Recent results from treat tests on fuel, cladding and coolant motion

Abstract

Transient in-pile tests in the TREAT reactor are showing dispersive fuel movement and substantiate use of mechanistic modeling of such movements in Liquid Metal Fast Breeder Reactor (LMFBR) safety analyses. Test conditions are selected to mock-up the thermal histories calculated for hypothetical LMFBR accidents, and include use of previously irradiated fuel with various fuel structures. These test data are used in analyzing the consequences of LMFBR fuel failure under a range of hypothetical accident conditions and possible accident scenarios, as well as guiding descriptions of the extended fuel motion leading into the transition phase between the immediate post-accident configuration and the final stable, coolable configuration. Status of these experiments as of Spring 1974 was reviewed in three papers at the 1974 American Nuclear Society topical meeting on fast reactor safety: one on studies of transient overpower accidents (Rothman et al., 1974), one on loss-offlow accident studies directed toward behaviour of irradiated fuel (Deitrich et al., 1974), and one on loss-of-flow accident studies with fresh fuel using direct simulation of key axial LMFBR dimensions (Grolmes et aL, 1974). Since those reports, new data on cladding and fuel movement have been obtained from post-mortem examinations on those tests. Also, additional experiments have been run with the primary aims of clarifying the phenomena producing fuel motion, and of assessing the role of cladding motion as it might limit or otherwise affect fuel movement.