RELAP5 Assessment on CIRCE Decay Heat Removal Experiments

摘要

DHR experiments were carried out on the large scale LBE-cooled CIRCE facility at the ENEA/Brasimone center to verify the decay heat removal through heat exchangers immersed in the LBE pool under representative accidental conditions, and provide a valuable database for both CFD and system code assessment. The accidental conditions reproduced refer to a station blackout scenario, namely a protected loss of heat sink and loss of flow transient. In steady-state condition the forced circulation in the primary circuit is sustained by gas lift effect and the nominal power of the electrically heated section is removed through a bayonet-tube steam generator fed by water on the secondary side. The station blackout scenario is simulated by simultaneous switch-off of gas and water injection, while the heated section power is reduced to the decay level and the DHR system is activated by forced circulation of air on the secondary side of the heat exchanger. The results of the RELAP5 simulation for the most representative T-4 test conducted in CIRCE are presented in this paper in comparison with the experimental data. The RELAP5 code is able to reproduce very well the stationary conditions reached after about 7 hours and, with small uncertainties, the transition to natural convection conditions until the end of the transient phase lasting about 41 hours. The trend of temperature stratification in the LBE pool during both forced and natural circulation is rather well reproduced by the code. The largest uncertainty of the simulation concerns the air-cooled heat exchanger behavior, which showed large instability in its operation during the T-4 test.