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The TMI-2 Accident Evaluation Programme was originally set up by the US Department of Energy, then part of the programme was later broadened into an international collaboration project under the aegis of the OECD Nuclear Energy Agency (NEA). The initial programme was concerned primarily with the core damage progression analysis, metallographic studies of core debris samples and structural materials, as well as the mechanisms controlling fission product behaviour during the accident. However it became apparent after the programme had been established that the TMI-2 accident, which occurred 28 March 1979, had progressed further than believed. Large quantities of molten core material had relocated from the core to the lower plenum of the reactor pressure vessel, and thermal damage had occurred to instrument structures in the lower head region; hence the US Nuclear Regulatory Commission (USNRC) asked NEA to set up a second international collaborative project, the Three Mile Island Vessel Investigation Project (TMI-VIP) to examine additional aspect of the question.
The new programme, subject of the OECD/TMI-VIP Project, was designed to evaluate the potential modes of failure and the margin to failure of the TMI-2 reactor vessel during the TMI-2 accident. The conditions and properties of material extracted from the lower head of the TMI-2 reactor pressure vessel were investigated to determine the temperature conditions and the extent of the damage by chemical and thermal attack on the lower head, as well as the margin of structural integrity of the vessel during the accident.
This project enabled progress in three directions: a better view and understanding of the TMI-2 accident scenario over the time (it took 8-10 years to discover the potential for lower head failure), the technical conclusions of the TMI-2 VIP (no evidence of significant bottom vessel creep and additional cooling area provided with debris bed formation) and the broad significance of these findings for accident management (importance of maintaining cooling water and importance of limiting vessel pressure).
Project countries: Belgium, Finland, France, Germany, Italy, Japan, Spain, Sweden, Switzerland, United Kingdom, United States.
Project period: 1st January 1988 - 31st March 1993
The distribution of this package is restricted and subject to prior approval.
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Keywords: core damage, fission products, reactor pressure vessel.