Scaling Analysis of AP600 Long Term Cooling Performance

Abstract

Westinghouse’s AP600 thermohydraulic design, with passive safety features, poses new challenges to computer simulation and analyses, the design of experimental test facilities to represent it, and to the proper interpretation of the data from these facilities. The conventional approach of modeling the reactor thermohydraulic system as a closed, steady state, natural circulation loop from which non-dimensional groups of parameters can be derived and used in the design of integral tests, is limited and can not capture the abrupt time-varying open system nature of the new design. A rigorous and systematic, eight-step methodology has been developed to scale and interpret the results from three different integral test facilities, and to relate them to the full scale plant. In this paper, the aforementioned scaling methodology is applied to the analysis of the long term cooling phase of the AP600 behavior. This long term cooling phase, which appears independent of the initiating event, is divided for its analysis into two sub-phases. A first sub-phase dominated by the draining of the large In-Containment Refueling Water Storage Tank through the primary systems, and a second sub-phase characterized by the quasi-steady recirculation of coolant through the reactor vessel and the outside of the primary system. The analysis shows that with a few verifiable assumptions one can determine the key parameters and non-dimensional groups that govern the behavior in either of these sub-phases. One then uses these parameters and non-dimensional groups to evaluate the relevancy of existing test data.