Chugging boiling in low-void SFR core: new phenomenology of unprotected loss of flow

Calculational analysis of the unprotected loss of flow (ULOF) accident in a Generation-IV SFR, featuring a low-void core design, shows that the chugging sodium boiling regime in the core could last for several hundred seconds during the accident. While in the case of the traditional positive-void SFR core the sodium boiling onset is almost immediately followed by the power run-away, fuel bundle overheating, melting and relocation (i.e. severe accident), the chugging boiling regime in the low-void SFR core could allow avoiding the power runaway and avoiding or at least significantly postponing the cladding overheating and melting caused by the permanent dryout. The low-void core design therefore could be classified as a new safety measure acting as a level of defence preventing the severe accidents. The knowledge in the area of the chugging regime of the sodium boiling is very limited and very few corresponding experiments were performed. The paper discusses possible phenomenology of the chugging boiling in the low-void SFR core and makes proposal for the new test facility. The goals of the new experiment are to better understand the conditions under which the chugging boiling regime establishes in the specific geometry of the low-void SFR core channel as well as the conditions under which the pressure pulses caused by the abrupt condensation can occur, and validate the system code for these conditions.