Feasibility Study on Integratin of Operator Modelling in DICE^TM

PSA (Probabilistic Safety Assessment) using ETs (Event Trees) and FTs (Fault Trees) has contributed to enhancing the safety of nuclear facilities. Although PSA has been evaluating the safety of nuclear facilities for a long time, the necessity to introduce a method to complement the existing approaches is increasing due to the complexity of risk assessment such as wide-range analysis, long-term evaluation, mobile devices, and so on. To facilitate these limitations, Integrated Deterministic Probabilistic Safety Assessment (IDPSA) which can facilitate contextual evaluation with sensitivity and uncertainty analysis has been proposed. DICE (Dynamic Integrated Consequence Evaluation), a dynamic reliability analysis tool using DDET, was developed as a supporting tool for the conventional PSA. The DICE consists of a physics module, a diagnostic module, a reliability module, and a scheduler that controls the three modules. DICE has two simulation modes called single-branch mode and multi-branch mode, depending on the purpose of analysis.

The diagnosis module reflects the operator's tasks in DICE. The diagnosis module including the operator model has an important role in temporal dependence on accident scenarios and various accident propagation can be seen. Although the same accident scenario occurs, there is a possibility that it will proceed to a different scenario due to the results of the operator model. Through this, unknown scenarios can be explored and it can supplement conventional PSA.

The operator model determines the success or failure of the operator task and, upon success, also determines operator action time. This model maintains consistency with the HRA(Human Reliability Analysis) applied to the existing PSA, so provides the same result, which is human error probability, while calculating operator action time. The operator model randomly calculates success or failure and operator action time according to a specific distribution set for each simulation. accident scenario variability can be affected by providing time variability for the operator action time. The operator model can also be developed with other HRA methods and is currently developed based on SPAR-H.

Keywords: Nuclear Power Plant, DICE^TM, IDPSA, Operator Model, Exploring Scenario, SPAR-H

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