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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.
Vikas Pandey, Suneet Singh
Nuclear Science and Engineering | Volume 188 | Number 2 | November 2017 | Pages 187-197
Technical Paper | doi.org/10.1080/00295639.2017.1350003
Articles are hosted by Taylor and Francis Online.
The nonlinear stability analysis of an advanced heavy water reactor (AHWR) is performed to investigate global stability. The global stability perspective predicts the exact stability boundary of the system, which is valid for small as well as large disturbances in the system. Recently, the local or linear stability boundary and bifurcation of limit cycles has been discussed for an AHWR. However, the studies were not sufficient to predict global stability of the system. In this work, advanced bifurcation analysis is carried out for an AHWR, which unfolds multistable or unstable states. The region of multistability is observed due to the presence of steady states and multiple limit cycles. The global stability boundary is marginally away from the local stability boundary, the region beyond which the global stability boundary is safe for operation due to the nonexistence of nonlinear phenomena, such as limit cycles. The local stability boundary is basically a Hopf bifurcation boundary as limit cycles (i.e., nonlinear phenomena) emerge from these points. Subcritical or supercritical Hopf bifurcations excite unstable limit cycles (ULCs) or stable limit cycles (SLCs), respectively, and these limit cycles end on the global stability boundary. The subcritical Hopf bifurcation is considered as hard or dangerous bifurcation due to the presence of ULCs in the linearly stable region, which gains stability on the global stability boundary and in which SLCs surround ULCs. Therefore, a region of bistability between the local and global stability boundary is present for subcritical Hopf. The supercritical Hopf is generally considered as the soft and safe bifurcation because of SLCs in the linearly unstable region. Due to this fact, it is assumed that in the supercritical Hopf region the global and local stability boundaries are the same. However, in this work ULCs in the linearly stable region for supercritical Hopf bifurcation are observed along with SLCs, which is an uncommon phenomenon in nuclear reactors. The presence of ULCs surrounding SLCs are observed both in the stable and unstable side on the parameter plane for supercritical Hopf. For the safe operation of a nuclear reactor, identification of the region of global stability is of paramount interest.
