Gesellschaft fuer Anlagen- and Reaktorsicherheit (GRS) has been performing a probabilistic analysis for a boiling water reactor (BWR) during low-power and shut-down (LP and SD) states. The reference plant is Gundremmingen NPP with a twin unit of 1344-MW electrical power each. The LP and SD study is in the final phase. This paper discusses some problems that were observed within the study, especially concerning human reliability assessment (HRA) and data issues. Some approaches will be presented to overcome some of the limitations in modeling human reliability in order to achieve a more realistic assessment of risk in shutdown states. The approaches were applied on selected scenarios. The main conclusions that have to be considered for a more realistic assessment of shutdown states include: methodological improvements concerning the event- and fault-tree approach are necessary to consider the various conditions under which human interactions have to be performed during LP and SD; current HRA-methods that are designed to assess human actions during design-base accidents and accident management conditions are not appropriate for all types of actions that have to be performed during LP and SD: methodological improvements are necessary, especially concerning the inclusion of administrative aspects, the variety of the types of actions, the recovery potential of operators, and the modeling of diagnosis     «

Gesellschaft fuer Anlagen- and Reaktorsicherheit (GRS) has been performing a probabilistic analysis for a boiling water reactor (BWR) during low-power and shut-down (LP and SD) states. The reference plant is Gundremmingen NPP with a twin unit of 1344-MW electrical power each. The LP and SD study is in the final phase. This paper discusses some problems that were observed within the study, especially concerning human reliability assessment (HRA) and data issues. Some approaches will be presented...     »