Thermal properties of Three Mile Island Unit 2 core debris and simulated debris

Nagase, Fumihisa ; Uetsuka, Hiroshi

Thermal properties of molten and mixed core materials are required to be known for effective analysis of core damage in severe accidents at nuclear power plants. The specific heat capacity, thermal expansion, thermal diffusivity, and melting temperature were measured or estimated on the core debris samples of the Three Mile Island Unit 2 (TMI-2) reactor and simulated debris (SIMDEBRIS), which had chemical composition and porosity similar to the TMI-2 debris. The thermal diffusivity of the TMI-2 debris, which is mainly composed of (U,Zr)O, was as low as 10% to 25% of UO at room temperature but was comparable above 1500 K. The melting temperature of SIMDEBRIS was about 2840 K, which is equivalent to the liquidus temperature of (U,Zr)O with the same ZrO/UO ratio. Accordingly, other core materials less than 10% in weight were observed to have no influence on the melting temperature.