Burnable absorber element (Gd and Er) use in the WWER-type reactor to increase the refueling time

Abstract

In a WWER-type pressurized water reactor, high-neutron-absorbing materials can compensate for the excess reactivity. Theoretical and computational analyses were conducted in this article to use burnable absorbers placed in a fuel rod to reduce the reactivity margin for extending refueling time for WWER-type reactors. To investigate the reduction of the reactivity margin, the fuel burnup calculation was performed without a burnable absorber and with a combination of a variety of burnable absorbers, namely natural Gadolinium (Gd) and Erbium (Er), applying a simplified GETERA program. The calculation found that the variation of the quantity of the burnable absorber (Gd, Er) inside the fuel assemblies governs the reactivity margin for the fuel burnup and increases the efficiency of Uranium fuel (UO2). The combined use of Gd and Er leads to a smoother decrease in reactor reactivity due to a smaller Er absorption cross section, which makes it possible to reduce the total mass of Gd in the fuel element and reduce the blocking effect. In the calculation, Gd concentrations employed in the computation at 1.5% and 3%, while Er concentrations were used within the range of 0.1%–0.6%.