# Burnup Credit Evaluation for BWR Spent Fuel from Full Core Calculations
## 6 Conclusions  
In the given study, the authors created a BWR full core reactor model based on the information available in open source. Since the fuel reloading procedure is commercially sensitive information, especially for modern reactors, the authors developed and applied a few different shuffling procedures to estimate the possible spread/variation of the fuel-discharged burnups. The analysis showed that the loading pattern from [18], used as a basis for this study, required minor adjustments to eliminate the assemblies-outliers. Overall, seven reloading patterns were analysed, two for the initial loading map and five for the adjusted one. The FA-discharged burnup distribution for the adjusted map was optimal (in terms of fuel utilisation) under the SP_A shuffling procedure with the burnup range \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**BUC Approach**} & \multicolumn{2}{c}{**Reactivity Gain, pcm**} \\ \cline{2-3}  & **SP\_A\_New** & **SP\_C\_New** \\ \hline Fresh fuel & 38,503 & 37,384 \\ Peak reactivity & 20,097 & 18,977 \\ Realistic FA at the peak reactivity & 16,179 & 15,060 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The full core reactivity gain for the suggested BUC of the core approach in comparison with approximate ones. Figure 11: The normalised reactivity gain of the burnup credit (BUC) of the core approach in comparison with the fresh fuel, peak reactivity, and the peak reactivity of the realistic FA model approaches for BWR fuel for least optimal (a) SP_C_new and most optimal (b) SP_A_new burnup distributions. 47.5 to 54.5 GWd/tU and least optimal under the SP_C procedure, with the burnup range 34.5 to 59 GWd/tU. The SP_B and mixed SP_A/SP_B shuffling procedures are defined as potentially optimal drafts. To achieve an industrially applicable optimum, the loading map requires further adjustments. A single BWR FA model was analysed in the 2D lattice and 3D nodal approaches. The aim was to identify the impact of the increased level of FA model complexity on the criticality curve and the BUC. The results showed that the peak reactivity appears, by 10 GWd/tU, earlier on the criticality curve for the 3D BWR FA model with burnable poison in comparison with 2D lattice model and the criticality at the peak is substantially reduced. The given result coincides with the conclusions from [16]. Thus, the introduction of more detailed features in the BWR FA model using a nodal code can decrease the conservatism of the peak reactivity method when calculations are performed using the 2D lattice approach. Further investigation of the 3D model's criticality curve revealed the presence of a second spike in criticality which, according to the power profile analysis, occurs due to the fuel depletion from the vanished layer (upper core). Finally, the authors estimated the potential benefit from applying the burnup credit method to the modern BWR SF using the criticality curve for the 3D BWR FA model (M3) and the discharged burnup distributions obtained from the full core nodal simulations with two shuffling procedures, SP_A and SP_C. The results showed that the average reactivity gain in comparison with the fresh fuel and peak reactivity approaches is close for both SP_A_new and SP_C_new burnup distributions, even if the loading patterns are very different. The minimum reactivity decrease was 15,000 pcm or 14% in the SP_C_new case in comparison with the peak reactivity approach with the realistic FA model, while the maximum was 38,500 pcm or 35.5% for the SP_A_new case in comparison with the fresh fuel approach. On the other hand, more fuel assemblies from the distribution with the optimal shuffling scheme SP_A achieve the same level of burnup and thus show the larger reduction in reactivity in comparison with the standard BUC approaches for the BWR, and thus, future task loading is estimated to be less sensitive. Conceptualization, A.D. and B.M. ; methodology, A.D. and D.L. ; software, A.D.; formal analysis, A.D.; investigation, A.D. and D.L.