Decay Interval Effect on Targets Containing Curium upon Subsequent Irradiation

摘要

The Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL) irradiates curium oxide targets in the High Flux Isotope Reactor (HFIR) to produce ~(252)Cf and other transuranium isotopes for research, industrial, and medical applications. These materials are produced in the flux trap of the HFIR, where the peak thermal-neutron flux is about 2.3 X 10~(15) neutrons/(cm~2 · s). The curium oxide is pressed with aluminum powder into pellets and loaded into aluminum target tubes. There are typically 35 pellets per target and 9 to 13 targets per "campaign." The oxide material, rich in the heavier isotopes of curium, also has small amounts of some isotopes of plutonium and americium. The composition of the oxide is determined through calorimetry and other analyses performed on the pellet and oxide batches. Time-dependent fission heat calculations, using the FORTRAN programs TCOMP and FCOMP, on the target with the greatest loading of curium oxide provide a thermal qualification for irradiation in the HFIR. The actinide composition and expected reactor power history are input, and the fission rates are output for each time step, which is then used to determine the peak fission rate. The reactor's central position is assumed for the target qualification. This "hottest" position, applied to a pellet, is mathematically extended to the whole target. For the current set of targets, the expected peak fission heating rate was found to occur on the first day of irradiation and to be well below (about 65% of) the allowable maximum.