A Scenario of the Three Mile Island Unit 2 Accident

The primary objective of the U.S. Department of Energy Three Mile Island Unit 2 (TMI-2) research program, conducted by the EG&G Idaho TMI-2 Accident Evaluation Program, is to develop a comprehensive and consistent understanding of the TMI-2 accident. The accident scenario developed from this research is presented, including information relative to (a) the progression of core damage leading to a consolidated region of partially molten core material, (b) continued heatup of this consolidated region leading to extensive melting of the core, (c) failure of the supporting crust encasing the molten core material and relocation of 15 to 20 tonnes of molten core material into upper and lower core support assemblies and the lower plenum, and (d) interaction of molten core material with coolant and support structures in the lower plenum. Fission product release from fuel during the accident is also discussed.