TMI-2 defuelling conditions and summary of research findings

The Three Mile Island Unit 2 accident was severe, with extensive melting of fuel, release of fission products, and relocation of a large quantity of molten fuel material onto the reactor vessel lower head. This molten material challenged the integrity of the reactor vessel, which remained intact. The post-accident condition of the plant presented an extremely difficult and complex plant recovery. Core defuelling necessitated the development and use of tools and the application of methods not used previously in the nuclear industry. During the past nine years, the TMI-2 accident has been a unique, invaluable source of information for improving and expanding the base of knowledge on severe accidents in power reactors. This paper presents the plant's post-accident condition, summarizes the primary results of research on progression of core damage and fission product behaviour during the accident, and discusses the approach to defuelling the reactor. (author). 25 refs, 4 figs, 1 tab