The Generic Containment SB-LOCA accident simulation: Comparison of the parameter uncertainties and user-effect

Abstract

Uncertainties in safety assessment of the nuclear power plants using computer codes come from several sources: choice of computer code, user effect (a strong impact of user choices on the simulation’s outcome) and uncertainty of various physical parameters. The “Generic Containment” activity was performed in the frames of the EU-FP7 project SARNET2 to investigate the influence of user effect and computer code choice on the results on the nuclear power plant scale. During this activity, a Generic Containment nodalisation was developed and used for exercise by the participants applying various computer codes. Even though the model of the Generic Containment and the transient scenario were precisely and uniquely defined, considerably different results were obtained not only among different codes but also among participants using the same code, showing significant influence of the user effect.This paper present analysis, which is an extension of the “Generic Containment” benchmark and investigates the effect of input parameter’s uncertainties in comparison to the user effect. Calculations were performed using the computer code ASTEC, the uncertainty and sensitivity of the results were estimated using GRS method and tool SUSA. The results of the present analysis show, that while there are differences between the uncertainty bands of the parameters, in general the deviation bands caused by parameters’ uncertainty and the user effect are comparable and of the same order. The properties of concrete and the surface areas may have more influence on containment pressure than the user effect and choice of computer code as identified in the SARNET2 Generic Containment activity. It was identified and discussed that the definition of conservative parameters is complicated due to the fact that conservatism in terms of pressure level conflicts with conservatism regarding the gas mixture flammability.