Examination of melted fuel rods and released core material from the first Phebus-FP reactor accident experiment

In the first Phebus test, 20, one meter long, lightly irradiated UO2 fuel r ods and a central Ag-In-Cd control rod were heated by fission power to an e stimated 3000 degrees C. In this paper results are reported for the composi tion of the molten cerium pool in the lower part of the test assembly and d eposits of released core material in the vertical line. The examination tec hniques used comprised optical microscopy, scanning electron microscopy, X- ray microbeam analysis, inductively coupled plasma mass spectroscopy, X-ray diffraction and gamma-spectroscopy. The matrix of the cerium pool was a si ngle phase of composition (U0.50Zr0.47Fe0.02Y0.01)O2 +/- x. Inclusions in t he solidified pool were ReIr alloys, W with minor concentrations of Fe and Ni and spinels of Cr, Fe and Ni. The main constituents of the deposit in th e vertical line were Re, Ag, In and Sn. Tin formed a thin layer on the stee l surface. Droplets of the cerium matrix phase were embedded in the deposit . Traces of Cs-137 were mainly responsible for the gamma-activity of the de posit. (C) 2000 Elsevier Science B.V. All rights reserved.