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Conference Spotlight
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.
M. P. Sharma, A. K. Nayak
Nuclear Science and Engineering | Volume 184 | Number 2 | October 2016 | Pages 280-291
Technical Paper | doi.org/10.13182/NSE15-112
Articles are hosted by Taylor and Francis Online.
The Advanced Heavy Water Reactor (AHWR) is a vertical pressure tube–type, heavy water–moderated and boiling light water–cooled natural circulation–based reactor. The fuel bundle of an AHWR contains 54 fuel rods arranged in three concentric rings of 12, 18, and 24 fuel rods. This fuel bundle is divided into a number of imaginary interacting flow passages called subchannels. The transition from single-phase to two-phase flow occurs in a reactor rod bundle with an increase in power. Two-phase flow regimes like bubbly, slug/churn, and annular flow are normally encountered in a reactor rod bundle. Prediction of the thermal margin of the reactor necessitates the determination of the turbulent-mixing rate of the coolant among these subchannels under these flow regimes. Thus, it is vital to evaluate turbulent mixing between the subchannels of an AHWR rod bundle.
In this paper, experiments were carried out to determine the two-phase turbulent-mixing rate in different flow regimes in the simulated subchannels of the reactor. The size of the rod and the pitch in the test were the same as those of an actual rod bundle in the prototype. Three subchannels are considered in 1/12th of the cross section of the rod bundle. Water and air were used as the working fluid, and the turbulent-mixing tests were carried out at atmospheric conditions without addition of heat. The void fraction was varied from 0 to 0.8 under various ranges of superficial liquid velocity. The turbulent-mixing rate was experimentally determined by adding tracer fluid in one subchannel and measuring its concentration in other subchannels at the end of the flow path. The test data were compared with existing models in the literature. It was found that none of the models could predict the measured turbulent-mixing rate in the rod bundle of the reactor.