Dysprosium as a resonance absorber and its effect on the coolant void reactivity in Advanced Heavy Water Reactor (AHWR)

Dysprosium has been used as a slow neutron absorber in the fuel assembly of Advanced Heavy Water Reactor (AHWR) to achieve a negative coolant void reactivity. Dysprosium as occurring in nature has as many as seven isotopes namely, 156Dy, 158Dy, 160Dy, 161Dy, 162Dy, 163Dy, and 164Dy. Of these, the isotope 164Dy has the largest absorption cross section for thermal neutrons. In the past, nuclear data libraries used in our studies have considered only 164Dy isotope and this was sufficient for performing foil activation studies of Dy. The other isotopes of Dy have significant resonances and could affect the design. The treatment of the dysprosium isotopes with resonance tabulations is required for a more accurate estimation of the lattice characteristics like the coolant void reactivity. The use of resonance tabulations for the dysprosium isotopes and its effect on the coolant void reactivity of AHWR fuel cluster has been studied in this paper. Also, the treatment of the stand-alone structural rod with dysprosium as burnable absorber having resonance tabulations has been done for the first time.