Issues of Risk Taking Behaviour in SAMG Performance

Severe accident management is the series of actions designed to mitigate the consequences of severe fuel damage in either the core or the spent fuel pool. In IAEA terminology, it is the series of actions that is designed (abbreviated): As such accidents are outside the plant design basis and the accident evolution cannot be predicted well, no firm operator instructions can be given to mitigate the accident. Hence, such instructions take the form of guidance rather than procedures, i.e. the instructions need not to be executed verbatim: there is space for additional deliberation and deviating decision-making. The usual term hence is ‘severe accident management guidance/guidelines’, well known under its acronym SAMG. Inherent then in the execution of these guidelines is an element of uncertainty: the knowledge needed to decide on SAMG actions is incomplete. Consequently, each decision is characterised by taking a certain risk. The paper indicates where the major sources of the uncertainty are and, hence, where the risks associated with the decisions lie. These can be grouped in various parts: imperfect knowledge of the status of the plant and the accident evolution, imperfect knowledge about the availability and capability of the means needed to mitigate the accident, and imperfect human behaviour under the stress of the accident, resulting in errors of commission and/or omission. Examples will be given of major uncertainty areas in SAMG and some remedies will be suggested to enhance and strengthen the SAMG.