Laser-Pulse Melting of Nuclear Refractory Ceramics

An accurate method for melting-point measurement of refractory nuclear ceramics was developed, based on laser-pulse heating and thermal arrest detection. The temperature measurement is performed by a combined use of a brightness pyrometer and a high-speed spectrometer working in the range of 500 to 900 nm. This method provides both the true temperature and the spectral emissivity function of the examined materials. Pure siIntered MgO and a Mg:Am mixed oxide were first measured. The resulting melting point of the former (2350±20 K) is significantly higher than that commonly recommended and decreases with the addition of americium. Furthermore, UO2 irradiated to 37,000 MWd/t and submitted to a reactor loss-of-coolant test was investigated: the melting point decreases from 3120 K, in the as-fabricated state, to 2950 K. Both fresh Zr:U mixed oxides and ‘‘corium’’ lava from a reactor meltdown experiment were also investigated.