The evaluation of uncertainty constitutes the necessary supplement of Best Estimate (BE) calculations performed to understand accident scenarios in water cooled nuclear reactors. The needs come from the imperfection of computational tools on the one side and from the interest in using such tool lo get more precise evaluation of safety margins. In the present paper the approaches to uncertainty are outlined and the CIAU (Code with capabìlity ofinternal Assessment ofUncertainty) method proposed by the University of Pisa is described including ideas at the basis and results from applications. An activity in progress at the International Atomic Energy Agency (IAEA) is considered. Two approaches are distinguished that are characterized as “propagation of code input uncertainty” and “propagation of code output errors”. For both methods, the thermal-hydraulic code is at the centre of the process of uncertainty evaluation: in the former case the code itself is adopted to compute the error bands and to propagate the input errors, in the latter case the errors in code application to relevant measurements are used to derive the error bands. The CIAU method exploits the idea of the “status approach” for identifying the thermalhydraulic conditions of an accìdent in any Nuclear Power Plant (NPP). Errors in predicting such hydraulics status are derived from the comparison between predicted and measured quantities and, in the stage of the application of the method, are used to compute the uncertainty.

Approach and methods to evaluate the uncertainty in system thermalhydraulic calculations

D'AURIA, FRANCESCO SAVERIO
2004-01-01

Abstract

The evaluation of uncertainty constitutes the necessary supplement of Best Estimate (BE) calculations performed to understand accident scenarios in water cooled nuclear reactors. The needs come from the imperfection of computational tools on the one side and from the interest in using such tool lo get more precise evaluation of safety margins. In the present paper the approaches to uncertainty are outlined and the CIAU (Code with capabìlity ofinternal Assessment ofUncertainty) method proposed by the University of Pisa is described including ideas at the basis and results from applications. An activity in progress at the International Atomic Energy Agency (IAEA) is considered. Two approaches are distinguished that are characterized as “propagation of code input uncertainty” and “propagation of code output errors”. For both methods, the thermal-hydraulic code is at the centre of the process of uncertainty evaluation: in the former case the code itself is adopted to compute the error bands and to propagate the input errors, in the latter case the errors in code application to relevant measurements are used to derive the error bands. The CIAU method exploits the idea of the “status approach” for identifying the thermalhydraulic conditions of an accìdent in any Nuclear Power Plant (NPP). Errors in predicting such hydraulics status are derived from the comparison between predicted and measured quantities and, in the stage of the application of the method, are used to compute the uncertainty.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/86186
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