High-level Nuclear Waste Repository Site Research Articles

Multi-scale groundwater flow modeling during temperate climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

Forsmark in Sweden has been proposed as the site of a geological repository for spent high-level nuclear fuel, to be located at a depth of approximately 470 m in fractured crystalline rock. The safety assessment for the repository has required a multi-disciplinary approach to evaluate the impact of hydrogeological and hydrogeochemical conditions close to the repository and in a wider regional context. Assessing the consequences of potential radionuclide releases requires quantitative site-specific information concerning the details of groundwater flow on the scale of individual waste canister locations (1–10 m) as well as details of groundwater flow and composition on the scale of groundwater pathways between the facility and the surface (500 m to 5 km). The purpose of this article is to provide an illustration of multi-scale modeling techniques and the results obtained when combining aspects of local-scale flows in fractures around a potential contaminant source with regional-scale groundwater flow and transport subject to natural evolution of the system. The approach set out is novel, as it incorporates both different scales of model and different levels of detail, combining discrete fracture network and equivalent continuous porous medium representations of fractured bedrock.

Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

The impact of periglacial and glacial climate conditions on groundwater flow in fractured crystalline rock is studied by means of groundwater flow modeling of the Forsmark site, which was recently proposed as a repository site for the disposal of spent high-level nuclear fuel in Sweden. The employed model uses a thermal-hydraulically coupled approach for permafrost modeling and discusses changes in groundwater flow implied by the climate conditions found over northern Europe at different times during the last glacial cycle (Weichselian glaciation). It is concluded that discharge of particles released at repository depth occurs very close to the ice-sheet margin in the absence of permafrost. If permafrost is included, the greater part discharges into taliks in the periglacial area. During a glacial cycle, hydraulic gradients at repository depth reach their maximum values when the ice-sheet margin passes over the site; at this time, also, the interface between fresh and saline waters is distorted the most. The combined effect of advances and retreats during several glaciations has not been studied in the present work; however, the results indicate that hydrochemical conditions at depth in the groundwater flow model are almost restored after a single event of ice-sheet advance and retreat.

Effects on groundwater flow of abandoned engineered structures for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

Effects on groundwater flow of abandoned engineered structures in relation to a potential geological repository for spent high-level nuclear fuel in fractured crystalline rock at the Forsmark site, Sweden, are studied by means of numerical modeling. The effects are analyzed by means of particle tracking, and transport-related performance measures are calculated. The impacts of abandoned, partially open repository tunnels are studied for two situations with different climate conditions: a “temperate” climate case with present-day boundary conditions, and a generic future “glacial” climate case with an ice sheet covering the repository. Then, the impact of abandoned open boreholes drilled through the repository is studied for present-day climate conditions. It is found that open repository tunnels and open boreholes can act as easy pathways from repository level to the ground surface; hence, they can attract a considerable proportion of particles released in the model at deposition hole positions within the repository. The changed flow field and flow paths cause some changes in the studied performance measures, i.e., increased flux at the deposition holes and decreased transport lengths and flow-related transport resistances. However, these effects are small and the transport resistance values are still high.

Overview of hydrogeological safety assessment modeling conducted for the proposed high-level nuclear waste repository site at Forsmark, Sweden

Overview of hydrogeological safety assessment modeling conducted for the proposed high-level nuclear waste repository site at Forsmark, Sweden

Overview of hydrogeological site-descriptive modeling conducted for the proposed high-level nuclear waste repository site at Forsmark, Sweden

In an essay in a previous issue of Hydrogeology Journal, Selroos and Follin (2014) outlined the hydrogeological sitedescriptive modeling performed regarding the Forsmark site in Sweden in order to support an application for a future repository for high-level spent nuclear fuel. The essay was accompanied by three individual reports (Follin and Stigsson 2014; Follin et al. 2014; Follin and Hartley 2014) where more detail was given on various modeling aspects (e.g. parameterization of a deformation zone model, development of a discrete fracture network model, and model integration and confirmatory testing of the integrated model against various types of data). The aim of the site-descriptive hydrogeological modeling was to develop a hydrogeological account of the past and present conditions at the site by analyzing, assessing, and modeling the data obtained during the stage of surfacebased site characterization. Corresponding site-descriptive models for other earth science disciplines were also developed; the combination of these models constitutes an integrated site-descriptive model of the site and its regional setting, including the current state of the geosphere and the biosphere as well as natural processes affecting long-term evolution. The process and experiences of developing an inter-disciplinary site-descriptive model for the Forsmark site is discussed in detail in Andersson et al. (2013). In the current issue of Hydrogeology Journal, corresponding modeling performed as part of the safety assessment supporting the application is summarized. Whereas the site-descriptive modeling dealt with past and present conditions, the safety assessment deals with the long-term safety and, hence, future conditions. The objectives of the hydrogeological modelling performed as part of the safety assessment are outlined here. In addition, the individual modeling efforts are brought into a safety assessment context in order to exemplify and illustrate how the modelling supports the assessment end-point, i.e. to show regulatory compliance. The Swedish Nuclear Fuel and Waste Management Company (SKB) is responsible for the handling and final disposal of all nuclearwaste in Sweden. The concept developed for geological disposal is denoted ‘KBS-3’ and consists of copper canisters deposited in vertical deposition holes under the floor of deposition tunnels located at approximately 500 m depth in crystalline bedrock (SKB 1983; Banwart et al. 1997; Hedin et al. 2001; Thegerstrom and Olsson 2011). The canisters have a cast-iron insert to provide mechanical stability, and are surrounded by bentonite clay in the deposition hole. The tunnels are backfilled and pumping that has been draining the tunnels is stopped; thereafter, groundwater begins to resaturate the repository. The KBS-3 system is thus a multibarrier system where the three independent barriers are the copper canister, the bentonite buffer, and the bedrock. The safety assessment of which the present modeling is a part, is denoted ‘SR-Site’ (SKB 2011; Hedin et al. 2011) and was a major part of the application to obtain a permit to construct a repository for spent high-level nuclear fuel at Forsmark. The application was submitted to the relevant Swedish authorities inMarch 2011; if the present application is approved within the forecasted time horizon, repository construction could start in 2019. Further detailed characterization and monitoring will be performed in parallel with construction and will provide a basis for future safety assessments. After subsequent applications, based on the renewed safety assessments and approval of a licence, the repository could be in operation around 2030 and then be one of the first such operational repositories in the world. This essay serves as an introduction to three reports in this issue of Hydrogeology Journal (Joyce et al. 2014; Received: 29 August 2013 /Accepted: 18 June 2014 Published online: 12 July 2014

A transmissivity model for deformation zones in fractured crystalline rock and its possible correlation to in situ stress at the proposed high-level nuclear waste repository site at Forsmark, Sweden

The Forsmark site was recently proposed by the Svensk Karnbranslehantering AB (SKB) to serve as the potential site for construction of a future geological repository for spent high-level nuclear fuel at about 470 m depth in fractured crystalline rock. The considerations included, among other things, distance from regionally significant deformation zones with highly strained rock, lithological homogeneity, low hydraulic conductivity, groundwater salinity with an acceptable range, and lack of potential mineral resources. This report describes the calculation of transmissivity of deduced deformation zones at Forsmark and the transmissivity model used in the regional groundwater flow modeling carried out in support of the integrated site description. Besides significant decrease with increasing depth (more than four orders of magnitude over a depth of about 1 km), the calculated transmissivity values also reveal considerable spatial variability along the strikes of the zones, i.e. lateral heterogeneity (more than two orders of magnitude). A hydro-mechanical coupling is discussed, based on presented models for the tectonic evolution and the principal stress tensor. Tentatively, laboratory-scale relationships developed from normal stress experiments on a single fracture in crystalline rock can be used to estimate the maximum values of transmissivity of deduced deformation zones at Forsmark.

A methodology to constrain the parameters of a hydrogeological discrete fracture network model for sparsely fractured crystalline rock, exemplified by data from the proposed high-level nuclear waste repository site at Forsmark, Sweden

The large-scale geological structure of the crystalline rock at the proposed high-level nuclear waste repository site at Forsmark, Sweden, has been classified in terms of deformation zones of elevated fracture frequency. The rock between deformation zones was divided into fracture domains according to fracture frequency. A methodology to constrain the geometric and hydraulic parameters that define a discrete fracture network (DFN) model for each fracture domain is presented. The methodology is based on flow logging and down-hole imaging in cored boreholes in combination with DFN realizations, fracture connectivity analysis and pumping test simulations. The simulations suggest that a good match could be obtained for a power law size distribution where the value of the location parameter equals the borehole radius but with different values for the shape parameter, depending on fracture domain and fracture set. Fractures around 10–100 m in size are the ones that typically form the connected network, giving inflows in the simulations. The report also addresses the issue of up-scaling of DFN properties to equivalent continuous porous medium (ECPM) bulk flow properties. Comparisons with double-packer injection tests provide confidence that the derived DFN formulation of detailed flows within individual fractures is also suited to simulating mean bulk flow properties and their spatial variability.

Approaches to confirmatory testing of a groundwater flow model for sparsely fractured crystalline rock, exemplified by data from the proposed high-level nuclear waste repository site at Forsmark, Sweden

The Svensk Karnbranslehantering AB (SKB) has proposed the Forsmark site as a future repository for spent high-level nuclear fuel, involving disposal at about 470 m depth in sparsely fractured crystalline bedrock. An essential part of the completed inter-disciplinary site investigation was to develop an integrated account of the site and its regional setting, including the current state of the geosphere and the biosphere as well as natural processes affecting long-term evolution. First, this report recollects the integrated understanding and some key hydraulic characteristics of the crystalline bedrock at Forsmark along with a description of the flow model set-up and the methodology used for paleoclimatic flow modeling. Second, the protocol used for site-scale groundwater flow and solute transport modeling is demonstrated. In order to conduct a quantitative assessment of groundwater flow paths at Forsmark, the standard guide for groundwater flow modeling was elaborated on, to support both discrete and porous media flow approaches. In total, four independent types of data were used to confirm that the final groundwater flow model for the crystalline bedrock was representative of site conditions.

Sensitivity in volcanic hazard assessment for the Yucc Mountain high-level nuclear waste repository site: the model and the dat : Chih-Hsiang Ho, Mathematical Geology, 27(2), 1995, pp 239–258

Sensitivity in volcanic hazard assessment for the Yucc Mountain high-level nuclear waste repository site: the model and the dat : Chih-Hsiang Ho, Mathematical Geology, 27(2), 1995, pp 239–258

Sensitivity in volcanic hazard assessment for the Yucca Mountain high-level nuclear waste repository site: The model and the data

Both advocates and critics disagree on the significance and interpretation of critical geological features which relate to the safety and suitability of Yucca Mountain as a site for the construction of a high-level radioactive waste repository. Recent volcanism in the vicinity of Yucca Mountain is recognized readily by geologists and others with a knowledge of nuclear regulatory requirements as an important factor in determining future public and environmental safety. We regard basaltic volcanism as direct and unequivocal evidence of deep-seated geologic instability. Direct disruption of a repository site by basaltic volcanism therefore is a possibility. In this paper, sensitivity analysis of volcanic hazard assessment for the Yucca Mountain site is performed, taking into account some significant geological factors raised by experts. Three types of models are considered in the sensitivity data analysis. The first model assumes that both past and future volcanic activities follow a Homogeneous Poisson Process (HPP). The second model uses a Weibull Process (WP) to estimate the instantaneous recurrence rate based on the historical data at NTS (the Nevada Test Site). The model then switches from a WP of past events to a predictive HPP. The third model assumes that the prior historical trend based on a WP would continue for future activities. Hazards (at least one disruptive event during the next 10,000 years) using both classical and Bayesian approaches are evaluated based on the data for the following two observation periods: Pliocene and younger, and Quaternary. Combinations of various counts of events at volcanic centers of controversy and inclusion (or exclusion) of the youngest date at Lathrop Wells Center (=0.01 Ma) generate 90 different data sets. Sensitivity analysis is performed for each data set and the minimum and the maximum hazards for each model are summarized. We conclude that the estimated overall probability of at least one disruption of a repository at the Yucca Mountain site by basaltic volcanism during the next 10,000 years is bounded between 2.02×105 and 6.57×10−3.

Simulation of the Arid Climate of the Southern Great Basin Using a Regional Climate Model

Abstract As part of the development effort of a regional climate model (RCM)for the southern Great Basin, this paper present savalidation analysis of the climatology generated by a high-resolution RCM driven by observations. The RCM is aversion of the National Center for atmospheric Research–Pennsylvania State University mesoscale model, version 4 (MM4), modified for application to regional climate simulation. Two multiyear simulations, for the periods 1 January 1982 to 31 December 1983 and 1 January 1988 to 25 April 1989, were performed over the western United States with the RCM driven by European Centre for Medium-Range Weather Forecasts analyses of observations. The model resolution is 60 km. This validation analysis is the first phase of a project to produce simulations of future climate scenarios over a region surrounding Yucca Mountain, Nevada, the only location currently being considered as a potential high-level nuclear-waste repository site. Model-produced surface air temperatures and precipitat...

Geologic uncertainty in a regulatory environment: an example from the potential Yucca Mountain Nuclear Waste Repository site : Environ Geol Water Sci V18, N3, Nov–Dec 1991, P171–184

Regulatory geologists are concerned with predicting the performance of sites proposed for waste disposal or for remediation of existing pollution problems. Geologic modeling of these sites requires large-scale expansion of knowledge obtained from very limited sampling. This expansion induces considerable uncertainty into the geologic models of rock properties that are required for modeling the predicted performance of the site. One method for assessing this uncertainty is through nonparametric geostatistical simulation. Simulation can produce a series of equiprobable models of a rock property of interest. Each model honors measured values at sampled locations, and each can be constructed to emulate both the univariate histogram and the spatial covariance structure of the measured data. Computing a performance model for a number of geologic simulations allows evaluation of the effects of geologic uncertainty. A site may be judged acceptable if the number of failures to meet a particular performance criterion produced by these computations is sufficiently low. A site that produces too many failures may be either unacceptable or simply inadequately described. The simulation approach to addressing geologic uncertainty is being applied to the potential high-level nuclear waste repository site at Yucca Mountain, Nevada, U.S.A. Preliminary geologic models of unsaturated permeability have been created that reproduce observed statistical properties reasonably well. A spread of unsaturated groundwater travel times has been computed that reflects the variability of those geologic models. Regions within the simulated models exhibiting the greatest variability among multiple runs are candidates for obtaining the greatest reduction in uncertainty through additional site characterization.

Risk assessment for the Yucca Mountain high-level nuclear waste repository site: Estimation of volcanic disruption

In this article, we model the volcanism near the proposed nuclear waste repository at Yucca Mountain, Nevada, U.S.A. by estimating the instantaneous recurrence rate using a nonhomogeneous Poisson process with Weibull intensity and by using a homogeneous Poisson process to predict future eruptions. We then quantify the probability that any single eruption is disruptive in terms of a (prior) probability distribution, since not every eruption would result in disruption of the repository. Bayesian analysis is performed to evaluate the volcanic risk. Based on the Quaternary data, a 90% confidence interval for the instantaneous recurrence rate near the Yucca Mountain site is (1.85×10−6/yr, 1.26×10−5/yr). Also, using-these confidence bounds, the corresponding 90% confidence interval for the risk (probability of at least one disruptive eruption) for an isolation time of 104 years is (1.0×10−3, 6.7×10−3), if it is assumed that the intensity remains constant during the projected time frame.

Precipitation Estimation in Mountainous Terrain Using Multivariate Geostatistics. Part II: Isohyetal Maps

Abstract Values of average annual precipitation (AAP) may be important for hydrologic characterization of a potential high-level nuclear-waste repository site at Yucca Mountain, Nevada. Reliable measurements of AAP are sparse in the vicinity of Yucca Mountain, and estimates of AAP were needed for an isohyetal mapping over a 2600-square-mile watershed containing Yucca Mountain. Estimates were obtained with a multivariate geostatistical model developed using AAP and elevation data from a network of 42 precipitation stations in southern Nevada and southeastern California. An additional 1531 elevations were obtained to improve estimation accuracy. Isohyets representing estimates obtained using univariate geostatistics (kriging) defined a smooth and continuous surface. Isohyets representing estimates obtained using multivariate geostatistics (cokriging) defined an irregular surface that more accurately represented expected local orographic influences on AAP. Cokriging results included a maximum estimate within...

Geologic uncertainty in a regulatory environment: An example from the potential Yucca Mountain nuclear waste repository site

Regulatory geologists are concerned with predicting the performance of sites proposed for waste disposal or for remediation of existing pollution problems. Geologic modeling of these sites requires large-scale expansion of knowledge obtained from very limited sampling. This expansion induces considerable uncertainty into the geologic models of rock properties that are required for modeling the predicted performance of the site. One method for assessing this uncertainty is through nonparametric geostatistical simulation. Simulation can produce a series of equiprobable models of a rock property of interest. Each model honors measured values at sampled locations, and each can be constructed to emulate both the univariate histogram and the spatial covariance structure of the measured data. Computing a performance model for a number of geologic simulations allows evaluation of the effects of geologic uncertainty. A site may be judged acceptable if the number of failures to meet a particular performance criterion produced by these computations is sufficiently low. A site that produces too many failures may be either unacceptable or simply inadequately described. The simulation approach to addressing geologic uncertainty is being applied to the potential high-level nuclear waste repository site at Yucca Mountain, Nevada, U.S.A. Preliminary geologic models of unsaturated permeability have been created that reproduce observed statistical properties reasonably well. A spread of unsaturated groundwater travel times has been computed that reflects the variability of those geologic models. Regions within the simulated models exhibiting the greatest variability among multiple runs are candidates for obtaining the greatest reduction in uncertainty through additional site characterization.

Perceptions, fear, and economic loss: an application of prospect theory to environmental decision making

Most of the analysis of costs associated with the introduction of risky prospects has concerned contingent costs amenable to insurance programs. An important missing element is the current cost associated with changes in uncertainty. These costs are not amenable to insurance plans and require compensation in order to prevent transfers. In a novel approach, this paper develops an application of prospect theory to such questions, in an intergenerational context. The importance of such an application is demonstrated in a case study of the high-level nuclear waste repository (HNWR) siting decision. As a case study, the costliness of obtaining some elements of the analysis leads to a simulation approach, comparing prospect costs at the three sites that were under consideration by the U.S. Department of Energy. Finding that such costs can be large, we argue for a reassessment of current risk analysis approaches. On a policy note, on the basis of the prospect cost analysis here, the choice of the Yucca Mountain, Nevada, HNWR site seems ill-advised.

Permian salt dissolution, alkaline lake basins, and nuclear-waste storage, Southern High Plains, Texas and New Mexico

Areas of Permian salt dissolution associated with 15 large alkaline lake basins on and adjacent to the Southern High Plains of west Texas and eastern New Mexico suggest formation of the basins by collapse of strata over the dissolution cavities. However, data from 6 other alkaline basins reveal no evidence of underlying salt dissolution. Thus, whether the basins were initiated by subsidence over the salt dissolution areas or whether the salt dissolution was caused by infiltration of overlying lake water is conjectural. However, the fact that the lacustrine fill in Mound Lake greatly exceeds the amount of salt dissolution and subsidence of overlying beds indicates that at least Mound Lake basin was antecedent to the salt dissolution. The association of topography, structure, and dissolution in areas well removed from zones of shallow burial emphasizes the susceptibility of Permian salt-bed dissolution throughout the west Texas–eastern New Mexico area. Such evidence, combined with previous studies documenting salt-bed dissolution in areas surrounding a proposed high-level nuclear-waste repository site in Deaf Smith County, Texas, leads to serious questions about the rationale of using salt beds for nuclear-waste storage.