Abstract
Laboratory examination of one of the first core debris samples removed from the Three Mile Island Unit 2 (TMI-2) reactor was performed as part of a series of in-depth evaluations of postaccident core damage.
Sample analysis has given new information on the quenched high- temperature reaction products formed during the TMI-2 loss-of-coolant accident. The rapid exothermic steam corrosion of Zircaloy and stainless steel cladding and localized uranium dioxideZircaloy reactions are considered the main processes. The sample was removed from a depth of three inches below the top surface of the rubble bed along the axial centerline of the reactor. The debris was composed primarily of granular ceramic fragments, resolidified metallic and "lava rock-like" materials. About one-fourth of the particles contained up to 20% open porosity and appeared to be high temperature reaction products from portions of two or more core components. Uranium dioxide fuel pellet fragments, oxidized cladding, or combinations with reaction product material were also identified.
The sample contained free-flowing particles ranging from 1 cm to less than 45 micrometers, with an average size of 2 mm. Debris material was mainly composed of uranium, zirconium, and iron. Nickel, chromium, silver, tin, aluminum, and indium were also present in smaller amounts. All of these elements were present in the original core materials.
The observed results are discussed with respect to published analytical predictions.
