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The evaluated spectroscopic data are presented for known nuclides of mass 228 (Ac, At, Fr, Np, Pa, Pu, Ra, Rn, Th, and U). Excited states in {sup 228}At, {sup 228}Rn, {sup 228}Fr, {sup 228}Np, and {sup 228}Pu have not been identified as yet. Significant amounts of new data have been added since the last evaluation of A=228 nuclides. This work supersedes earlier full evaluations of A=228 published by 1997Ar08.
The nucleus {sup 235m}U is an isomer with extremely low excitation energy (76.8 eV) and decays dominantly through the internal conversion (IC) process. Because outer-shell electrons are involved in the IC process, the decay constant of {sup 235m}U depends on its chemical environment. We plan to study the deexcitation process of {sup 235m}U by measuring the energy spectra of IC electrons in addition to the decay constants for various chemical forms. In this paper, the preparation method of {sup 235m}U samples from {sup 239}Pu by using alpha-recoil energy is reported. A Collection Apparatus for Recoil Products was fabricated, and then collection efficiencies under various conditions were determined by collecting {sup 224}Ra recoiling out of {sup 228}Th electrodeposited and precipitated sources. The pressure in the apparatus (vacuum or 1 atm of N{sub 2} gas) affected the variations of the collection efficiencies depending on the negative voltage applied to the collector. The maximum values of the collection efficiencies were mainly affected by the thickness of the {sup 228}Th sources. From these results, the suitable conditions of the {sup 239}Pu sources for preparation of {sup 235m}U were determined. In addition, dissolution efficiencies were determined by washing collected {sup 224}Ra with solutions. When {sup 224}Ra was collected in 1 atm of N{sub 2} gas and dissolved with polar solutions such as water, the dissolution efficiencies were nearly 100%. The method of rapid dissolution of recoil products would be applicable to rapid preparation of short-lived {sup 235m}U samples for various chemical forms.
An Evaluation and Screening (E and S) study of nuclear fuel cycle options was recently conducted for the U.S. Department of Energy to identify promising fuel cycle options with the potential for achieving substantial improvements compared to the current nuclear fuel cycle in the U.S. This study considered the entire fuel cycle, i.e., the complete nuclear energy system from mining to disposal including both once-through and recycle fuel cycles. The E and S study considered performance at steady-state when evaluating the potential benefits and challenges to achieving that eventual end state. Based on the steady-state findings from the E and S, a set of four fuel cycle options (FCOs) were identified as most promising, in terms of offering the most benefits compared to the current cycle. These FCOs have natural uranium (or existing stocks of uranium such as depleted uranium) as the makeup feed sent to the fast reactor (FR) fleet combined with two dimensions. The first dimension is whether the FR is a single-stage (produces just enough fuel resources to sustain operation and growth of the FR fleet) or a two-stage (produces additional fuel resources to also sustain a companion fleet of thermal reactors) fuel cycle. In all four cases, all of the uranium is continuously recycled. The second dimension is whether only the plutonium is co-extracted and recycled with the uranium (with minor actinides disposed as waste) or all transuranic elements are co-extracted and recycled. The four most promising options are: 1) single-stage FR recycling of U/Pu (EG23), 2) recycling of U/TRU in single-stage FR (EG24), 3) recycling of U/Pu in two-stage FR/thermal reactors (EG29), and 4) recycling of U/TRU in two-stage FR/thermal reactors (EG30). (authors)