Experimental results for long-term large-scale natural circulation in LWR containments after large and small LOCAs

For the first time, this paper presents and compares the experimental, long-term data of former HDR-containment blowdown experiments CONW and COND, tests V21.1 and V43, and the small-break, long-term blowdown experiments RBE and CON, tests T30.4 and T31.6 from Phases 1 and 2 of the HDR Safety Program in the large-scale HDR-Containment in Germany. The four experiments examined and evaluated in this paper cover the following changes in important parameters: (1) break size; (2) type of blowdown (subcooled water, steam); (3) break position with respect to its axial location in the containment; and (4) operation of Engineered Safety Features (ESF), such as internal spray. Results will be compared and conclusions will be drawn for: (1) vertical temperature distributions; (2) transverse temperature distributions; and (3) convective flows and global natural circulations. The review of the data base indicates the existence of large-scale global natural circulations which have the potential--depending on some conditions--to mitigate and homogenize non-uniform H2-concentration distributions