Total Risk Approach in Applying PRA to Criticality Safety

摘要

As nuclear industry continues marching from an expert-base support to more procedure-base support, it is important to revisit the total risk concept to criticality safety. A key objective of criticality safety is to minimize total criticality accident risk. The purpose of this paper is to assess key constituents of total risk concept pertaining to criticality safety from an operations support perspective and to suggest a risk-informed means of utilizing criticality safety resources for minimizing total risk. A PRA methodology was used to assist this assessment. The criticality accident history was assessed to provide a framework for our evaluation. In supporting operations, the work of criticality safety engineers ranges from knowing the scope and configurations of a proposed operation, performing criticality hazards assessment to derive effective controls, assisting in training operators, response to floor questions, surveillance to ensure implementation of criticality controls, and response to criticality mishaps. In a compliance environment, the resource of criticality safety engineers is increasingly being directed towards tedious documentation effort to meet some regulatory requirements to the effect of weakening the floor support for criticality safety. By applying a fault tree model to identify the major contributors of criticality accidents, a total risk picture is obtained to address relative merits of various actions. Overall, human failure is the key culprit in causing criticality accidents. Factors such as failure to follow procedures, lacks of training, lack of expert support at the floor level etc. are main contributors.