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Title: Modeling acid-gas generation from boiling chloride brines

This study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate. Simple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150 C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimentalmore » data from other studies. The combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation experiments do not represent expected conditions in an emplacement drift, but nevertheless illustrate the potential for acid-gas generation at moderate temperatures (<150 C).« less
Authors:
; ; ;
Publication Date:
OSTI Identifier:
979022
Report Number(s):
LBNL-2849E
Journal ID: ISSN 1467-4866; TRN: US1003072
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochemical Transactions; Journal Volume: 10; Related Information: Journal Publication Date: 2009
Research Org:
Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
Sponsoring Org:
Earth Sciences Division
Country of Publication:
United States
Language:
English
Subject:
54; 58; ATMOSPHERIC PRESSURE; BOILING; BRINES; CALCIUM CHLORIDES; CHEMISTRY; CHLORIDES; CONDENSATES; DISSOCIATION; DISTILLATION; EVALUATION; EVAPORATION; EVAPORATION MODEL; GASES; NUCLEAR FUELS; POSITIONING; RADIOACTIVE WASTES; TRANSPORT; YUCCA MOUNTAIN