EX-VESSEL BOILING EXPERIMENTS - LABORATORY-SCALE AND REACTOR-SCALE TESTING OF THE FLOODED CAVITY CONCEPT FOR IN-VESSEL CORE RETENTION .2. REACTOR-SCALE BOILING EXPERIMENTS OF THE FLOODED CAVITY CONCEPT FOR IN-VESSEL CORE RETENTION

This paper summarizes the results of a reactor-scale ex-vessel boiling experiment for assessing the flooded cavity design of the heavy water new production reactor. The simulated reactor vessel has a cylindrica l diameter of 3.7 m and a torispherical bottom head. Boiling outside t he reactor vessel was found to be subcooled nucleate boiling. The subc ooling mainly results from the gravity head, which in turn results fro m flooding the side of the reactor vessel. The boiling process exhibit s a cyclic pattern with four distinct phases: direct liquid-solid cont act. bubble nucleation and growth, coalescence, and vapor mass dispers ion. The results show that, under prototypic heat load and heat flux d istributions, the flooded cavity will be effective for in-vessel core retention in the heavy water new production reactor. The results also demonstrate that the heat dissipation requirement for in-vessel core r etention, for the central region of the lower head of an AP-600 advanc ed light water reactor, can be met with the flooded cavity design. (C) 1997 Elsevier Science S.A.