Software verification, model validation and hydrogeologic modelling aspects in nuclear waste disposal system simulations : a paradigm shift

Several countries are actively investigating the feasibility of using crystalline rock bodies for the ultimate disposal of radioactive nuclear waste. As part of the concept assessment phase in the Canadian nuclear fuel waste management program, a multidisciplinary research investigation is being conducted across the Lac du Bonnet batholith in southeastern Manitoba; no radioactive materials, other than sealed sources or tracers, are to be emplaced within this rock body. The results of a high‐resolution seismic reflection survey, together with information from a number of deep boreholes, demonstrates that major subhorizontal fractures occur at depths of up to 800 m within the batholith. An integrated interpretation of the seismic data with selected borehole logs shows that warm water is flowing up the major fractures from depth. A natural corollary of these results is that a three‐dimensional seismic reflection survey combined with an appropriate exploratory drilling program has the potential for delineating blocks of a rock body that may be relatively unfractured.

The Canadian Nuclear Fuel Waste Management program is evaluating two basic supported-shell container concepts for used-fuel immobilization.One concept uses a compacted particulate material within the container to sunport a thin, corroston-resistant shell. The other concept, called “the metal-matrix concept”, uses a cast-in-place metal matrix for shell support.This paper describes corrosion studies on the candidate matrix materials, lead, zinc and aluminum-7 wt.7 Si (A1-7 wt.7 Si), in the temperature range 293 to 423 K and the dissolved oxygen content range 8 to 410 mg/L. Test specimens were analyzed for general and localized corrosion and the corrosion products were identified.The results showed that, unlike lead, zinc and Al-7 wt.% Si are susceptible to localized corrosion. Lead showed only low general corrosion rates of 2 to 83 pm/a compared with zinc (36 to 15800 μm/a) and Al-7 wt.% Si (6 to 209 μm/a) in the above temperature and oxygen content ranges. Maximum pit depths of about 0.9 mm on Al-7 wt.% Si and 0.6 mm on zinc were observed. These results indicate that, of the candidate matrix metals studied, lead has the greatest potential to retard radionuclide release from used-fuel disposal containers.

96/05591 Quality analysis/quality control tests for field stabilization/solidification — 2. Untreated waste, sodium silicate solution and solidified waste

Casting Development for Nuclear Fuel Disposal Containers

The sorption of four radionuclides, /sup 90/Sr, /sup 137/Cs, /sup 144/Ce, and /sup 237/Pu, on drill core material from two rock formations in the Canadian Shield has been studied as part of the Canadian Nuclear Fuel Waste Management Program. For all four radionuclides, sorption increased with increased mafic mineral content of the rock. Autoradiographic investigations showed enhanced sorption on dark, or mafic, minerals and high sorption on chlorite infilling material in a closed fracture. Desorption was less complete than sorption after the same equilibration time, indicating a degree of irreversible sorption, or slower desorption kinetics. The effect of surface roughness (measured by mercury porosimetry) on sorption was not as great as that of the chemical and mineral composition of the rock.

The selection of a sorption data base for the geosphere model in the Canadian Nuclear Fuel Waste Management Program

AECL Whiteshell Laboratories (WL), near Winnipeg, Canada has been in operation since the early 1960s. R&D programs carried out at WL include a 60 MW organic-cooled research reactor, which operated from 1965 to 1985, reactor safety research, small reactor development, materials science, post irradiation examinations, chemistry, biophysics and radiation applications. The Canadian Nuclear Fuel Waste Management Program was conducted and continues to operate at WL and also at the nearby Underground Research Laboratory.In the late-1990s, AECL began to consolidate research and development activities at its Chalk River Laboratories (CRL) and began preparations for decommissioning WL. Preparations for decommissioning included a staged shutdown of operations, planning documentation and licensing for decommissioning. As a prerequisite to AECL's application for a decommissioning licence, an environmental assessment (EA) was carried out according to Canadian environmental assessment legislation. The EA concluded in 2002 April when the Federal Environment Minister published his decision that WL decommissioning was not likely to cause significant adverse environmental effects and that no further assessment by a review panel or mediation would be requiredIn 2002 December, the Canadian Nuclear Safety Commission issued a decommissioning licence for WL, valid until December 31, 2008. The licence authorized the first planned phase of site decommissioning as well as the continuation of selected research programs. The six-year licence for Whiteshell Laboratories was the first overall decommissioning license issued for a Canadian Nuclear Research and Test Establishment and was the longest licence term ever granted for a nuclear installation of this complexity in Canada.The first phase of decommissioning is now underway and focuses on decontamination and modifications to nuclear facilities, such as the shielded facilities, the main R&D laboratories and the associated service systems, to achieve a safe state of storage-with-surveillance. Later phases have planned waste management improvements for selected wastes already in storage, eventually followed by final decommissioning of facilities and infrastructure and removal of most wastes from the site.This paper provides an overview of the planning, environmental assessment, licensing, and organizational processes for decommissioning and selected descriptions of decommissioning activities currently underway at AECL Whiteshell Laboratories.

87Sr/ 86Sr values in groundwaters of the East Bull Lake pluton, Superior Province, Ontario, Canada

Technetium-99, produced by the fission of 235U and 239Pu, has a radiological half-life of 2·15 x 105 years and has been dispersed in the environment via weapons testing and releases from establishments using it for medical or industrial purposes. Technetium could also reach the environment via releases from nuclear power plants, nuclear fuel processing facilities or nuclear fuel waste disposal vaults. Environmental impact assessments associated with the licensing of such nuclear facilities usually include analysis of radiation exposure pathways that involve the transport of radionuclides through agricultural soils and their uptake by crop plants. The environmental assessment of the Canadian concept for the permanent disposal of nuclear fuel waste in plutonic rock differs from the assessments required for surface nuclear facilities in that the source of radionuclides in the fuel waste disposal vault is located 500–1000 m deep in a rock mass. Thus, the models for the assessment of this concept must predict radionuclide migration up from the vault, through the geosphere and into the biosphere, and the eventual radiological dose to man [1]. Only radionuclides with very long half-lives could reach the biosphere and, of those, only the most mobile nuclides could escape from the vault and the surrounding rock. Technetium has both of these properties and so is important in the research supporting the Canadian Nuclear Fuel Waste Management Program.

Actinide and rare earth element characteristics of deep fracture zones in the Lac du Bonnet granitic batholith, Manitoba, Canada

For the realization of a deep geological repository, geoscientists have investigated various geological formations and assessed their suitability as host rocks for the long-term disposal of high-level nuclear waste. A fundamental epistemological uncertainty has characterized this geoscientific exploration of the subterranean, evolving not only as a scientific-technical challenge in deep geological disposal projects but also as a sociopolitical one. This paper scrutinizes how the Swiss nuclear waste organization, during its recent drilling campaign, has publicly staged the Opalinus clay as a stable rock in order to make its disposal project feasible and sound. Based on ethnographic fieldwork as well as document and media analysis, it traces how science communication experts have created and arranged a series of maps, models, and materials to make the subterranean tangible to a surface audience over the course of the campaign. Strategically assembled at specific events, it shows that these political materials did not simply represent subterranean spaces but constituted a stratified subterranean geology on the surface. On this basis, this paper underlines the performative dimension of geology and the key importance of stabilizing geology in science-society encounters for deep geological disposal projects to advance. By illustrating how the subterranean has come to matter and became politically significant in Switzerland's contentious nuclear (waste) history, this paper contributes to a better understanding of the constitutive role of geology for imagining a postnuclear future.

Effects of contact time, pH, and temperature on Eu(III) sorption onto MX-80 bentonite

The policy of the United States is to dispose of high-level nuclear waste underground in geologic repositories. The U.S. Department of Energy (DOE) has been developing plans for a repository to be located at Yucca Mountain, Nevada, and submitted a license application to the U.S. Nuclear Regulatory Commission (NRC) for that repository in June 2008. This paper discusses DOE’s bases for and approach to modeling the localized and general corrosion aspects of the Alloy 22 (UNS N06022) outer shell of the container that DOE plans to use for encapsulating the waste in the repository. The modeling is necessary to predict the corrosion behavior for the container’s extraordinarily long “service period”—more than a million years.

The primary goal of the US Subseabed Disposal Program (SDP) is to assess the technical and environmental feasibility of disposing of high-level nuclear waste in deep-sea sediments. The subseabed biology program is charged with assessing possible ecosystem effects of radionuclides as well as possible health effects to man from radionuclides which may be released in the deep sea and transported to the ocean surface. Current biological investigations are attempting to determine benthic community structure; benthic community metabolism; the biology of deep-sea mobile scavengers; the faunal composition of midwater nekton; rates of microbial processes; and the radiation sensitivity of deep-sea organisms. Existing models of the dispersal of radionuclides in the deep sea have not considered many of the possible biological mechanisms which may influence the movement of radionuclides. Therefore, a multi-compartment foodweb model is being developed which considers both biological and physical influences on radionuclide transport. This model will allow parametric studies to be made of the impact on the ocean environment and on man of potential releases of radionuclides.

Area-wide geologic studies have been conducted in six states to identify sites for detailed site characterization studies, and ultimately the construction of the nation9s first high level nuclear waste disposal facility. Host rock types in the respective states under consideration include basalts in Washington state, tuffs in Nevada, bedded evaporites (salts) in Utah and Texas, and diapiric salt in Mississippi and Louisiana. An exploratory shaft facility (ESF) is an integral part of the detailed site characterization activities mandated by the Nuclear Waste Policy Act of 1982 (U.S. Congress, 1983). One of the primary objectives of the exploratory shaft is to provide access to the target repository horizon so that detailed in situ testing can be performed to evaluate site suitability for repository construction, materials characterization, model validation, etc. In addition, the ESF will provide a means of evaluating construction conditions and applicable methods for the potential repository, and for characterizing the geologic and hydrologic conditions of the materials overlying the target horizon. Seven salt sites in four states have been considered for ESF preliminary designs (Parsons Brinckerhoff/PB-KBB, 1983). While salt has several advantages for waste isolation, such as its impermeability, thermal and visco-plastic properties, etc., it also presents some unusual design and construction problems. The solubility and visco-plastic nature of salt requires special lining designs and construction to isolate and control water inflow and to avoid excessive stress build-up due to the long term deformations (creep) of salt. Other major geotechnical factors involved in the design of the ESF, and of special interest to Texas are the protection of fresh water aquifers (particularly the Ogallala and Dockum formations in the Texas Panhandle), ground stabilization and ground-water control during shaft sinking (anticipated to require ground freezing methods through the upper 1,000 ft of overburden at the Texas sites), seismic stresses, in situ stresses, ground-water conditions in non-fresh water aquifers, etc. Exploratory borings will be drilled for each shaft at a salt site during ESF Final Design activities. The boring program will include comprehensive borehole and laboratory testing for the purpose of verifying or modifying design assumptions, as required.