STUDIES OF CONTROL, POWER SHAPING, AND BURNOUT BEHAVIOR FOR AETR

Abstract

Parametric studies were carried out to optimize the performance and obtain an understanding of the nuclear characteristics of the Advanced Engneering Test Reactor (AE TR) design concept. Two-dimensional two-group diffusion theory calculations were performed for the purpose of evaluating the worth of the droppable safety reflector. Removal of the D/sub 2/O from the 4-in. thick safety reflector region from the level of the top of the active core to the level of the bottom of the active core with a fully poisoned shim reflectcr region resulted in a decrease in the multiplication factor from 0.9911 to 0.7515. Removal of the D/ sub 2/O from the 4-in. thick safety reflector region with a clean D/sub 2/O shim reflector resulted in a decrease in the multiplication factor from 1.18 to about 1.04. This indicated that the safety reflector wonth decreases as the boron poison is removed from the shim reflector during the core life. An iterative procedure using one-dimensional three-group dlifusion theory calculations was performed to determine a graded fuel distribution which produces a flat radial power density. The calculations were terminated when the maximum-toaverage power density was reduced to 1.018. Burnup calculations, using the CANDLE one- dimensional, four-group diffusion theory depletion code, were performed for flat and graded fuel cores, each containing 12 kg U/sup 235/ initially. The radial variations in the fuel distributions and the power density distributions during the fuel cycle were determined at several times. The effectiveness of a burnable core poison to supplement the soluble-poison shim control in the reflector was investignted. Using a Bi/sup 10/poisoning of 0.075 reduced the initial multiplication factor by 5.9%. By adjusting the fuel loading and optimizing the burnable poison, it appeared that the 19-day fuel cycle is feasible. (M.C.G.)