Results and implications of the EBR-II inherent safety demonstration tests

On April 3, 1986 two milestone tests were conducted in EBR-II. The first test was a loss of flow without scram and the second was a loss of heat sink without scram. Both tests were initiated from 100% power and in both tests the reactor was shut down passively-by natural processes, principally thermal expansion-without automatic scram, operator intervention, or the help of special in-core devices. The temperature transients during the tests were mild, as predicted, and there was no damage to the core or reactor plant structures. In a general sense, therefore, the tests plus supporting analysis demonstrated the feasibility of inherent passive shutdown for undercooling accidents in metal-fueled LMRs. The results provide a technical basis for future experiments in EBR-II to demonstrate inherent safety for transient overpower accidents and to provide additional data for validation of computer codes used for design and safety analysis of inherently safe reactor plants