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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.
Masahiro Fukushima, Masaki Andoh, Yasunobu Nagaya
Nuclear Science and Engineering | Volume 199 | Number 6 | June 2025 | Pages 1029-1043
Note | doi.org/10.1080/00295639.2024.2405668
Articles are hosted by Taylor and Francis Online.
A series of simulated experiments were conducted at the fast critical assembly (FCA) of the Japan Atomic Energy Agency to simulate a light water reactor core with a tight lattice cell containing highly enriched mixed-oxide fuel with a fissile plutonium (Pu) ratio >15%. The prediction accuracy of the neutron computation codes and nuclear data libraries in a wide range of neutron spectra was evaluated by constructing three experimental configurations of the FCA-XXII-1 assembly with different void fractions (45%, 65%, and 95%) of the moderator material (foamed polystyrene). The hydrogen-to–nuclear fuel atomic ratio was systematically varied from 0.1 to 0.8. In a previous paper, we reported the criticality and reactivity worths measured in these experiments.
This technical note provides the experimental results for the central reaction rate ratios and fission distributions as follows. The fission rate ratios of uranium (U) (238U) and 239Pu relative to 235U were measured at the core centers using three calibrated fission chambers, and the 238U capture reaction rate ratio relative to 235U fission was measured using depleted U foils. The reaction rate distributions were also obtained by traversing four micro fission chambers of highly enriched U, natural U, Pu, and neptunium through each core region in the radial and axial directions. The experimental analyses were performed using detailed models of the Monte Carlo code MVP3 with the Japanese evaluated nuclear data library of JENDL-4.0. Most calculation results agreed well with the experiments, whereas those for the fission rate ratio of 239Pu to 235U were underestimated by up to 6% with the softening neutron spectrum.