Chemical Decomposition of High-Level Nuclear Waste Storage/Disposal Glasses Under Irradiation Page: 2 of 3
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CHEMICAL DECOMPOSITION OF HIGH-LEVEL NUCLEAR WASTE
STORAGE/DISPOSAL GLASSES UNDER IRRADIATION
U.S. Dept. of Energy Environmental Management Science Program
Project Summary/Progress Report
David L. Griscom, Principal Investigator
Phone: (202) 404-7087
FAX: (202) 767-5792
e-mail: griscom@nrl.navy.mil
RESEARCH OBJECTIVE
The objective of this project is to employ the technique of electron spin resonance (ESR), in
conjunction with other experimental methods, to study radiation-induced decomposition of vitreous
compositions proposed for immobilization/disposal of high-level nuclear wastes (HLW) or excess weapons
plutonium. ESR is capable of identifying, even at the parts-per-million level, displaced atoms, ruptured
bonds, and free radicals created by radiation in such glassy forms. For example, one of the scientific goals
is to search for ESR-detectable superoxide (02) and ozonide (O-) ions, which could be precursors of
radiation-induced oxygen gas bubbles reported by other investigators via the disproportionation reaction, 202
O2 + 02. The fundamental understandings obtained in this study will enable reliable predictions of the
long-term effects of a and P decays of the immobilized radionuclides on the chemical integrity of HLW
glasses.
RESEARCH PROGRESS AND IMPLICATIONS
This report summarizes the results of a 30-month effort performed under a 3-year research award.
Four categories of materials were studied: (A) several actual and proposed HLW glass compositions
fabricated at Savannah River Technology Center (SRTC), (B) several high-iron phosphate glasses fabricated
at the University of Missouri-Rolla (UMR), (C) an iron-free boro-aluminosilicate model HLW glass
subjected to y rays (to simulate P-decay effects) and to implantation by 160-keV He+ ions (to simulate a-
decay damage), and (D) well-dated geological glasses damaged by a decays of trace amounts of contained
238U and 232Th over a period of 65 million years. Among materials A were two samples of Defense Waste
Processing Facility (DWPF) borosilicate glasses modeling compositions currently being used to vitrify HLW
at SRTC. The ESR spectra recorded for the unirradiated DWPF-glass simulants were attributable to Fe3+ ions
and/or precipitated ferrites. The sole effect of a 30-MGy y irradiation (1 Gy = 100 rad) was to change the
Fe3+ concentration of these glasses by a statistically insignificant factor (0.987 0.050). No induced defect
centers were measurable by ESR, possibly due to a suppression effect of the Fe3+ ions. (N.B. The presence
or absence of radiolytic 02 cannot be directly determined by ESR.)
Another category-A material, an iron phosphate glass containing Li20 and CeO2, displayed a much
larger y-radiation ESR response than did the DWPF glass. Specifically, -2x1018 radiolytic superoxide ions
(02) ions per gram were identified in this glass by ESR [1]. Since high-iron phosphate glasses in general
(composition range -0.2<[Fe]/[P]<0.67) have displayed many properties favorable for vitrification of
phosphate-rich high-level wastes such as are present at the Hanford site [2], the first 15 months of the project
were devoted to fundamental studies of (A) the SRTC lithium-cerium-iron-phosphate and (B) various UMR
iron-phosphate glasses. The results of ESR, M6ssbauer, thermal analysis, and gas-evolution studies carried
out in informal collaboration with the UMR and Toyo University (Japan) are reported in [1]. The ESR
results have revealed the unirradiated glasses to possess unusual long-range magnetic structure, which is
qualitatively different that of the crystallized materials. This finding, in conjunction with the other types of
measurements mentioned, led to the tentative proposal that peroxide ions (022-) may have been incorporated
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Griscom, David L. Chemical Decomposition of High-Level Nuclear Waste Storage/Disposal Glasses Under Irradiation, report, June 1, 1999; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc786569/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.