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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.
Patrick F. O’Rourke, Anil K. Prinja, Scott D. Ramsey
Nuclear Science and Engineering | Volume 199 | Number 1 | April 2025 | Pages S180-S200
Research Article | doi.org/10.1080/00295639.2024.2439227
Articles are hosted by Taylor and Francis Online.
In this report, we study several aspects of the root spectrum of the coupled assembly probability of initiation equations to bolster confidence in the results of the companion paper, A. K. Prinja, P. F. O’Rourke, and S. D. Ramsey, “Probability of Initiation in Coupled Multiplying Assemblies.” We apply Bernstein’s Theorem to develop analytical expressions for the number of distinct nontrivial roots for two and three coupled assemblies and make inferences that the behavior holds in general. This result provides a benchmark number for the expected number of roots to be obtained when calculating the entire root spectrum. We employ a numerical method, the Homotopy Continuation Method (HCM), to obtain the entire root spectrum. We use the HCM to study parametric behavior of the root spectrum for subcritical and supercritical systems and compare with the Newton-Raphson Method (NRM) result, which provides only a single solution but is computationally favorable. We show that indeed the NRM and HCM agree (for a single root), and we further perform a stability analysis on the entire spectrum to show that the NRM result is the only stable root in the spectrum for the entire range of system criticalities. The results are demonstrated for systems consisting of two and four coupled assemblies.