A dynamic treatment of common cause failure in seismic events

Internal event probabilistic risk assessment (PRA) and seismic probabilistic risk assessment (SPRA) conventionally employ static event trees. Seismic events are dynamic by nature and may involve the need for effective human response within challenging time windows. In situations in which human reliability or the relative timing of events can be significantly affected by the current (or often past) conditions of the plant, dynamic PRA (DPRA) methods are more capable of assessing risk due to their capability for accounting for such effects explicitly. The dynamic characteristics of a hypothetical seismic scenario in a pressurized water reactor involving loss of both auxiliary feed-water trains and the high pressure injection system due to common cause failures are investigated. The time-dependent recovery actions of plant personnel to shut down the plant without severe core damage are examined including the implementation of FLEX equipment stored on-site. The potential for delay in recovery actions resulting from the stochastic occurrence of aftershock is modeled.