Boundary Condition Modeling Effect on the Spent Fuel Characterization and Final Decay Heat Prediction From a PWR Assembly

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).

On the estimation of nuclide inventory and decay heat: a review from the EURAD European project

“…-In reference [32], a similar case of a PWR UO 2 assembly (4.0% enrichment, 51 MWd/kg) is studied, and changes in simulation codes modify the SNF decay heat by a maximum of 2%. For the same assembly, results in reference [28] indicate that changes in boundary conditions (from over-reflective to fullvacuum cases) moderately affect the assembly decay heat below 20 years of cooling time (less than 3%), but induce strong changes for longer cooling time (up to 25%). Such extreme changes in boundary conditions are likely to be unrealistic, and more reasonable changes (such as realistic surrounding assemblies vs.…”

“…-17 PIE samples were used to calculate nuclide compositions, uncertainties, and biases, for 4 ARIANE samples (GU1, GU3, BM1, BM3), 8 ENRESA samples (not available in SFCOMPO), the U1 PROTEUS sample (also not available in SFCOMPO), 2 Takahama samples (SF95-4 and SF95-5), and 2 Gundremmingen samples (B23-A1-I2680 and C5-B23-K2680), with the addition of 2 computational cases (S1.PWR and krsko.PWR [14,15]), -271 calorimetric measurements from CLAB (labelled herein as CLAB-2006), GE-Morris, HEDL facilities and the "SKB-Vattenfall" blind test were analyzed for the assembly average decay heat [16][17][18][19], and the decay heat from the 17 (not measured) PIE samples. Detailed studies were independently published for a number of cases, see references [20][21][22][23][24][25][26][27][28][29][30][31][32]50]; summaries are presented in Tables 1 and 2. Regarding sensitivity studies presented in Table 1, considerable efforts have been made to address the effect of the irradiation history, as-built manufacturing data and effect of various calculation model approximation on the SNF characterization.…”

Spent nuclear fuel management, characterisation, and dissolution behaviour: progress and achievement from SFC and DisCo

“…For decay heat, the calorimetric measurements from CLAB (Swedish Central Intermediate Storage Facility), GE-Morris, and HEDL (Hanford Engineering Development Laboratory) were considered, leading to more than 250 cases. To support the recommendations of this subtask, some studies were already published, see references [3][4][5][6][7][8][9][10][11][12][13][14][15]. A global review of the The aim is to produce NDA systems that can be used to provide experimental data to validate the performance of the codes (including nuclear data) and to verify the declared design and operational history of the assemblies.…”