Visual in-pile fuel disruption experiments. [LMFBR]

In a loss-of-flow (LOF) accident in a liquid-metal fast breeder reactor, the mode of disruption of fuel may determine the probability of a subsequent energetic excursion. To investigate these phenomena, in pile disruption of fission-heated irradiated fuel pellets was recorded by high-speed cinematography. Instead of fuel frothing or dust cloud breakup (as used in the SAS code) massive and very rapid fuel swelling, not predicted by analytical models, occurred. These tests support massive fuel swelling as the initial mode of fuel disruption in an LOF accident. 10 refs.