STARTUP AND MIDLIFE MOCKUP EXPERIMENTS FOR SM-1, SM-1A, AND PM-2A WITH TYPE 3 ELEMENTS

The use of Type 3 fuel elements in the SM-1, SM-1A, and PM-2A reactors was evaluated by a series of critical mockup experiments. The burnable poison loading to meet required excess reactivity and shutdown margin was determined at core startup conditions. Measurements included control rod bank critical positions, bank calibrations, excess reactivity, shutdown margin for critical bank, stuck rod configurations, flux suppressor worth, temperature defect, and temperature coefficient at operating temperature and pressure. Midlife mockup experiments, made to compensate for fuel burnup, B burnup and fission product poison buildup, were performed to check the excess reactivity and shutdown margin at approximately the most reactive conditions during core lifetime. All cores meet the design requirements for adequate shutdown margin with one control rod fully withdrawn (stuck rod criterion) at any time during core life, and for excess reactivity of at least 3;% DELTA K at beginning of core life. (auth)