Report on Fuel Fragmentation, Relocation and Dispersal (FFRD)

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Since the time of the first LOCA experiments, which were largely conducted with fresh fuel, changes in the fuel design, the introduction of new cladding materials and in particular the move to high burnup have generated a need to re-examine the LOCA safety criteria and to verify their continued validity. As part of international efforts to this end, the OECD Halden Reactor Project programme implemented a LOCA test series. 

After these Halden tests, the Nuclear Regulatory Commission of the United States (U.S.NRC) initiated the Studsvik LOCA test series focussing on the new fuel fragmentation and dispersal (FFRD) phenomena. These Studsvik LOCA tests confirm the findings of the Halden LOCA test series although heating of the Studsvik specimens were indirect while in Halden tests it were both nuclear and indirect.

Objectives of this report are to summarise experimental findings on FFRD, to mechanistically interpret these findings on FFRD as far as available experimental data allow such interpretations, to discuss the applicability of such findings to reactor condition, to identify lacking experimental investigations, to identify thresholds for occurrence of FFRD phenomena, to discuss the necessity for modelling efforts as well as to finally discus potential consequences of FFRD for LOCA safety analyses.