SAS4A analysis of abrupt loss of flow without scram in metallic fueled fast reactors

摘要

The energetics potential of severe accidents is investigated for a large sodium cooled, metallic-fueled fast reactor using the SAS4A accident analysis code. The accident initiator considered is an abrupt loss of flow with failure to scram. Extensive analysis of the response of metallic fueled reactors to double fault initiators such as loss of flow, loss of heat sink, or transient overpower with failure to scram shows that the reactors passively adjust their power to match the available heat rejection capability without boiling coolant or melting fuel. The analysis considered here assumes some extremely unlikely additional contribution to the accident such as the failure of the flow-coastdown mechanism. The reactivity insertion rate due to coolant voiding and the low melting point of metallic fuel cause fuel to disperse within intact cladding prior to cladding failure. Negative reactivity feedback from this in-pin fuel motion counters the positive reactivity insertion and prevents a rapid and large release of energy. The SAS4A analysis shows that extensive core melting and disruption can be expected, but that the energy release will not be large enough to threaten rupture of the reactor vessel. Metallic fuel acts as an additional safety device which acts to counter large or rapid reactivity insertions. (ERA citation 19:033142)