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2025 ANS Winter Conference & Expo
November 9–12, 2025
Washington, DC|Washington Hilton
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TVA nominees promise to support advanced reactor development
Four nominees to serve on the Tennessee Valley Authority Board of Directors told the Senate Environment and Public Works Committee that they support the build-out of new advanced nuclear reactors to meet the increased energy demand being shouldered by the country’s largest public utility.
Michael Y. Hua, Jesson D. Hutchinson, George E. McKenzie, Tony H. Shin, Shaun D. Clarke, Sara A. Pozzi
Nuclear Science and Engineering | Volume 194 | Number 1 | January 2020 | Pages 56-68
Technical Paper | doi.org/10.1080/00295639.2019.1654327
Articles are hosted by Taylor and Francis Online.
Rossi-alpha measurements of fissionable assemblies are used to estimate the prompt neutron decay constant α. Reactivity can be inferred from α if the values of the neutron generation time and effective delayed neutron fraction are assumed. If multiple measurements are performed on an assembly near delayed critical, one can determine α at delayed critical and directly infer reactivity (without needing to assume values for the neutron generation time or effective delayed neutron fraction). Previous works have demonstrated that two-exponential fits for Rossi-alpha measurements of reflected assemblies have better fit metrics than those of one-exponential fits; however, the two-exponential probability density function that is needed to obtain α from the fit parameters has not been derived. This paper derives the two-exponential fit based on a two-region point kinetics model for Rossi-alpha measurements of reflected assemblies, a generalization of the current, one-region model (one-exponential fit). The new model is validated for shielded assemblies, a special case of reflected assemblies where the reflector-to-core leakage is negligibly small. The validation is performed using shielded, fissionable assemblies (highly enriched uranium with keff ≈ 0.95 and weapons-grade plutonium with keff > 0.77). The results show that the two-exponential model can (1) predict the constant α within two standard deviations, and (2) deconvolve α and the time a neutron spends in the reflector region, neither of which is possible with the one-exponential model.