On the scaling of uncertainties in thermal hydraulic system codes

Abstract

The present work addresses the scaling e ect 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 di erent scales in order to assess the impact of the di erent uncertainty parameters. This process followed the scaling-up methodology (SCUP) developed at UPC. The comparison of the three calculations at di erent 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 di erent 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.