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Highlights • The burnup credit calculations for PWR spent fuel assemblies were performed. • Six single effects and eight compound effects were studied. • The Δ k caused by both single and compound effects were investigated. • The mechanisms of both single and compound effects were studied. Abstract This study attempted to thoroughly investigate the impact of single and compound effects on burnup credit calculations for PWR spent fuel assemblies originating from various operating parameters. Three operating parameters were considered, including fuel temperature, boron concentration, and axial burnup profile. The single and compound effects defined in this study represent the influence caused by simultaneous variations of one and multiple operating parameters on the curve of effective multiplication factor (k eff) versus burnup (B), respectively. All the calculations were performed using SCALE 6.1 computer code together with the ENDF/B-VII 238-group data library. In addition, two geometrical models were established based on the Westinghouse 17 × 17 PWR optimized fuel assembly and GBC-32 storage cask. The results revealed that an increase of fuel temperature or boron concentration induces a positive reactivity deviation (or the change of k eff , Δ k), the opposite is also true when a decrease of fuel temperature or boron concentration is considered. Moreover, the utilization of non-uniform axial burnup profile leads to a positive Δ k. Additionally, in most of the compound effects, Δ k resulting from the compound effects was not a linear summation of the Δ k 's resulting from the associated single effects. In particular, such Δ k discrepancy increases as B increases, which could influence the precise assessment of burnup credit to some extent. The mechanisms of both the single and compound effects were studied by the analysis of the spectral distribution of fission. From this analysis, an increase of either fuel temperature or boron concentration leads to a harder neutron spectrum, while a non-uniform axial burnup profile leads to a softer one. [ABSTRACT FROM AUTHOR]

• The varying amounts of proton beams result in different minor actinide burnup. • Single proton beam leads to an uneven neutron flux on the fuel assembly. • The dual proton beam possesses the highest neutron importance and burnup. This study aims to identify the optimal beam design for incinerating the long-lived minor actinides in Accelerator-Driven System (ADS). All the analyses were performed using the MCNP6.1 code with cross-section library ENDF/B-VII. In this study, a depletion method for ADS was conducted and analyses were exercised to investigate the burnup performances for the various arrangements of a three-proton beam design. The influences of the various arrangements of the three-proton beam design were used as a criterion for comparison. It was found that the dual proton beam arrangement demonstrated the best depletion result for the incineration of minor actinides. [ABSTRACT FROM AUTHOR]

Abstract: This study performs an investigation of geometry homogenization simulation using MCNP5 v1.51 and SCALE6 on the HTR-10 criticality calculations and focusing on the impact of geometry homogenization on k eff and neutron spectrum. The data libraries employed in this work are both continuous ENDF/B-VI respectively in MCNP5 and SCALE6. Six models, which are Model 1 – heterogeneous model, Model 2 – TRISO coating and graphite matrix homogenized model, Model 3 – TRISO homogenized model, Model 4 – fuel zone of fuel ball homogenized model, Model 5 – fuel ball homogenized model, and Model 6 – core homogenized model, are performed correspondingly by using MCNP5 and SCALE6 on the homogeneous effect analysis in HTR-10. The results revealed that the differences of k eff between MCNP5 and SCALE6 are all less than 300pcm. The small differences of k eff, neutron spectra, and also the consistent discrepancies of neutron spectra between each homogenized model (Model 2–6) and Model 1 show the good agreement of MCNP5 with SCALE6 in the geometry homogenization. [Copyright &y& Elsevier]

• A modified simulation model in MCNP 6.1 was developed for the dynamic HTR-10 core. • Applying the composition library can simplify processes with accurate results. • Due to longer residual time, the discharge burnup in the outer channel is higher. • Core power distribution using multi-pass refueling is more uniform compared to OTTO. This study aims to precisely investigate the core characteristics of HTR-10 using an online-refueling fuel loading scenario through an innovative approach that incorporates a pre-generated fuel composition library. HTR-10 is an experimental high-temperaturegas- cooled pebble-bed reactor constructed in China. Applying multi-pass fuel loading scenario, the pebbles in HTR-10 pass through the core several times via onlinerefueling. In this study, we proposed a model that simulates the dynamic operation of HTR-10 by using continuously static calculations. The model was constructed by dividing the core into 3 flow channels with different amounts of horizontal zones according to the residence time of fuel pebbles. However, random distribution of the pebbles with various burnup values complicates the refueling process. In order to simulate online-refueling more conveniently, a comprehensive method based on multipass fuel loading scenarios was thus developed. Firstly, a pre-generated fuel composition library containing the content of both actinides and fission products of fuel pebbles as a function of burnup, was built by implementing full core depletion calculations. During the refueling processes, a specific ratio of discharged fuel pebbles to fresh fuel pebbles was reloaded into the top zones. Thus, the average burnup values in the top zones can be resulted by considering the supplement of fresh fuel pebbles. Eventually, the fuel composition in the top zones were obtained by interpolating the average burnup value from the pre-generated library. In this study, all the calculations were performed using the MCNP6 computer code together with the ENDF/B-VII continuous energy neutron data library. The results revealed that the core reached a state of equilibrium after seven refueling processes with an increased rate of volume fraction. Our findings correspond to those of other studies. Another model constructed by locating the actual distribution of fresh pebbles also confirms the verification of the refueling method. Eventually, the burnup characteristics as well as the power and flux distributions in the HTR-10 core were analyzed using the simulation method. [ABSTRACT FROM AUTHOR]