Analysis of an unmitigated large break loss of coolant accident (LBLOCA) with the non-mechanistic failure of passive cooling for the APT Spallation Target

In order to support the Programmatic Environmental Impact Statement, an accident analysis has been performed for the Accelerator Production of Tritium (APT) Spallation-Induced Lithium Conversion (SILC) Source. This report presents a lumped-parameter analysis that predicts the thermal response of the source to a large-break LOCA. The accident scenario assumes the break to occur in the cold leg outside the source basin and the pipe break is immediately followed by the tripping of the proton beam and the activation of the source-basin flood system. The calculations were performed for a ``beyond-design-basis event`` which further assumes the failure of all other active cooling systems, and the failure to establish natural circulation in the unbroken loop. Calculations show that the source rods remain flooded in heavy water until 44 hours after the LOCA. At this time, the source rods begin to be uncovered and at 48 hours into the accident the source rods are completely boiled dry. The average source temperature reaches a maximum value of 303 C at 57 hours. Thereafter, the source rods begin to cool since the heat transfer to the basin water is sufficient to remove all the decay heat from the source. It is estimated that by this time a maximum of 27% of the lead inventory (6,558 kg) in the source rods can be expected to melt. This molten material, assuming that it can get out of the aluminum cladding, will fall to the D{sub 2}O-filled bottom header, quench rapidly, and remain in a coolable state