PERFORMANCE OF A BURIED RADIOACTIVE HIGH LEVEL WASTE GLASS AFTER 24 YEARS Page: 4 of 39
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The return to the forward dissolution rate is undesirable for long term performance of
glass in a disposal environment. The return to the forward rate of dissolution raises
additional questions about (1) how short term accelerated laboratory performance tests
relate to long term performance in a disposal environment and (2) whether the forward rate
of dissolution or the steady state rate of dissolution should be used for repository risk
The study of HLW glasses that have been buried for long periods of time in a disposal
environment and/or natural analog studies are the only ways to elucidate whether short term
accelerated laboratory durability test performance and glass durability models are related to
the long term durability and performance of a waste glass in a disposal environment. The
nature of the leached layer formed, the overall glass dissolution, and the migration of both
radioactive and non-radioactive species into the surrounding soil must all be assessed.
1.1 Field Tests of Simulated and Alpha-Doped HLW Glasses
Many field tests of simulated (non-radioactive) HLW glass durability have been
performed and reviews of the subject are available elsewhere [4,5,6]. In the non-
radioactive field tests in natural groundwaters, the glasses proved to be as durable and/or
more durable than indicated during accelerated laboratory testing [4,5].
Tests have been performed on non-radioactive simulated glasses and/or glasses doped
with alpha emitting radionuclides such as 134Cs, 90Sr, and 239Pu. These glasses were
subjected to a 5 year burial in the Boom clay at Mol, Belgium at temperatures of 160C,
900C, and 1700C for periods of 2 to 7.5 years. Subsequent experiments were performed
with four glasses doped with alpha emitting 238-242PuG2, mNpO2, and/or 241Am203
[7,8,9,10]. These glasses were simultaneously subjected to gamma fields during burial at
900C for 5 years. In the case of the alpha emitting radionuclides in the gamma irradiation
fields, the durability of the glass was similar to that of accelerated laboratory testing .
The leached layers of the glasses buried in Boom clay were examined by scanning
electron microscopy coupled with electron diffraction. The SON68 (R7T7) French glass
had a leached layer of -200 pm that was enriched at the top in Al and Si and reduced in Ca
and Na. Enrichment in K and Mg was attributed to sorption from the Boom clay. On top of
the leached layer were precipitates enriched in Al, Si, Mg, Fe, and K. In-between the
leached layer and the precipitates was a region depleted in Si, Al, and Ca. The Belgian
glass SM513 (PAMELA) had a 350 pm leached layer enriched in Ti and Al and reduced in
Na, Ca, and Mg. Again K was enriched in the layer and attributed to be from the burial
medium, the Boom clay. Glass SM527 (PAMELA) had no reaction layer but a thin
precipitate layer enriched in K, Mg, Si, and Al. Lastly, Glass WG124 (a silicate glass) had
a 500-600 pm layer with a double structure. The outer layer was enriched in Fe, Al, Mg
and depleted in Si, Ca, Na, and K while the inner layer was depleted in Mg, Si, Ca, and Na.
Precipitates enriched in Si, Al, Mg, Fe, K and S were found on the outermost surface .
The Boom clay burial glass with the least reaction layer was the SM527 glass which
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Jantzen, C; Daniel Kaplan, D; Ned Bibler, N; David Peeler, D & John Plodinec, J. PERFORMANCE OF A BURIED RADIOACTIVE HIGH LEVEL WASTE GLASS AFTER 24 YEARS, article, May 5, 2008; [Aiken, South Carolina]. (digital.library.unt.edu/ark:/67531/metadc898741/m1/4/: accessed June 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.