The normal base-line PSA mainly serves the purpose of determining if an initiating event can cause a radioactive release or not, and which function barriers that need to fail for such a catastrophic consequence to occur. This is typically achieved by determining how the accident sequences would look like for each initiator in combination with assigning end states to each sequence which either represent core/fuel damage (CD/FD) or not. With this mindset, the PSA has a focus on the radiological safety aspects of the nuclear facility in question and PSA model can be used in several various applications focusing on reducing, or balancing, the risk of a radiological release. While this is certainly of interest to both the operator of the facility and the regulatory body, it may not provide the desired level of detail to be used in planning how the facility should be configured in situations where multiple options are available. The typical example for such a scenario relates to planning how the facility will be configured during the refueling outage. The base-line PSA will be able to provide risk insights from a core/fuel damage perspective, and the Technical Specifications will provide boundaries on minimum capacities for the system functions, again from a safety point of view.

If one would like to analyze not only the risk of the severe consequences as defined in the base-line PSA, but also taking into account consequences that would have an impact on the facility’s ability to produce power in the future one also need to look at those sequences that do not give rise to core/fuel damage (i.e. radiological release), as they most likely include plant states which might limit, or delay, future operation in different degrees. It shall be recognized that this will be the vast majority of all possible sequences.
This type of extended application of the base-line PSA will require a significant re-visit of underlaying analysis and refinement of the PSA model as such, including 1) definition of the economic consequences; 2) revisit of initiating event analysis, especially looking at initiators that have been screened out; 3) grouping of sequences that do not give rise to radiological release into plant states for which defined economic consequences can be assigned; 4) revisit of system requirements for credited systems; 5) identification of system functions that have not been credited in the base-line PSA but could be of importance from an economic perspective; and 6) refinement of the PSA model itself.

The presentation for this abstract will provide insights from a real case for which the PSA for the refueling outage in particular is further developed so that economic consequences can also be considered.