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Division Spotlight
Thermal Hydraulics
The division provides a forum for focused technical dialogue on thermal hydraulic technology in the nuclear industry. Specifically, this will include heat transfer and fluid mechanics involved in the utilization of nuclear energy. It is intended to attract the highest quality of theoretical and experimental work to ANS, including research on basic phenomena and application to nuclear system design.
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ANS Student Conference 2025
April 3–5, 2025
Albuquerque, NM|The University of New Mexico
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The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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General Kenneth Nichols and the Manhattan Project
Nichols
The Oak Ridger has published the latest in a series of articles about General Kenneth D. Nichols, the Manhattan Project, and the 1954 Atomic Energy Act. The series has been produced by Nichols’ grandniece Barbara Rogers Scollin and Oak Ridge (Tenn.) city historian David Ray Smith. Gen. Nichols (1907–2000) was the district engineer for the Manhattan Engineer District during the Manhattan Project.
As Smith and Scollin explain, Nichols “had supervision of the research and development connected with, and the design, construction, and operation of, all plants required to produce plutonium-239 and uranium-235, including the construction of the towns of Oak Ridge, Tennessee, and Richland, Washington. The responsibility of his position was massive as he oversaw a workforce of both military and civilian personnel of approximately 125,000; his Oak Ridge office became the center of the wartime atomic energy’s activities.”
Sapna Singh, Garima Singal, A. K. Nayak
Nuclear Science and Engineering | Volume 187 | Number 2 | August 2017 | Pages 185-201
Technical Paper | doi.org/10.1080/00295639.2017.1307048
Articles are hosted by Taylor and Francis Online.
Natural Circulation Boiling Water Reactors (BWRs) are susceptible to boiling two-phase flow instabilities under certain conditions, which can lead to flow oscillations in the reactors. These oscillations could be in-phase or out-of-phase in nature depending on the geometry and operating conditions of the system.
This paper reports on a study on the effect of both thermal hydraulics as well as neutron kinetics on the characteristics of boiling two-phase natural circulation flow instabilities in a pressure tube type natural circulation BWR. RELAP5/MOD3.2 code has been used to simulate the natural circulation behavior in multiple channels of the reactor. Before applying the RELAP5 model for simulation of natural circulation in this reactor, the code was benchmarked with the experiment conducted in a multichannel boiling natural circulation loop, having geometry similar to this reactor. The results showed that the RELAP5 model is able to capture the boiling induced-flow instabilities. Then the model was applied to simulate the reactor behavior. The prediction showed that the reactor could experience both Type-I and Type-II density wave oscillations depending on the channel inlet subcooling and channel power. Unlike Type-II instability wherein clear cut outs of phase oscillations among multiple channels were observed, in Type-I instability it was observed that mixed mode oscillations could be present, especially at low subcooling. The phase difference among the channels were found to change with time in Type-I instability. These are completely new findings with regard to characteristics of boiling two-phase natural circulation.
The fuel in this reactor is a combination of (Th-233U)O2 and (Th-Pu)O2, which is different from conventional BWRs. Also, the coolant (light water) is present in different pressure tubes which are physically separated from moderator (heavy water). The effect of neutronic feedback due to this fuel and geometrical configuration on characteristics of Type-I and Type-II instabilities has not been investigated before. In view of this, a systematic investigation was done to study the effect of neutronic feedback on Type-I and Type-II oscillations observed in this reactor. The simulation showed that the threshold power for both Type-I and Type-II instability slightly stabilizes with introduction of neutronic feedback. Since the magnitude of void reactivity feedback is very small in the present fuel composition, the stability boundary was only slightly altered with the introduction of neutronic feedback. Regarding the oscillation characteristics, it was found that change in magnitude of void reactivity has almost no effect on Type-I oscillations whereas the Type-II oscillations get stabilized when void reactivity magnitude was increased. This kind of effect due to void reactivity feedback is in contrast to findings based on conventional BWR and is an important finding of the present study.
