Modelling of lab and field experiments: HGA EXPERIMENT

Transport in Porous Media, 2011

In low/intermediate-level waste (L/ILW) repositories, anaerobic corrosion of metals and degradation of organic materials produce mainly hydrogen, methane, and carbon dioxide. The Swiss reference concept for the L/ILW repository consists of parallel caverns sealed off from a single access tunnel in a deep low-permeability claystone formation. The potential buildup of excess gas pressures in the backfilled emplacement caverns was investigated in a series of two-phase flow models. In the first step, a large-scale model was constructed, implementing the 3D radial tunnel and cavern geometry with a simplified rectangular geometry. In the second step, the potential impact of the detailed geometry of the engineered barrier system (EBS) and the associated heterogeneity inside the cavern was examined using detailed models of the repository caverns, tunnel seals, access tunnel, and surrounding host rock. The simulation results from the large-scale 3D repository model show that during the early post-closure period simulated pressures can vary significantly between different parts of the repository. The simulated pressure increase in the emplacement caverns

2014

In some cases there may be a milestone where an item is being fabricated, maintenance is being performed on a facility, or a document is being issued through a formal document control process where it specifically calls out a formal review of the document. In these cases, documentation (e.g., inspection report, maintenance request, work planning package documentation or the documented review of the issued document through the document control process) of the completion of the activity along with the Document Cover Sheet is sufficient to demonstrate achieving the milestone. If QRL 1, 2, or 3 is not assigned, then the Lab/Participant QA Program (no additional FCT QA requirements box must be checked, and the work is understood to be performed, and any deliverable developed, in conformance with the respective National Laboratory/Participant, DOE-or NNSA-approved QA Program.

2015

Development of an enhanced performance assessment (PA) capability for geologic disposal of spent nuclear fuel and high-level waste has been ongoing for several years in the U.S. repository program. The new Generic Disposal System Analysis (GDSA) modeling and software framework is intended to be flexible enough to evolve through the various phases of repository activities, beginning with generic PA activities in the current Concept Evaluation phase to site-specific PA modeling in the Repository Development phase. The GDSA Framework utilizes modern software and hardware capabilities by being based on open-source software architecture and being configured to run in a massively parallel, high-performance computing (HPC) environment. It consists of two main components, the open-source Dakota uncertainty sampling and analysis software and the PFLOTRAN reactive multi-phase flow and transport simulator. Reference cases or “generic repositories” have been, and are being developed, based on t...

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 2010

The Cementitious Barriers Partnership (CBP) was initiated to reduce risk and uncertainties in the performance assessments that directly impact U.S. Department of Energy (DOE) environmental cleanup and closure programs. The CBP is supported by the DOE Office of Environmental Management (DOE-EM) and has been specifically addressing the following critical EM program needs: (i) the long-term performance of cementitious barriers and materials in nuclear waste disposal facilities and (ii) increased understanding of contaminant transport behavior within cementitious barrier systems to support the development and deployment of adequate closure technologies. To accomplish this, the CBP has two initiatives: 1) an experimental initiative to increase understanding of changes in cementitious materials over long times (> 1000 years) over changing conditions and 2) a modeling initiative to enhance and integrate a set of computational tools validated by laboratory and field experimental data to improve understanding and prediction of the long-term performance of cementitious barriers and waste forms used in nuclear applications. In FY10, the CBP developed the initial phase of an integrated modeling tool that would serve as a screening tool which could help in making decisions concerning disposal and tank closure. The CBP experimental programs are underway to validate this tool and provide increased understanding of how CM changes over time and under changing conditions. These initial CBP products that will eventually be enhanced are anticipated to reduce the uncertainties of current methodologies for assessing cementitious barrier performance and increase the consistency and transparency of the DOE assessment process. These tools have application to low activity waste forms, high level waste tank closure, D&D and entombment of major nuclear facilities, landfill waste acceptance criteria, and in-situ grouting and immobilization of vadose zone contamination. This paper summarizes the recent work provided by the CBP to support DOE operations and regulatory compliance and the accomplishments over the past 2 years. Impacts of this work include: 1) a forum for DOE-NRC technical exchange, 2) material characterization to support PA predictions, 3) reducing uncertainty in PA predictions, 4) establishing base case performance to improve PA predictions, and 5) improving understanding and quantification of moisture and contaminant transport used in PAs. Additional CBP accomplishments include: sponsorship of a national test bed workshop to obtain collaboration in establishing the path forward in obtaining actual data to support future predictions on cementitious barrier performance evaluations, and participation in an International Atomic Energy Agency (IAEA) Cooperative Research Project on the use of cementitious barriers for low-level radioactive waste treatment and disposal.

2004

An integrated modeling approach was developed to investigate coupled thermal, hydrological, and chemical (THC) processes around proposed nuclear waste emplacement tunnels at Yucca Mountain, Nevada. The approach involves the development of process models, followed by numerical implementation and validation against field and laboratory experiments, then long-term predictive simulations. An existing reactive transport numerical code was refined and validated to evaluate the chemistry of waters around the tunnels and the effect of water-rock interaction on hydrological behavior around the repository. At liquid saturations significantly larger than residual, no extreme pH or salinity values were predicted. Mineral precipitation around the tunnels consists mainly of silica with minor calcite, trace zeolites and clays. The effect of mineral precipitation on flow depends largely on initial fracture porosity, and results in negligible to significant diversion of percolation around the tunnel...

2010

The Cementitious Barriers Partnership (CBP) was initiated to reduce risk and uncertainties in the performance assessments that directly impact U.S. Department of Energy (DOE) environmental cleanup and closure programs. The CBP is supported by the DOE Office of Environmental Management (DOE-EM) and has been specifically addressing the following critical EM program needs: (i) the long-term performance of cementitious barriers and materials in nuclear waste disposal facilities and (ii) increased understanding of contaminant transport behavior within cementitious barrier systems to support the development and deployment of adequate closure technologies. To accomplish this, the CBP has two initiatives: (1) an experimental initiative to increase understanding of changes in cementitious materials over long times (> 1000 years) over changing conditions and (2) a modeling initiative to enhance and integrate a set of computational tools validated by laboratory and field experimental data t...

2001

The evolution of fluid chemistry and mineral alteration around a potential waste emplacement tunnel (drift) is evaluated using numerical modeling. The model considers the flow of water, gas, and heat, plus reactions between minerals, CO 2 gas, and aqueous species, and porositypermeability-capillary pressure coupling for a dual permeability (fractures and matrix) medium. Two possible operating temperature modes are investigated: a ''high-temperature'' case with temperatures exceeding the boiling point of water for several hundred years, and a ''lowtemperature'' case with temperatures remaining below boiling for the entire life of the repository. In both cases, possible seepage waters are characterized by dilute to moderate salinities and mildly alkaline pH values. These trends in fluid composition and mineral alteration are controlled by various coupled mechanisms. For example, upon heating and boiling, CO 2 exsolution from pore waters raises pH and causes calcite precipitation. In condensation zones, this CO 2 redissolves, resulting in a decrease in pH that causes calcite dissolution and enhances feldspar alteration to clays. Heat also enhances dissolution of wall rock minerals leading to elevated silica concentrations. Amorphous silica precipitates through evaporative concentration caused by boiling in the high-temperature case, but does not precipitate in the low-temperature case. Some alteration of feldspars to clays and zeolites is predicted in the high-temperature case. In both cases, calcite precipitates when percolating waters are heated near the drift. The predicted porosity decrease around drifts in the high-temperature case (several percent of the fracture volume) is larger by at least one order of magnitude than in the low temperature case. Although there are important differences between the two investigated temperature modes in the predicted evolution of fluid

Water Pollution: Modelling, Measuring and Prediction, 1991

The hydrodynamic effects of gas release from an underground nuclear waste repository are examined using the multiphase simulator TOUGH. Pressurization of the repository is found to be strongly affected by absolute and relative permeability characteristics of the backfill material, and to a lesser extent by its air-entry capillary pressure. Analysis of worst-case scenarios indicate the creation of significant pressure gradients which could cause structural damage to the repository. The use of a vent to allow gas outflow into the near-field helps in dissipating excess pressures and establishing pressure equilibrium throughout the repository.

2015