Issues Along the Way

Abstract

Early in 1969 Commissioner Johnson and I became concerned that in the headlong rush to develop an economical fast breeder reactor, the AEC program might be allowing insufficient time to resolve questions of safety. We were aware of some inherent features of the LMFBR concept that implied a certain hazard and of other features that argued for inherent safety. Implying hazard was the fact that breeders would operate at much higher enrichment levels than conventional reactors, increasing the likelihood that a partial melting of fuel could lead to a runaway chain reaction. Another possibility was the sequence that caused the EBR-1 meltdown in 1955, when heat was generated faster than it could be carried away by the coolant. Further, we knew that the liquid metal coolant would react violently upon any contact with air or water, so that a coolant leak could be a serious danger. These factors in combination raised the specter of a possible accidental explosion. Conducive to safety was the fact that the liquid sodium coolant would not be kept under high pressure, thus reducing the likelihood of leakage. It also appeared that LMFBRs would be self-regulating to the extent that any increase in the temperature of the fuel in the core would be accompanied by an increase in the rate at which neutrons were absorbed by uranium-238, thus reducing the rate of power production. Further, studies seemed to indicate that any explosion that might occur would be of small magnitude, likely to be contained within the reactor vessel and almost certainly within the walls of the reinforced concrete containment building.¹