The branching ratio of core-valence transitions in x-ray absorption spectroscopy and electron energy loss spectroscopy is linearly related to the expectation value of the spin-orbit operator of the valence states. Here, we analyze the measured branching ratio of the N{sub 4,5} edges acquired by electron energy-loss spectroscopy in a transmission electron microscope, and synchrotron-radiation-based x-ray absorption. Results show that the spin-orbit sum rule can be applied to actinide 5f states, where the accuracy can be increased using the correction term obtained from atomic many-electron calculations.

The principal research efforts for this Continuation Period are the preparation and submittal to DOE of the final report for Phase I of this project, the preparation and submittal of a technical paper for consideration for publication reporting the results of this project, and the evaluation by Pruet Production Co. to continue into Phase II of this project.

Safe disposal of the nation's nuclear waste in a geological repository involves unique scientific and engineering challenges owing to the very long-lived radioactivity of the waste. The repository must retain a variety of radionuclides that have vastly different chemical characters for several thousand years. Most of the radioactivity that will be housed in the proposed repository at Yucca Mountain will be associated with spent nuclear fuel, much of which is derived from commercial reactors. DOE is custodian of approximately 8000 tons of spent nuclear fuel that is also intended for eventual disposal in a geological repository. Unlike the spent fuel from commercial reactors, the DOE fuel is diverse in composition with more than 250 varieties. Safe disposal of spent fuel requires a detailed knowledge of its long-term behavior under repository conditions, as well as the fate of radionuclides released from the spent fuel as waste containers are breached.