Procedure for the analysis of errors of commission during non-power modes of nuclear power plant operation

The continued, historical occurrence of human interactions which place nuclear power plants in a condition of potentially heightened risk is of increasing interest to regulators, utility management, and industry observers alike. These Errors of Commission (EOCs), as they are often called, lead to a variety of questions such as: ‘Can the event lead to a potentially dangerous condition such as core damage? By what failure mechanisms? With what frequency? What defences does the plant have to mitigate the event? Are these actions in the Probabilistic Risk Assessment (PRA) model of the plant?’. EOCs are often excluded from the bounds of a typical PRA model, yet they have the potential for being significant contributors to risk. This paper is the second of two describing procedures for the analysis of the potential for significant errors of commission. The first paper addressed operations at power while this paper describes the procedure for non-power operations. Each procedure describes a method for identifying the opportunities for error, identifying failures modes of functions, systems, or components that could arise from such errors (referred to in this paper as error expressions), and the identification of the most significant of these EOCs based on consideration of consequences, recovery potential, and likelihood.