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Division Spotlight
Reactor Physics
The division's objectives are to promote the advancement of knowledge and understanding of the fundamental physical phenomena characterizing nuclear reactors and other nuclear systems. The division encourages research and disseminates information through meetings and publications. Areas of technical interest include nuclear data, particle interactions and transport, reactor and nuclear systems analysis, methods, design, validation and operating experience and standards. The Wigner Award heads the awards program.
Meeting Spotlight
International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2025)
April 27–30, 2025
Denver, CO|The Westin Denver Downtown
Standards Program
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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Latest News
Dragonfly, a Pu-fueled drone heading to Titan, gets key NASA approval
Curiosity landed on Mars sporting a radioisotope thermoelectric generator (RTG) in 2012, and a second NASA rover, Perseverance, landed in 2021. Both are still rolling across the red planet in the name of science. Another exploratory craft with a similar plutonium-238–fueled RTG but a very different mission—to fly between multiple test sites on Titan, Saturn’s largest moon—recently got one step closer to deployment.
On April 25, NASA and the Johns Hopkins University Applied Physics Laboratory (APL) announced that the Dragonfly mission to Saturn’s icy moon passed its critical design review. “Passing this mission milestone means that Dragonfly’s mission design, fabrication, integration, and test plans are all approved, and the mission can now turn its attention to the construction of the spacecraft itself,” according to NASA.
E. E. Bende
Nuclear Technology | Volume 131 | Number 3 | September 2000 | Pages 279-296
Technical Paper | Fission Reactors | doi.org/10.13182/NT00-A3117
Articles are hosted by Taylor and Francis Online.
This work presents the temperature reactivity effects occurring in pebbles of a high-temperature reactor fueled with reactor-grade plutonium, without any additional resonance absorbers. Burnup calculations are performed for pebbles loaded with various amounts of plutonium per pebble. During burnup, branching calculations are carried out to calculate k as a function of the uniform temperature. For a high plutonium mass per pebble and low burnup values, k decreases with uniform temperature, which indicates a negative uniform temperature coefficient of reactivity (UTC). However, for a low plutonium mass per pebble, as well as for a high plutonium mass per pebble in combination with high burnup, k is maximal at a particular uniform temperature. Below this temperature, the UTC is positive, while above this temperature it is negative. Branching calculations with only a varying moderator temperature show almost the same behavior, which indicates that the contribution of the fuel temperature plays a minor role for the mentioned effect. To understand the reactivity effect, the moderator temperature coefficient (MTC) is investigated by two methods. In the first method, changes in reaction rates of individual nuclides and their corresponding contributions to the MTC are calculated, whereas in the second method the four-factor formula has been used. For the fresh fuel cases, the positive coefficient at low temperature is due to a positive coefficient for the thermal utilization factor. For high moderator temperatures, the coefficient for the resonance escape probability renders the MTC negative. This trend is basically caused by the shift of the high-energy tail of the Maxwell-spectrum toward the 1-eV resonance of 240Pu, and toward the resonances of 241Pu, which leads to an increase of the capture-to-fission ratio.
