On the scaling of uncertainties in thermal hydraulic system codes

Abstract The present work addresses the scaling effect on safety margins and uncertainties for best estimate plus uncertainty (BEPU) methodologies. The results of an experiment from the OECD/NEA ROSA-2 project at the LSTF facility have been used. LSTF is a mock-up of a PWR reactor which follows a power-to-volume scaling approach. A validated RELAP5 model of the experiment has been upscaled to two different scales in order to assess the impact of the different uncertainty parameters. This process followed the scaling-up methodology (SCUP) developed at UPC. The comparison of the three calculations at different scales is presented as well as an uncertainty quantification following the GRS methodology for propagating uncertainties. The comparison of the propagation of the uncertainties at different scales has shown that the influence of the scale on the input parameters is negligible. On the other hand, the safety margins are slightly influenced by the scale of the reactor.

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