The author describes the methodology adopted to model the operator actions in the probabilistic safety study of the Magnox nuclear power plant situated at Latina, Italy. The methodology takes into account two distinctive features of plant operation: the intrinsic slowness of the thermal transient, and a low degree of safety-feature automation. The methodology adopted for the study was basically consistent with the guidelines of the NUREG CR/1278. The operator actions were modeled by subdividing them into two phases; diagnosis and action, each of them with the possibility of recovery. The quantification was performed under different assumptions of stress level, degree of dependence, and presence of oral instructions, according to the necessity of diagnosis and to whether the actions have to be carried out locally or in the control room.
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