Experimental and Numerical Study of Liquid Metal Boiling in a System of Parallel Bundles under Natural Circulation Conditions

Numerical simulation of boiling of Na-K eutectic alloy (22% Na; 78% K) in a parallel channel system under natural circulation conditions is presented in this work. The calculations pertain to an experimental analysis conducted at the AR-1 facility of IPPE (Russia), analyzing the reactor core coolabilty under severe thermal conditions. The geometrical and operational characteristics reproduce those typical of Russian FBRs. A thermohydraulic code system based on a subchannel analysis code has been developed and adopted for the simulation. Comparisons show that the adopted numerical procedure is capable of reproducing the boiling phenomena inside the parallel bundle test section, correctly predicting the heat transfer conditions prior to and during the boiling. Experimental as well as computational results show the marked influence of the parallel channel interaction, evidenced by the appearance of severe flow oscillations. The results confirm that stable heat removal is provided throughout the entire transient.