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Title: Contact zones and hydrothermal systems as analogues to repository conditions

Abstract

Radioactive waste isolation efforts in the US are currently focused on examining basalt, tuff, salt, and crystalline rock as candidate rock types to encompass waste repositories. As analogues to near-field conditions, the distributions of radio- and trace-elements have been examined across contacts between these rocks and dikes and stocks that have intruded them. The intensive study of the Stripa quartz monzonite has also offered the opportunity to observe the distribution of uranium and its daughters in groundwater and its relationship to U associated with fracture-filling and alteration minerals. Investigations of intrusive contact zones to date have included (1) a tertiary stock into Precambrian gneiss, (2) a stock into ash flow tuff, (3) a rhyodacite dike into Columbia River basalt, and (4) a kimberlite dike into salt. With respect to temperature and pressure, these contact zones may be considered "worst-case scenario" analogues. Results indicate that there has been no appreciable migration of radioelements from the more radioactive intrusives into the less radioactive country rocks, either in response to the intrusions or in the fracture-controlled hydrological systems that developed following emplacement. In many cases, the radioelements are locked up in accessory minerals, suggesting that artificial analogues to these would make ideal wastemore » forms. Emphasis should now shift to examination of active hydrothermal systems, studying the distribution of key elements in water, fractures, and alteration minerals under pressure and temperature conditions most similar to those expected in the near-field environment of a repository. 14 refs.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (United States)
OSTI Identifier:
60580
Report Number(s):
LBL-18587; CONF-8410311-1
ON: DE85016555
DOE Contract Number:
AC03-76SF00098
Resource Type:
Conference
Resource Relation:
Conference: Workshop on radionuclide migration, Chicago, IL (United States), 1-3 Oct 1984; Other Information: PBD: Oct 1984
Country of Publication:
United States
Language:
English
Subject:
05 NUCLEAR FUELS; 54 ENVIRONMENTAL SCIENCES; RADIOACTIVE WASTE DISPOSAL; RADIONUCLIDE MIGRATION; BASALT; TUFF; SALT DEPOSITS; GROUND WATER; URANIUM; DAUGHTER PRODUCTS; QUARTZ; THORIUM; Yucca Mountain Project

Citation Formats

Wollenberg, H.A., and Flexser, S. Contact zones and hydrothermal systems as analogues to repository conditions. United States: N. p., 1984. Web.
Wollenberg, H.A., & Flexser, S. Contact zones and hydrothermal systems as analogues to repository conditions. United States.
Wollenberg, H.A., and Flexser, S. 1984. "Contact zones and hydrothermal systems as analogues to repository conditions". United States. doi:. https://www.osti.gov/servlets/purl/60580.
@article{osti_60580,
title = {Contact zones and hydrothermal systems as analogues to repository conditions},
author = {Wollenberg, H.A. and Flexser, S.},
abstractNote = {Radioactive waste isolation efforts in the US are currently focused on examining basalt, tuff, salt, and crystalline rock as candidate rock types to encompass waste repositories. As analogues to near-field conditions, the distributions of radio- and trace-elements have been examined across contacts between these rocks and dikes and stocks that have intruded them. The intensive study of the Stripa quartz monzonite has also offered the opportunity to observe the distribution of uranium and its daughters in groundwater and its relationship to U associated with fracture-filling and alteration minerals. Investigations of intrusive contact zones to date have included (1) a tertiary stock into Precambrian gneiss, (2) a stock into ash flow tuff, (3) a rhyodacite dike into Columbia River basalt, and (4) a kimberlite dike into salt. With respect to temperature and pressure, these contact zones may be considered "worst-case scenario" analogues. Results indicate that there has been no appreciable migration of radioelements from the more radioactive intrusives into the less radioactive country rocks, either in response to the intrusions or in the fracture-controlled hydrological systems that developed following emplacement. In many cases, the radioelements are locked up in accessory minerals, suggesting that artificial analogues to these would make ideal waste forms. Emphasis should now shift to examination of active hydrothermal systems, studying the distribution of key elements in water, fractures, and alteration minerals under pressure and temperature conditions most similar to those expected in the near-field environment of a repository. 14 refs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1984,
month =
}

Conference:
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  • Hydrothermal systems in tuffaceous and older sedimentary rocks contain evidence of the interaction of radionuclides in fluids with rock matrix minerals and with materials lining fractures, in settings somewhat analogous to the candidate repository site at Yucca Mountain, NV. Earlier studies encompassed the occurrences of U and Th in a ``fossil`` hydrothermal system in tuffaceous rock of the San Juan Mountains volcanic field, CO. More recent and ongoing studies examine active hydrothermal systems in calderas at Long Valley, CA and Valles, NM. At the Nevada Test Site, occurrences of U and Th in fractured and unfractured rhyolitic tuff that wasmore » heated to simulate the introduction of radioactive waste are also under investigation. Observations to date suggest that U is mobile in hydrothermal systems, but that localized reducing environments provided by Fe-rich minerals and/or carbonaceous material concentrate U and thus attenuate its migration. 11 refs., 6 figs., 1 tab.« less
  • Concrete could comprise a major share of construction materials present in the potential Yucca Mountain high-level radioactive waste repository. Concrete and shotcrete would be used as mechanical support (precast concrete liners), or road bed (invert) in repository emplacement drifts. These drifts could reach at least 150 to 200{degrees}C for extended periods of time, possibly in the presence of fluids. This study characterizes chemical and structural transformations in concrete that may occur as a result of a repository hydrothermal cycle. The specific concrete formulation to be used in the potential Yucca Mountain repository had not been determined at the time ofmore » the experiment. Invert and Fibercrete{sup TM} materials from the Exploratory Studies Facility (ESF) were chosen for these experiments as representatives of standard construction concrete used in this setting.« less
  • Contact zones between intrusive rocks and tuff, basalt, salt and granitic rock were investigated as possible analogues of nuclear waste repository conditions. Results of detailed studies of contacts between quartz monzonite of Laramide age, intrusive into Precambrian gneiss, and a Tertiary monzonite-tuff contact zone indicate that uranium, thorium and other trace elements have not migrated significantly from the more radioactive instrusives into the country rock. Similar observations resulted from preliminary investigations of a rhyodacite dike cutting basalt of the Columbia River plateau and a kimberlitic dike cutting bedded salt of the Salina basin. This lack of radionuclide migration occurred inmore » hydrologic and thermal conditions comparable to, or more severe than those expected in nuclear waste repository environments and over time periods of the order of concern for waste repositories. Attention is now directed to investigation of active hydrothermal systems in candidate repository rock types, and in this regard a preliminary set of samples has been obtained from a core hole intersecting basalt underlying the Newberry caldera, Oregon, where temperatures presently range from 100 to 265{sup 0}C. Results of mineralogical and geochemical investigations of this core should indicate the alteration mineralogy and behavior of radioelements in conditions analogous to those in the near field of a repository in basalt.« less
  • Three conceptual models are presented to illustrate the range of natural hydrothermal convection systems in which vapor-dominated conditions are found. Numerical simulation is used to test the feasibility of these models and to demonstrate geologically plausible evolutionary pathways for each model. 2 figs., 13 refs.
  • Hydrothermal systems in tuffaceous and older sedimentary rocks contain evidence of the interaction of radionuclides in fluids with rock matrix minerals and with materials lining fractures, in settings somewhat analogous to the candidate repository site at Yucca Mountain, NV. Earlier studies encompassed the occurrences of U and Th in a {open_quotes}fossil{close_quotes} hydrothermal system in tuffaceous rock of the San Juan Mountains Volcanic Field, CO. More recent and ongoing studies examine active hydrothermal systems in calderas at Long Valley, CA and Valles, NM. At the Nevada Test Site, occurrences of U and Th in fractured and unfractured rhyolitic tuff that wasmore » heated to simulate the introduction of radioactive waste are also under investigation. Observations to date suggest that U is mobile in hydrothermal systems, but that localized reducing environments provided by Fe-rich minerals and/or carbonaceous materials concentrate U and thus attenuate its migration.« less