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).
Highlights
Nowadays, computer codes are widely used for the determination of spent fuel nuclide inventory, decay heat, fuel loading analysis of nuclear reactors, among other studies [1,2,3]
Regarding the second exercise, where a 3 × 3 configuration of fuel assemblies is being 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%
The study of the impact that changing the surroundings of either a single fuel assembly or, on the other hand, the impact that changing the surroundings of a fuel assembly batch group has on the prediction of the decay heat, nuclide inventory, and neutron emission rates, was performed along a hypothetical scenario consisting of 4 cycles with a final 5 year cooling period of time
Summary
Computer codes are widely used for the determination of spent fuel nuclide inventory, decay heat, fuel loading analysis of nuclear reactors, among other studies [1,2,3]. The study of the impact that changing the surroundings of either a single fuel assembly (by means of changing the albedo) or, on the other hand, the impact that changing the surroundings of a fuel assembly batch group (by imposing a reflector in the middle of the configuration) has on the prediction of the decay heat, nuclide inventory, and neutron emission rates, was performed along a hypothetical scenario consisting of 4 cycles with a final 5 year cooling period of time This parametric study was carried out solely with the SERPENT2 code [9], and one of the main objectives is to assess the relative variation that exist between such depleted observables with respect to other ones that have been previously computed from an assembly modeled with full-reflective boundary conditions (i.e. albedo equal to unity), and that was ran for the same cycle scenario [3]. Another important objective of this work is to verify if by considering all possible materials that contain the same type of fuel as a single “burnable” region, the computation of the addition of the aforementioned observables of interest differ too much (due to the change of albedo or type of boundary), from the case where separate “burnable” regions containing fuel pins of the same type where instead consider for the integral computation of the results
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