Scaling of the small-scale thermal-hydraulic transient to the real nuclear power plant

This paper provides a scaling methodology that was applied for scaling of the BETHSY integral test facility to the real nuclear power plant (NPP). The similarity of physical phenomena between the BETHSY experimental facility and the scaled-up model (representation of the real NPP) was analyzed on the small-break loss-of-coolant accident (SBLOCA) scenario. A comprehensive numerical analysis using the RELAP5 thermal-hydraulic code was performed to evaluate the optimal scaling-up of the BETHSY facility to the real NPP. In order to investigate the phenomenological scaling-up basis, two enlarged RELAP5 input models were constructed, differing in scaling criteria for the primary cooling system: proportional volume scaling and scaling based on the Froude number. A better agreement with the physical phenomena of the SBLOCA experiment was achieved in the case of proportional volume scaling. In addition, scaling of heat structures was also analyzed. It was shown that the best predictions of the transient phenomena were obtained when the heat structures were scaled according to the tensile stress criterion.