Towards the Development of Shutdown Emergency Operating Procedures for Power Nuclear Reactors

Virtually all operating nuclear plants have a well-developed suite of accident procedures which can be used in the event of an accident while the unit is at power. The procedures guide the operators through optimal recovery strategies to place the plant in a safe stable shutdown state. These procedures cater for design basis accidents as well as certain accidents which are not considered design basis accidents, but may be included in the plant’s licensing basis. Generally procedures used for accidents during power operation can also be used for initiating accidents which occur while the unit is shutdown while the core is cooled with steam generators. When the unit is in lower shutdown states and the residual heat removal system is in service, however, the procedure scope becomes somewhat constrained. With the reactor coolant system in an open or closed configuration, the state/configuration specific procedure guidance provided by Emergency Operating Procedures for power operation is often deficient. There is ample literature on developing emergency operating procedures for plant states where the energy (as a function of pressure and temperature) in reactor coolant system is high. However, much fewer sources of literature exist for shutdown plant states when the energy in the reactor coolant system is lower. This paper attempts to bridge this gap by proposing a framework for the development of shutdown emergency operating procedures using the plant specific Probabilistic Safety Assessment (PSA) model. The paper provides an initial framework for the development of Shutdown Emergency Operating Procedures (SD-EOPs) using the PSA. It describes the process of identifying event sequences for which restoration strategies are required from the PSA and briefly explains the analysis that should be performed to demonstrate that restoration strategies are successful in mitigating event consequences.