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2025 ANS Winter Conference & Expo
November 9–12, 2025
Washington, DC|Washington Hilton
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Latest News
Senate EPW Committee to hold Nieh nomination hearing
Nieh
The Senate Environment and Public Works Committee will hold a nomination hearing Wednesday for Ho Nieh, President Donald Trump’s nominee to serve as commission at the Nuclear Regulatory Commission.
Trump nominated Nieh on July 30 to serve as NRC commissioner the remainder of a term that will expire June 30, 2029, as Nuclear NewsWire previously reported.
Nieh has been vice president of regulatory affairs at Southern Nuclear since 2021, though since June 2024 he has been at the Institute of Nuclear Power Operations as a loaned executive.
A return to the NRC: If confirmed by the Senate, Nieh would be returning to the NRC after three previous stints totaling nearly 20 years.
M. Hursin, B. Collins, Y. Xu, T. Downar
Nuclear Science and Engineering | Volume 176 | Number 2 | February 2014 | Pages 186-200
Technical Paper | doi.org/10.13182/NSE12-4
Articles are hosted by Taylor and Francis Online.
During the last several years, a class of algorithms has been developed based on two-dimensional–one-dimensional (2D-1D) decomposition of the reactor transport problem. The current 2D-1D algorithm implemented in the DeCART (Deterministic Core Analysis based on Ray Tracing) code solves a set of coupled 2D planar transport and 1D axial diffusion equations. This method has been successfully applied to several light water reactor analysis problems. However, applications with strong axial heterogeneities have exposed the limitations of the current diffusion solvers used for the axial solution. The work reported in this paper is the implementation of a discrete ordinates (Sn)-based axial solver in DeCART. An Sn solver is chosen to preserve the consistency of the angular discretization between the radial method of characteristics and axial solvers. This paper presents the derivation of the nodal expansion method (NEM)-Sn equations and its implementation in DeCART. The subplane spatial refinement method is introduced to reduce the computational cost and improve the accuracy of the calculations. The NEM-Sn axial solver is tested using the C5G7 benchmark. The DeCART results with the axial diffusion solver shows keff errors of approximately −95, −74, and −110 pcm for the unrodded configuration, rodded configuration A, and rodded configuration B, respectively. These errors decrease to approximately −40, −11, and −12 pcm by using the NEM-Sn solver. In terms of pin power distribution, the use of the NEM-Sn solver has a small effect, except for the heavily rodded configuration. The implementation of the subplane scheme makes it possible to maintain a coarse axial mesh and therefore to reduce the computational cost of the three-dimensional calculations without reducing the accuracy of the solution.
