Human Error Dynamic Simulation of Work as Performed – Modelling Procedure Deviations with Empirically Derived Failure Mechanisms

Abstract: HUNTER is an Idaho National Laboratory software tool developed to support dynamic human reliability analysis. The software performs Monte Carlo simulations of a virtual operator performing procedurally prescribed tasks within the context of a dynamic and coupled nuclear power plant model such that changes in the plant state impact what tasks the operator must perform and the operator’s actions impact the plant state. HUNTER supports a limited suite of scenarios with models containing procedures and corresponding human performance context parameters for a loss of feedwater and steam generator tube rupture scenario. The procedure models contain a single path of steps to mitigate the faults within the two scenarios. Failures occur from the dynamically calculated HEP value exceeding a random generated HEP value for any given task or if the elapsed time to complete a task exceeds the allowed time for that task. In the real world, Operators may error by proceeding along the wrong path and then exceed the allowed time to mitigate a fault as a consequence. To improve realism, HUNTER needs to be able to allow the virtual operator to incorrectly deviate along the wrong procedure path due to a diagnostic or understanding errors in addition to the existing HEP and time failures. Procedure deviations are errors of commission. These are quite challenging to model since there are theoretically infinite errors of commissions that could be made at any point in the simulation. Empirical data collected from a recently performed study evaluating computer-based procedures and failures to adhere to the prescribed procedure steps was used to derive failure mechanisms to realistically constrain the possible deviations to a manageable set that could be modelled within the HUNTER simulation. The process to analyze the empirical procedure adherence data and develop generalized forms of the empirically observed failure mechanisms are described along with their implementation within the HUNTER simulation. Future work aims to continue to validate these failure mechanisms outside of the specific context of the loss of feedwater and steam generator tube rupture contexts to understand their generalizability to other scenarios to more accurately model work as performed within nuclear process control.

Keywords: Dynamic Human Reliability Analysis, HUNTER, Human Error, Nuclear Power Plant Procedures, Computer-based Procedures

DOI: 10.54941/ahfe1004455

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