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Title: Vitrified hillforts as anthropogenic analogues for nuclear waste glasses - project planning and initiation

Abstract

Nuclear waste must be deposited in such a manner that it does not cause significant impact on the environment or human health. In some cases, the integrity of the repositories will need to sustain for tens to hundreds of thousands of years. In order to ensure such containment, nuclear waste is frequently converted into a very durable glass. It is fundamentally difficult, however, to assure the validity of such containment based on short-term tests alone. To date, some anthropogenic and natural volcanic glasses have been investigated for this purpose. However, glasses produced by ancient cultures for the purpose of joining rocks in stonewalls have not yet been utilized in spite of the fact that they might offer significant insight into the long-term durability of glasses in natural environments. Therefore, a project is being initiated with the scope of obtaining samples and characterizing their environment, as well as to investigate them using a suite of advanced materials characterization techniques. It will be analysed how the hillfort glasses may have been prepared, and to what extent they have altered under in-situ conditions. The ultimate goals are to obtain a better understanding of the alteration behaviour of nuclear waste glasses and its compositionalmore » dependence, and thus to improve and validate models for nuclear waste glass corrosion. The paper deals with project planning and initiation, and also presents some early findings on fusion of amphibolite and on the process for joining the granite stones in the hillfort walls.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1340857
Report Number(s):
PNNL-SA-118241
Journal ID: ISSN 1743-7601; 49141; EY804910A
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: International Journal of Sustainable Development and Planning, 11(6):897-906; Journal Volume: 11; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
Nuclear; waste; long-lived; glass; anthropogenic; analogue; ageing; leaching; hillfort; hill-fort; rampart; amphibolite; Broborg; Environmental Molecular Sciences Laboratory

Citation Formats

Sjoblom, Rolf, Weaver, Jamie L., Peeler, David K., Mccloy, John S., Kruger, Albert A., Ogenhall, E., and Hjarthner-Jolder, E.. Vitrified hillforts as anthropogenic analogues for nuclear waste glasses - project planning and initiation. United States: N. p., 2016. Web. doi:10.2495/SDP-V11-N6-897-906.
Sjoblom, Rolf, Weaver, Jamie L., Peeler, David K., Mccloy, John S., Kruger, Albert A., Ogenhall, E., & Hjarthner-Jolder, E.. Vitrified hillforts as anthropogenic analogues for nuclear waste glasses - project planning and initiation. United States. doi:10.2495/SDP-V11-N6-897-906.
Sjoblom, Rolf, Weaver, Jamie L., Peeler, David K., Mccloy, John S., Kruger, Albert A., Ogenhall, E., and Hjarthner-Jolder, E.. 2016. "Vitrified hillforts as anthropogenic analogues for nuclear waste glasses - project planning and initiation". United States. doi:10.2495/SDP-V11-N6-897-906.
@article{osti_1340857,
title = {Vitrified hillforts as anthropogenic analogues for nuclear waste glasses - project planning and initiation},
author = {Sjoblom, Rolf and Weaver, Jamie L. and Peeler, David K. and Mccloy, John S. and Kruger, Albert A. and Ogenhall, E. and Hjarthner-Jolder, E.},
abstractNote = {Nuclear waste must be deposited in such a manner that it does not cause significant impact on the environment or human health. In some cases, the integrity of the repositories will need to sustain for tens to hundreds of thousands of years. In order to ensure such containment, nuclear waste is frequently converted into a very durable glass. It is fundamentally difficult, however, to assure the validity of such containment based on short-term tests alone. To date, some anthropogenic and natural volcanic glasses have been investigated for this purpose. However, glasses produced by ancient cultures for the purpose of joining rocks in stonewalls have not yet been utilized in spite of the fact that they might offer significant insight into the long-term durability of glasses in natural environments. Therefore, a project is being initiated with the scope of obtaining samples and characterizing their environment, as well as to investigate them using a suite of advanced materials characterization techniques. It will be analysed how the hillfort glasses may have been prepared, and to what extent they have altered under in-situ conditions. The ultimate goals are to obtain a better understanding of the alteration behaviour of nuclear waste glasses and its compositional dependence, and thus to improve and validate models for nuclear waste glass corrosion. The paper deals with project planning and initiation, and also presents some early findings on fusion of amphibolite and on the process for joining the granite stones in the hillfort walls.},
doi = {10.2495/SDP-V11-N6-897-906},
journal = {International Journal of Sustainable Development and Planning, 11(6):897-906},
number = 6,
volume = 11,
place = {United States},
year = 2016,
month = 9
}
  • How does glass alter with time? For the last hundred years this has been an important question to the fields of object conservation and archeology to ensure the preservation of glass artifacts. This same question is part of the development and assessment of durable glass waste forms for the immobilization of nuclear wastes. Researchers have developed experiments ranging from simple to highly sophisticated to answer this question, and, as a result, have gained significant insight into the mechanisms that drive glass alteration. However, the gathered data have been predominately applicable to only short-term alteration times, i.e. over the course ofmore » decades. What has remained elusive is the long-term mechanisms of glass alteration[1]. These mechanisms are of particular interest to the international nuclear waste glass community as they strive to ensure that vitrified products will be durable for thousands to tens of thousands of years. For the last thirty years this community has been working to fill this research gap by partnering with archeologists, museum curators, and geologists to identify hundred to million-year old glass analogues that have altered in environments representative of those expected at potential nuclear waste disposal sites. The process of identifying a waste glass relevant analogue is challenging as it requires scientists to relate data collected from short-term laboratory experiments to observations made from long-term analogues and extensive geochemical modeling.« less
  • Most tests of the dissolution behavior of glasses quote the leach rate, often measured in flowing solutions. In the past, it has been pointed out that this may not be the rate-determining factor for the dissolution of glass in a radioactive waste repository because of the very small flow rate of water past the glass surface. Under these conditions, the rate of removal of elements from the glass would be controlled by the flow rate and the effective saturation solubility of the glass in the water, or, in stagnant conditions, by the rate of diffusion of species dissolved in themore » water away from the glass surface. Simple quantitative models are developed to provide a framework for the discussion of these effects, and they indicate that in cases of practical importance it is indeed solubility and either water access or diffusion that together limit the rate of dissolution of the glass. It can be concluded that effective leach rates in a repository will be below 10/sup -7/ g X cm/sup -2/ X day/sup -1/, a figure that in other studies has given a clear margin of long-term safety for radiological purposes.« less
  • No abstract prepared.
  • The common observation of glasses persisting in natural environments for long periods of time (up to tens of millions of years) provides compelling evidence that these materials can be kinetically stable in a variety of subsurface environments. This paper reviews how natural and historical synthesized glasses can be employed as natural analogues for understanding and projecting the long-term alteration of high-level nuclear waste glasses. The corrosion of basaltic glass results in many of the same alteration features found in laboratory testing of the corrosion of high-level radioactive waste glasses. Evidence has also been found indicating similarities in the rate controllingmore » processes, such as the effects of silica concentration on corrosion in groundwater and in laboratory leachates. Naturally altered rhyolitic glasses and tektites provide additional evidence that can be used to constrain estimates of long-term waste glass alteration. When reacted under conditions where water is plentiful, the corrosion for these glasses is dominated by network hydrolysis, while the corrosion is dominated by molecular water diffusion and secondary mineral formation under conditions where water contact is intermittent or where water is relatively scarce. Synthesized glasses that have been naturally altered result in alkali-depleted alteration features that are similar to those found for natural glasses and for nuclear waste glasses. The characteristics of these alteration features appear to be dependent on the alteration conditions which affect the dominant reaction processes during weathering. In all cases, care must be taken to ensure that the information being provided by natural analogues is related to nuclear waste glass corrosion in a clear and meaningful way.« less
  • This investigation outlines the use of natural analogues as a means of assessing the long-term performance of actinide host phases in crystalline nuclear waste forms. We employed several analytical techniques to study the mineral zirconolite, an important actinide host phase in Synroc and tailored ceramics. The following conclusions were reached: (1) Natural zirconolite experiences a crystalline to aperiodic transformation at doses of approximately 10{sup 15} to 10{sup 16} {alpha}/ma (0.08-1.0 dpa), consistent with the results of accelerated damage testing on synthetic zirconolite. (2) Damage microstructures are consistent with the accumulation and overlap of alpha-recoil collision cascades, resulting in aperiodic domainsmore » which increase in volume as a function of dose. (3) There is evidence for long-term annealing of alpha-recoil damage in zirconolite at a rate 2-5 times slower than in the structurally related mineral pyrochlore. (4) Analysis of data from the only documented natural zirconolites to show hydrothermal alteration [resulting from F- and P-rich aqueous fluids at T = 500-600{degrees}C and P = 2 kb, Giere and Williams (14)], suggests that Th and U were released to the fluid phase. (5) The effects of low temperature alteration of radiation damaged zirconolite by a Si-rich ground water or fluid phase were identified in the oldest (2.5 x 10{sup 9} yr) sample in our research collection. Alteration involved incorporation of Si along microfractures at the expense of Ca, Ti, and Fe, but Tb and U remained immobile. In this same sample, there is evidence for migration of at least 50% of the radiogenic Pb from both unaltered and altered areas of zirconolite. Most of the Pb may have been retained within the sample as fine precipitates of galena (PbS).« less