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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.
Luca Fiorito, Matteo Zanetti, Federico Grimaldi, Gert van den Eynde
Nuclear Science and Engineering | Volume 199 | Number 1 | April 2025 | Pages S56-S72
Review Article | doi.org/10.1080/00295639.2024.2353987
Articles are hosted by Taylor and Francis Online.
Safety analyses of MYRRHA require calculating the reactor temperature feedback coefficients of reactivity associated with power operation. Within this framework, a significant emphasis is put on the quantification of the reactivity coefficient uncertainty, which takes into account different uncertainty sources. This work reports the investigation of the fuel Doppler coefficient of reactivity of MYRRHA implemented with the Serpent 2 Monte Carlo particle transport code. Nuclear data and the MYRRHA mixed-oxide (MOX) fuel composition are selected as major sources of uncertainties, and their impact on the Doppler coefficient is assessed with a stochastic sampling approach. Nuclear data covariance matrices are taken from the JEFF-3.3 evaluated library and propagated with the SANDY code.
Uncertainties of the fuel composition are derived from declared records for MOX fuel assemblies irradiated in a pressurized water reactor/boiling water reactor. The contribution of the aleatoric Monte Carlo uncertainty could be removed from the stochastic uncertainty estimate of the Doppler coefficient by using a methodology based on conditional estimators. This technique has proved to be tremendously advantageous to quantify the uncertainty of reactivity feedback coefficients using Monte Carlo codes, overcoming some of the limitations associated with sensitivity-based uncertainty propagation methods. The uncertainties of the MYRRHA Doppler constant KD, considering the variability of nuclear data (only cross sections) and MOX fuel compositions, are, respectively, 3.0% and 1.3%, with a negligible dependence on the considered fuel temperature. The largest nuclear data uncertainty contributions comes from 238U and 239,240Pu, while the impact of the Pb and Bi uncertainties is only marginal.