BOUNDARY CONDITION MODELING EFFECT ON THE SPENT FUEL CHARACTERIZATION AND FINAL DECAY HEAT PREDICTION FROM A PWR ASSEMBLY

¹ SCK-CEN (Belgian Nuclear Centre) Boeretang 200, 2400 Mol, Belgium
² Jožef Stefan Institute Jamova cesta 39, 1000 Ljubljana, Slovenia
³ EC Joint Research Centre Geel Retieseweg 111, 2440 Geel, Belgium

ahsolis@sckcen.be
klemen.ambrozic@ijs.si
dusan.calic@ijs.si
luca.fiorito@sckcen.be
bor.kos@ijs.si
marjan.kromar@ijs.si
peter.schillebeeckx@ec.europa.eu
alexey.stankovskiy@sckcen.be
gasper.zerovnik@ec.europa.eu

Published online: 22 February 2021

Abstract

In this paper, two main exercises have been carried out to describe the effect that varying an albedo boundary condition has in the computation of observables such as decay heat, neutron emission rate and nuclide inventory from a PWR fuel assembly (or a configuration of assemblies) during a depletion scenario. The SERPENT2 code was then employed to emphasize the importance of modeling a proper boundary condition for such purposes. Moreover, the effect of taking into account more than a single fuel-pin region for depletion studies while varying the type of boundary condition, was also accounted for. The first exercise has the main objective of comparing in a single fuel assembly the albedo variations ranging from 1.1 up to full vacuum conditions. By comparing to the reference assembly (considered to be the case of full reflective conditions), relative differences up to +17% were observed in decay heat and up to almost -30% in neutron emissions. Also, a clear dependence on the albedo was detected if more than one depletable zone was considered while computing the integral value of observables of interest. Regarding the second exercise, where a 3 × 3 configuration of fuel assemblies is being now considered with a reflector section in the middle, a negligible effect on the observables was observed for the single fuel pin zone case; instead, an effect in the ²⁴⁴Cm computation when analyzing two fuel pin-zones produced a change in the neutron emission rate during cooling time up to 2.5% (while comparing it to the reference single assembly case).