Three Mile Island Reactor Pressure Vessel Investigation Project (TMI-VIP)
Joint project

Long-handled tools are used to remove the damaged core from the TMI unit 2 reactor in the US. Samples taken from the fuel and the reactor vessel are examined to provide information about the Behaviour of molten core material.


On 28 March 1979, a partial meltdown of the Three Mile Island unit 2 (TMI-2) reactor occurred at the TMI nuclear power plant near Harrisburg, Pennsylvania, United States.

A TMI accident evaluation programme was originally set up by the US Department of Energy (US DOE), then part of the programme was later broadened into an international collaboration project under the aegis of the Nuclear Energy Agency (NEA). The initial programme was concerned primarily with 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 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 (US NRC) asked NEA to set up a second international collaborative project, the Three Mile Island Vessel Investigation Project (TMI-VIP) to examine the additional aspects of the problem.

The 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 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.

The project enabled progress in three directions:

  • a better view and understanding of the TMI-2 accident scenario over 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);
  • the broad significance of the findings for accident management (importance of maintaining cooling water and importance of limiting vessel pressure).

Project data

The data abstract is available upon request to the NEA Data Bank.

External reports

  • Wolf, J.R., et al., TMI-2 Vessel Investigation Project Integration Report, Idaho National Engineering Laboratory, October 1994,
  • "Three Mile Island Reactor Pressure Vessel Investigation Project- Achievements and Significant results" - Proceedings of an open forum sponsored by the OECD Nuclear Energy agency and the United States Nuclear Regulatory Commission - Boston (USA) 20-22 October 1993.

Belgium, Finland, France, Germany, Italy, Japan, Spain, Sweden, Switzerland, United Kingdom and the United States.

Project period

1 January 1988 - 31 March 1993


USD 9 million