Role of core-disruptive accidents in design and licensing of LMFBRs

The role of core-disruptive accidents (CDAs) in design and licensing of liquid-metal-cooled fast breeder reactors is reviewed, including a description of CDA initiators, likely accident paths, core-meltdown energetics, and radiological consequences. It is concluded that (1) the probabilities of initiators leading to core meltdown should and can be made sufficiently low (objective, less than 10-6 per reactor-year) to reduce them to Class 9 accidents, (2) best-estimate analysis including design considerations should and can demonstrate the unlikelihood (objective, less than 10-2) of a postulated core meltdown leading to substantial energetics that would challenge the energy absorption capability provided by the primary-system design, i.e., the absence of energetic hydrodynamic disassembly and/or energetic fuel--coolant interactions, (3) the principal basis for the primary-system design should be set by functional requirements where any weak links in the resulting design should be upgraded to give an overall consistent system with an optimum energy absorption capability (essentially current practice) and not by arbitrary CDA energetics, and (4) on the basis of best-estimate analysis including design considerations, the objective should and can be to demonstrate long-term containment capability of the fuel debris following a postulated core-meltdown accident. This balanced approach is believed necessary, at least in the near term, to adequately demonstrate that the safety objective that the occurrence of radiological consequences outside the plant boundary in excess of acceptable levels must be less than 10-6 per reactor-year has indeed been achieved