Application of burnable absorbers in an accelerator-driven system

• The application of burnable absorbers (BAs) to minimize power peaking, reactivity loss, and capture-to-fission probabilities in an accelerator-driven waste transmutation system has been investigated. Boron-IO-enriched B4C absorber rods were introduced into a lead-bismuth-cooled core fueled with transuranic (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 equal to 1.2 at BOL is attainable using a four-zone differentiation in BA content. Using a newly written Monte Carlo burnup code, reactivity losses were calculated to be 640 pcm per percent TRU burnup for unrecycled TRU discharges. Comparing to corresponding values in BA-free cores, BA introduction diminishes reactivity losses in TRU-fueled subcritical cores by similar to 20%. Radial power peaking after 300 days of operation at 1200-MW thermal power was0.92, which appears to be acceptable, with respect to limitations in cladding and fuel temperatures. In addition, the else of BAs yields significantly higher fission-to-capture probabilities in even-neutron-number nuclides. Fission-to-absorption probability ratio for Am-241 equal to 0.33 was achieved in the configuration studied. Hence, production of the strong alpha-emitter Cm-242 is reduced, leading to smaller fuel-swelling rates and pin pressurization. Disadvantages following BA introduction such as increase of void worth and decrease of Doppler feedback in conjunction with small values of beta (eff), need to be addressed by derailed studies of subcritical core dynamics.

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transmutation

reactors

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