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Growth beyond megawatts
Hash Hashemianpresident@ans.org
When talking about growth in the nuclear sector, there can be a somewhat myopic focus on increasing capacity from year to year. Certainly, we all feel a degree of excitement when new projects are announced, and such announcements are undoubtedly a reflection of growth in the field, but it’s important to keep in mind that growth in nuclear has many metrics and takes many forms.
Nuclear growth—beyond megawatts—also takes the form of increasing international engagement. That engagement looks like newcomer countries building their nuclear sectors for the first time. It also looks like countries with established nuclear sectors deepening their connections and collaborations. This is one of the reasons I have been focused throughout my presidency on bringing more international members and organizations into the fold of the American Nuclear Society.
Dan Gabriel Cacuci
Nuclear Science and Engineering | Volume 193 | Number 7 | July 2019 | Pages 681-721
Technical Paper | doi.org/10.1080/00295639.2018.1564504
Articles are hosted by Taylor and Francis Online.
For over 60 years, the Roussopoulos and Schwinger functionals have been used in many works and textbooks under the assumption that they provide “second-order accurate” trial functions for the forward and adjoint fluxes when computing reaction rates and/or particle detector responses in source-driven nuclear systems. The Schwinger functional has been employed as a particularly useful form of the Roussopoulos functional for systems in which the forward and adjoint particle fluxes were normalized. When using these functionals, however, the expressions for the approximate fluxes were postulated arbitrarily while the system parameters were unrealistically assumed to be perfectly well known. This work revisits the Roussopoulos and Schwinger functionals within the realistic practical context of imprecisely known model parameters, including imprecisely known cross sections, number densities, fission spectra, and forward and adjoint sources. By applying the Second-Order Adjoint Sensitivity Analysis (2nd-ASAM) methodology, this work shows that the first-order sensitivities of the Roussopoulos and Schwinger functionals to model parameters are not identically zero. This fact implies that neither the Roussopoulos nor the Schwinger functionals are accurate to second order in parameter variations/uncertainties, which implies, in turn, that these functionals are not accurate to second order variations in the flux when such flux-variations are caused by imprecisely known model parameters. Furthermore, the 2nd-ASAM methodology applied in this work also provides exactly and efficiently all of the second-order sensitivities of the Roussopoulos and Schwinger functionals to the imprecisely known model parameters. The new results presented in this work place in the correct light the results published hitherto in works that have used the Roussopoulos and Schwinger functionals while also indicating the correct path for future possible uses of these functionals for performing sensitivity and uncertainty analyses of both forward and inverse problems in nuclear systems.
