Damaged Fuel Experiment DF-1

Abstract

A series of in-pile experiments addressing LWR severe fuel damage phenomena has been conducted in the Annular Core Research Reactor (ACRR) at Sandia National Laboratories. The ACRR Debris Formation and Relocation (DF) experiments are quasi-separate effects tests that provide a data base for the development and verification of models for LWR severe core damage accidents. The first experiment in this series, DF-1, was performed on March 15, 1984, and the results are presented in this report. The DF-1 experiment examined the effects of low initial clad oxidation conditions on fuel damage and relocation processes. The DF-1 test assembly consisted of a nine-rod square-matrix bundle that employed PWR-type fuel rods with a 0.5-m fissile length. The fuel rods were composed of 10% enriched UO{sub 2} pellets within a zircaloy-4 cladding. Steam flowed through the test bundle at flow rates varying between 0.5 and 3 g/s, and the ACRR maintained a peak power level of 1.5 MW during the high temperature oxidation phase of the test inducing {approximately}8.5 kW fission power and {approximately}20 kW peak oxidation power in the assembly. Visual observation showed early clad relocation and partial blockage formation at the grid spacer location accompanied by production of a dense aerosol.more » Posttest cross sections show liquefaction losses of fuel in excess of 10 volume percent, as well as large fractional losses of cladding material from the upper two-thirds of the bundle. The quantity of hydrogen measured during the test was consistent with the observed magnitude of cladding oxidation. Oxidation driven heating rates of 25 K/s and peak temperatures in excess of 2525 K were observed. The analyses, interpretation, and application of these results to severe fuel damage accidents are discussed. 27 refs., 118 figs., 23 tabs.« less