Two important issues in Performance Assessment exercises regarding the alteration of Spent Nuclear Fuel (SNF) are the contribution of Instant or better called Fast release Fraction (FRF) and the effect of High Burn-Up Structure (HBS). Therefore this paper focuses on the effect of HBS in FRF of a PWR irradiated in a commercial reactor with a mean Burn-Up (BU) of 48 GWd/tU. Additionally, determined FRF are compared with previous experiments performed with PWR with a mean BU of 60 GWd/tU, in order to evaluate the effect of BU on FRF.
In order to study the HBS contribution, static leaching experiments are performed with two samples prepared from different radial positions, labeled Core, central region and Out, enriched with HBS. Two synthetic leaching solutions, bicarbonate and bentonitic granitic groundwater are used under oxic conditions.
The estimated FRF are calculated from the determined Fraction of Inventory in Aqueous Phase (FIAP) taking into account the inventory determined experimentally for each fraction.
Higher release is observed for Core sample, which can be an indicative that HBS does not increase the RN release. With the exception of Rb and Cs, which release is higher at lower BU, no clear effect of BU is observed within the studied range.