Understanding the TMI-2 accident: an overview

The accident at Three Mile Island Unit 2 (TMI-2) on March 28, 1979 has had a profound impact on the nuclear power industry despite the fact that the health consequences to the public were insignificant. There is considerable benefit to the nuclear power industry in understanding the progression of this severe core damage accident and its relationship to the very small releases of radioactivity to the environment. An overview of our current understanding of the TMI-2 accident is presented in this paper along with a discussion of the significance of that understanding. The damage state of the reactor, our proposed best estimate accident scenario, temperature determinations in the core debris and in structural materials in the upper plenum, and distribution of fission products in the reactor are presented.