Determination by Thermochemical Calculation of Speciation and Deposition of Fission Product and Structural Material during the Vercors HT 1 Experiment

This paper reports the results of a study aimed at the determination of the theoretical deposition of fission product and structural material along the experimental circuit during the Vercors HT 1 transient. The study is formed by two parts as follows: -the former is constituted by a series of thermochemical calculations carried out to achieve the speciation for the chemical elements released during the test in the experimental conditions given; -the latter is relative to the interpretation of speciation in order to establish the species deposition as a function o temperature along the circuit. Basic data for calculation involve 15 chemical elements plus those or cover gas and a total time of 14400 seconds. The temperature is comprised in the range 500-2900°K, The thermochemical calculations have been made by the HSC 5.1 Programme. The following items have been included for each element: a) Equilibrium composition, obtained by the HSC Programme calculation. Note that this programme takes into account melting and boiling and no other phenomena. b) Mass balance, derived from a. c) Total gaseous and condensed fraction of the element as a function of temperature, derived from b). d) Total quantity condensable of each element on selected parts (at random) of the experimental facility (Pipes 1, l0, 20, 30, and 36), derived from c). e) Total quantity condensable of each species on significant part of the experimental facility, derived essentially from b). All condensation results have been collected in the following summary tables: - All species condensation, g - List of all species condensed on each pipe, g - Total quantity of element in species condensed The results of calculation indicate the condensation of 30 species. U, So, Mo, CsOH, SnO,Sn02, and Cs2Te are the condensed species present to a great extent.