Post-Test Analysis of the Experiment 5.2c- Total Loss of Feedwater at the BETHSY Test Facility

In the framework of the external validation of the thermohydraulic code ATHLET Mod 1.1 Cycle D, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the french integral test facility BETHSY.
The BETHSY experiment 5.2c investigates the accident procedures in case of a total loss of feedwater at the steam generator secondary side, [3]. In such an accident the emergency cooling of the reactor core with primary bleed and feed, the behaviour of the steam generators in case of dry out and the long time behaviour of the test facility are special subjects of interest. During the experiment the high pressure injection system, the hydroaccumulators and the low pressure injection system were available.
The evaluation of the calculated results shows, that all main phenomena can be calculated in a good quality compared with the experiment. Resulting from various calculations it should be noticed that the quality of the results strongly depends on the modelling of the heat losses of the facility, which were partly compensated by the trace heating. This trace heating was changed several times in the experiment to compensate the changing heat losses. The exact modelling of the resulting heat losses has a strong influence on the course of the whole transient. In this test the unsufficient modelling of the resulting heat losses may be the reason for deviations of the calculated transient from the observed transient.
The results show, that the safety relevant statement of the experiment could be reproduced by the code ATHLET.