Application of burnable absorbers in an accelerator-driven system

The application of burnable absorbers (BAs) to minimize power peaking, reac tivity loss, and capture-to-fission probabilities in an accelerator-driven waste transmutation system has been investigated. Boron-IO-enriched B4C abs orber rods were introduced into a lead-bismuth-cooled core fueled with tran suranic (TRU) discharges from light water reactors to achieve the smallest possible power peakings at beginning-of-life (BOL) subcriticality level of 0.97 Detailed Monte Carlo simulations show that a radial power peaking equa l to 1.2 at BOL is attainable using a four-zone differentiation in BA conte nt. Using a newly written Monte Carlo burnup code, reactivity losses were c alculated to be 640 pcm per percent TRU burnup for unrecycled TRU discharge s. Comparing to corresponding values in BA-free cores, BA introduction dimi nishes reactivity losses in TRU-fueled subcritical cores by similar to 20%. Radial power peaking after 300 days of operation at 1200-MW thermal power was <1.75 at a subcriticality level of <similar to>0.92, which appears to b e acceptable, with respect to limitations in cladding and fuel temperatures . In addition, the else of BAs yields significantly higher fission-to-captu re probabilities in even-neutron-number nuclides. Fission-to-absorption pro bability ratio for Am-241 equal to 0.33 was achieved in the configuration s tudied. Hence, production of the strong alpha-emitter Cm-242 is reduced, le ading to smaller fuel-swelling rates and pin pressurization. Disadvantages following BA introduction such as increase of void worth and decrease of Do ppler feedback in conjunction with small values of beta (eff), need to be a ddressed by derailed studies of subcritical core dynamics.