Radiolytic and thermal process relevant to dry storage of spent nuclear fuels. 1998 annual progress report Page: 2 of 3
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Radiolytic and Thermal Process Relevant to Dry Storage
of Spent Nuclear Fuels
Steven C. Marschman, Pacific Northwest National Laboratory
Peter E. Haustein, Brookhaven National Laboratory
James P. Cowin, Pacific Northwest National Laboratory
Thomas M. Orlando, Pacific Northwest National Laboratory
Theodore E. Madey, Rutgers, the State University of New Jersey
This project involves basic research in chemistry and physics aimed at providing information pertinent
to the safe long-term dry storage of spent nuclear fuel (SNF), thousands of tons of which remain in
water storage across the DOE complex. The Hanford Site K-Basins alone hold 2300 tons of spent
fuel, much of it severely corroded, and similar situations exist at Savannah River and Idaho National
Engineering and Environmental Laboratory. The DOE plans to remove this fuel and seal it in overpack
canisters for "dry" interim storage for up to 75 years while awaiting permanent disposition. Chemically-
bound water will remain in this fuel even following proposed drying steps, leading to possible long-
term corrosion of the containers and/or fuel rods themselves, generation of H2 and 02 gas via radiolysis
(which could lead to deflagration or detonation), and reactions of pyrophoric uranium hydrides. No
thoroughly tested model is currently available to predict fuel behavior during pre-processing,
processing, or storage. In a collaboration between Rutgers University, Pacific Northwest National
Laboratory, and Brookhaven National Laboratory, we are studying the radiolytic reaction, drying
processes, and corrosion behavior of actual SNF materials, and of pure and mixed-phase samples.
We propose to determine what is omitted from current models: radiolysis of water adsorbed on or in
hydrates or hydroxides, thermodynamics of interfacial phases, and kinetics of drying. A model will
be developed and tested against actual fuel rod behavior to insure validity and applicability to the
problems associated with developing dry storage strategies for DOE-owned SNF.
Research Progress and Implications
This report summarizes work after eight months of a three-year project.
Relevant oxide surfaces of U02, ZrO2, and Al203 have been prepared and characterized by x-ray
photoelectron spectroscopy. Measurements are being made of the desorption of water from these
surfaces, using accurate thermal desorption methods to elucidate the effects of temperature on the
surface-water interaction. Interfacial nuclear decay and radiolysis processes that either affect the
structural integrity of relevant materials or evolve flammable gases have been studied on Al203 and
ZrO2 surfaces using intense radioactive sources with radiochemical tracer techniques. Processes for
generating thin (0.1-mm) uranium oxide films have been developed using three different processes:
metal sputtering; electrodeless plating; and thermal treatment of uranyl nitrate deposited from solution
on tungsten. Such films have been characterized by electron microscopy, revealing in partially-nitrated
specimens "shrink cracks" that may have profound implications for their chemical reactivity. A
promising computational model of the effects of particle size and sample thickness has been developed
and substantiated with experiments on MgO and TiO2 powders. This will be applied to the analogous
problems for SNF materials.
The breakdown of zirconia films (important to the integrity of Zr-alloy fuel-rod cladding) under
extreme radiation conditions has been systematically studied using low-energy electron and photon
bombardment of well-characterized ZrO2 surfaces. These studies have clarified the mechanism of
oxygen removal from such surfaces, which involves the ionization of shallow metal cation core
EMSP Project Summaries
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Marschman, S. C.; Cowin, J. P.; Orlando, T. M.; Haustein, P. E. & Madey, T. E. Radiolytic and thermal process relevant to dry storage of spent nuclear fuels. 1998 annual progress report, report, June 1998; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc620773/m1/2/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.