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The nomination period for the 2026 Nuclear News 40 Under 40 list is now open. The list aims to highlight people in the nuclear community who are making significant, early-career achievements. All nominations must be submitted online by 11:59 p.m. (CDT) on May 1, 2026.
Marco Tiberga, Simone Santandrea
Nuclear Science and Engineering | Volume 198 | Number 4 | April 2024 | Pages 853-897
Research Article | doi.org/10.1080/00295639.2023.2214488
Articles are hosted by Taylor and Francis Online.
The development of higher-order method of characteristics (MOC) discretizations has become of great interest to improve the performance of solvers based on the standard Stepwise Constant (SC) MOC approximation. Many codes nowadays implement a Stepwise Linear (SL) volume flux approximation or diamond differencing schemes. In the multigroup lattice solver TDT of the industrial code APOLLO3®, developed at CEA, a Linear Surface (LS) scheme was implemented. In this method, the flux is reconstructed from a linear interpolation made from surface values, therefore ensuring a similar spatial linear development but with a lower computational cost than the volume-based approximations. However, the LS-MOC scheme can conserve only the constant spatial moment of the flux. To overcome this limitation, in this paper we propose an improved version of the LS scheme called LS- able to preserve the linear spatial moments of the flux. Compared to the other high-order volume-based approximations, the LS- scheme also preserves flux surface moments, which guarantees higher accuracy. Moreover, our scheme has a lower memory footprint because it does not require the storage of response matrices that are dependent on region, group, and anisotropy order. Tests carried out on severe rodded assembly cases show the superior performance of the proposed method with respect to not only the classic SC or LS MOC scheme but also the SL scheme.