We investigate a new approach for estimating temporal responses in kinetic Monte Carlo transport methods. This approach employs functional expansion tallies, where particle scores generated during Monte Carlo simulations are projected onto a set of orthogonal basis functions, enabling continuous representations of temporal responses of interest. The key idea is that, by inferring a continuous shape for these responses, a gain in estimation efficiency can be achieved in time-dependent neutron transport problems compared with the standard histogram approximation.A range of orthogonal basis functions were investigated both in terms of their practical viability within the Monte Carlo framework and their theoretical convergence rates relative to the histogram-based approach. The method was implemented in SCONE and applied to a variety of time-dependent test problems, allowing for detailed comparisons between the functional expansion tallies and the histogram approximation under different conditions. These included target responses with varying degrees of smoothness and temporal gradients across the domain.The results demonstrate that functional expansion tallies can offer significant variance reduction compared with the standard histogram approximation, thereby improving the trade-off between simulation time and estimation accuracy. In particular, the gain in relative performance scales with the smoothness of the underlying response to be estimated, supporting the theoretical basis for the method and its suitability for problems involving smooth dynamic behavior.
The U.S. Department of Energy Office of Nuclear Energy's Office of Spent Fuel and High-Level Waste Disposition is examining a set of system options and conducting supporting analyses to inform the development of an integrated waste management system, which may include one or more federal staging facilities (FSFs) for used nuclear fuel (UNF) sited using a collaborative siting process. This paper focuses on the ongoing activities in two systems engineering and analysis work areas: (1) data and tools development, validation, and maintenance and (2) systems engineering execution. Within the first work area, the STANDARDS 5.0 UNF data and analysis tool, formerly known as UNF-ST&DARDS, is being developed as a foundational resource to assist in the management of UNF data. It has the key capability to model UNF throughout the entire back end of the fuel cycle. STANDARDS also includes several compatible analysis tools for the time-dependent characterization of UNF and related systems by interfacing with the SCALE code system for nuclear analysis and COBRA-SFS for thermal analysis. Also, within the data and tools area is the Next Generation System Analysis Model (NGSAM), which is an agent-based simulation software tool expressly designed to be capable of modeling the waste management system, including the transportation of UNF to and from a FSF. NGSAM has been developed to enable informed decision making by providing the capability to analyze various potential system options for the management of UNF and high-level radioactive waste. Finally, in the systems engineering execution area, the team has begun to apply a disciplined systems engineering approach at the system level along with supporting analysis to guide the development of the FSF project requirements (including associated transportation infrastructure). Systems engineering principles and practices and their adaptation/application to design and development activities will ensure that the waste management system is effectively implemented as work proceeds. Other activities include investigating the implications of changes in various assumptions and parameters related to waste management systems, such as UNF acceptance rates, receipt logic, facility capacities and capabilities, use of standardized canisters, and different assumed facility operation start dates.
In the present study, series of Sm2O3-doped borate-based glasses with the composition of B2O3-MgO-ZnO-BaO-Sm2O3 (BMZS) were synthesized using the melt quenching technique to determine their gamma-ray shielding effectiveness. The densities of the glasses increased from 3.950 g/cm3 (BMZS1) to 4.291 g/cm3 (BMZS4) with increasing BaO, which increased the probability of photon interaction. The gamma-ray attenuation parameters were obtained using a high-purity germanium detector at photon energies of 662, 1173, and 1332 keV. The results of the study indicate that the addition of BaO brings about increases in the density of the glasses and also greatly improves the attenuation parameters. The BMZS4 sample (35 mol % BaO) was the densest sample prepared (4.291 g/cm3) and provided improved gamma shielding properties, as indicated by the increasing linear attenuation coefficients (0.329 cm-1), reducing the half value layer (2.105 cm at 662 keV) and the increased mean-free-path and tenth value layer values. The experimental mass attenuation coefficients were in agreement with theoretical data with typical deviations between 2% and 5%. The BMZS4 sample produced superior attenuation performance values when compared to the previous glass systems (NZBC and BNASK) in all values of the measurements undertaken. In conclusion, BaO-rich BMZS glasses may provide exciting lead-free candidates for reliable gamma-ray shielding applications, with BMZS4 providing the best overall performance.
