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Conference Spotlight
Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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Ho Nieh nominated to the NRC
Nieh
President Trump recently nominated Ho Nieh for the role of commissioner in the Nuclear Regulatory Commission through the remainder of a term that will expire June 30, 2029.
Nieh has been the vice president of regulatory affairs at Southern Nuclear since 2021, though he is currently working as a loaned executive at the Institute of Nuclear Power Operations, where he has been for more than a year.
Nieh’s experience: Nieh started his career at the Knolls Atomic Power Laboratory, where he worked primarily as a nuclear plant engineer and contributed as a civilian instructor in the U.S. Navy’s Nuclear Power Program.
From there, he joined the NRC in 1997 as a project engineer. In more than 19 years of service at the organization, he served in a variety of key leadership roles, including division director of Reactor Projects, division director of Inspection and Regional Support, and director of the Office of Nuclear Reactor Regulation.
Maximiliano Dalinger, William Walters
Nuclear Science and Engineering | Volume 199 | Number 1 | April 2025 | Pages S754-S764
Research Article | doi.org/10.1080/00295639.2024.2328944
Articles are hosted by Taylor and Francis Online.
Monte Carlo codes are the most accurate way to solve the neutronics in a reactor core but can be computationally expensive, especially for when feedback effects are considered or for transient calculations. In this paper, we use the fission matrix (FM) method to perform static and transient calculations with point-kinetics equations and a quasi-static model for an adiabatic transient with feedback. This was applied to a three-dimensional model of the Transient Reactor Test Facility (TREAT) experimental reactor using the Monte Carlo code Serpent for reference calculations and to generate fission matrix databases (FMDBs). In previous works, FMDBs were generated with uniform fuel temperature profiles. Here, we analyze the use of FMDBs with nonuniform temperature profiles, for static and transient calculations. For static calculations, comparison between Serpent and the FM method using nonuniform and uniform FMDBs showed maximum differences in multiplication factors of 57.0 and 77.9 pcm, respectively. For the fission source distribution, comparisons showed maximum root-mean-square differences of 1.10% and 4.89% for nonuniform and uniform FMDBs, respectively. Similar results were obtained when using homogenized databases. Therefore, using nonuniform FMDBs produces a better approximation than uniform databases. For transient calculations, comparisons between both database sets showed differences of 0.9% and −1.8% for the peak and final total power.
