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Division Spotlight
Operations & Power
Members focus on the dissemination of knowledge and information in the area of power reactors with particular application to the production of electric power and process heat. The division sponsors meetings on the coverage of applied nuclear science and engineering as related to power plants, non-power reactors, and other nuclear facilities. It encourages and assists with the dissemination of knowledge pertinent to the safe and efficient operation of nuclear facilities through professional staff development, information exchange, and supporting the generation of viable solutions to current issues.
Meeting Spotlight
2024 ANS Annual Conference
June 16–19, 2024
Las Vegas, NV|Mandalay Bay Resort and Casino
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
Can hydrogen be the transportation fuel in an otherwise nuclear economy?
Let’s face it: The global economy should be powered primarily by nuclear power. And it probably will by the end of this century, with a still-significant assist from renewables and hydro. Once nuclear systems are dominant, the costs come down to where gas is now; and when carbon emissions are reduced to a small portion of their present state, it will become obvious that most other sources are only good in niche settings. I mean, why use small modular reactors to load-follow when they can just produce that power instead of buffering it?
Eva E. Davidson, William R. Martin
Nuclear Science and Engineering | Volume 187 | Number 1 | July 2017 | Pages 1-26
Technical Paper | doi.org/10.1080/00295639.2017.1294931
Articles are hosted by Taylor and Francis Online.
Current Monte Carlo codes use one of three models: (1) the asymptotic scattering model, (2) the free gas scattering model, or (3) the S(α,β) model, depending on the neutron energy and the specific Monte Carlo code. This paper addresses the consequences of using the free gas scattering model, which assumes that the neutron interacts with atoms in thermal motion in a monatomic gas in thermal equilibrium at material temperature T. Most importantly, the free gas model assumes the scattering cross section is constant over the neutron energy range, which is usually a good approximation for light nuclei, but not for heavy nuclei, where the scattering cross section may have several resonances in the epithermal region. Several researchers in the field have shown that the exact resonance scattering model is temperature dependent, and neglecting the resonances in the lower epithermal range can underpredict resonance absorption due to the upscattering phenomenon mentioned above, leading to an overprediction of keff by several hundred pcm. Existing methods to address this issue involve changing the neutron weights or implementing an extra rejection scheme in the free gas sampling scheme, and these all involve performing the collision analysis in the center-of-mass (CM) frame, followed by a conversion back to the laboratory frame to continue the random walk of the neutron.
The goal of this paper was to develop a sampling methodology that (1) accounted for the energy-dependent scattering cross sections in the collision analysis and (2) was performed in the laboratory frame, avoiding the conversion to the CM frame. The energy dependence of the scattering cross section was modeled with even-ordered polynomials (second and fourth order) to approximate the scattering cross section in Blackshaw’s equations for the moments of the differential scattering probability distribution functions. These moments were used to sample the outgoing neutron speed and angle in the laboratory frame on the fly during the random walk of the neutron. Results for criticality studies on fuel pin and fuel assembly calculations using methods developed in this paper showed very close comparison to results using the reference Doppler-broadened rejection correction scheme.