function to control and mitigate transient conditions. The reactor has two independent and redundant sources of ac power. The first source is the offsite ac power grid. The second source is produced onsite by a dedicated turbine generator, powered by reactor or oil-fired boiler steam. Some components that require steam-generated ac power play a role in generation of reactor or boiler steam. Thus, feedback mechanisms that create logic loops exist for various components and their power source. A large number of logic loops were broken so that the fault trees could be quantified. The advantage of the N Reactor Probabilistic Risk Assessment method for breaking these logic loops is that is provides a systematic and documentable approach that has not been described in Probabilistic Risk Assessment literature to date. 3 refs., 4 figs. (ERA citation 14:022249)