H11A-0145 INVITED
Overview of NRC's Regulatory Perspective on Performance Confirmation
Regulations governing the disposal of high-level radioactive waste at 10 CFR Part 63, Subpart F, require the implementation of a Performance Confirmation Program for a geologic repository at Yucca Mountain, Nevada. The goals of the Performance Confirmation Program are to confirm that the (i) actual subsurface conditions and potential changes in these conditions during construction and waste emplacement operations are within the limits assumed during the licensing review, and (ii) natural and engineered barriers are functioning as intended and anticipated. For a license application for construction authorization, only a plan is required by the regulations. Proposed activities might include (i) monitoring the repository environment, both engineered and natural components, (ii) field and laboratory investigations under more controlled conditions to better understand processes, and (iii) scientific and programmatic evaluation of the data to support operational decisionmaking and guide adaptive design alterations. NRC review of vadose zone monitoring methods revealed limitations in current technological solutions such that many presently available hydro-environmental sensors would likely not be suitable for long- term, deep-subsurface, fractured rock monitoring activities, particularly with respect to the temperatures and radiation environment that will occur near or within waste emplacement drifts. Sensor deployment strategies will also have to be developed considering the repository environment. Thus, achieving the goals of the performance confirmation program could be affected by limits on sensor capabilities or on an as yet to be proposed sensor deployment strategy. A performance confirmation program implemented over a lengthy operational period allows for future evolution and development of sensors and strategies to further advance the collection of information relevant to processes important for performance of the potential repository at Yucca Mountain. The NRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of a license application for a geologic repository at Yucca Mountain.
H11A-0146 INVITED
A comprehensive data qa/qc strategy for data from autonomous point sensors: design, implementation and examples
There is an exponential increase in the use of autonomous point sensors (sensors which collect and transmit data without any human intervention) across all of geosciences. Point sensors include both physical and chemical sensors. Such data is typically stored in relational databases, from which data is subsequently polled for a range of different purposes. One of the fundamental challenges for end users is to assess the confidence in specific measurements. Historically (when sensor owners, sensor installers, data managers and data users were associated with one research group or institution) there might have been an intuitive (if poorly quantifiable) feel for such confidence. However, in the current environment these roles are often filled by people who are geographically separated and in different organizations. In addition, while historically such data was subject to semi manual review, this is becoming less and less practical. Finally, there is more and more a desire to use data in near real time. Consequently, challenges exist on how to automate all aspects of data qa/qc and validation for autonomous sensors. Data validation can result either in a confidence range and/or a Boolean indicator (good/bad data). We have developed and implemented a comprehensive, multi level data validation strategy. This strategy progresses from analysis of the most recent data received from a sensor (typically one to hundreds of measurements) to an analysis of the recent data in the context of the historic data received from the sensor, to an analysis of data received by other sensors (which compares trends and patterns), to a simple model based analysis. The outcome of this analysis (which is performed as soon as new data arrives) results in a quality indicator which is made available to the user with the data. In this talk I will provide examples of this approach for a number of currently operating monitoring networks as well as a discussion on how to easily implement this strategy for existing point sensor networks.
H11A-0147 INVITED
A Monitoring Platform for Deployment of Sensors for the Hydrogeologic Characterization and Monitoring of Geologic Repositories
Careful and detailed monitoring of hydrogeologic conditions in the subsurface is challenging in any case, but often extremely challenging at the greater depths and in the low-permeability environments typically required for geologic repositories. Much of the recent technological effort associated with deep hydrogeologic characterization has centered on visualization, interpretation and extrapolation of sparsely-arrayed data points; and the data points themselves often come with issues related to quality or defensibility. Such an approach is clearly inadequate to meet the demands and requirements of characterization and risk assessments suitable for deep underground repositories. Perhaps surprisingly some aspects of field procedures and instrumentation used for hydrogeologic studies have seen only slight advances over several decades. However, in other areas significant advances have been made, shedding new light on groundwater behavior and in turn driving further development of the instrumentation and procedures used for characterization and monitoring. This paper discusses some of the challenges of characterizing and monitoring deep, low-permeability groundwater environments. In particular, a technology is described that enables the deployment of a network of pressure/temperature sensors at multiple depths in the subsurface, collection of fluid samples, and execution of a variety of hydraulic tests. The technology is well suited to the deep, low permeability conditions associated with repository projects. Modular monitoring zones can be placed with almost limitless adaptability to subsurface conditions. The system serves as a reliable platform for deployment of retrievable sensors which in most cases have the capability for in-situ calibration checks. Development and advancement of this technology has continued and accelerated through almost 30 years of use on a significant proportion of the geologic repository research projects around the world. Applications have ranged to 1,200 m and more in depth and projects have included the Yucca Mountain Project in the USA, Atomic Energy of Canada's URL in Canada, the Sellafield PNWR in the UK, ANDRA's URL at Bure in France, Japan Atomic Energy Agency's URLs at Mizunami and Horonobe, and sites in South Korea. Results (including long-term monitoring, construction monitoring, data filtering for earth tide analysis, cross-well testing, etc.) from some of these projects will be presented along with a discussion of the evolution of the monitoring technology, lessons learned, current limitations, and a look toward possible future developments.
H11A-0148
Hydrologic Monitoring in the Deep Subsurface to Support Repository Performance
The INL has installed and operated several vadose and ground water monitoring systems in arid and humid sites to depths of about 200m. Some of these systems have been in continuous operation for over 12 years. It is important that the systems be physically robust, simple, yet versatile enough that it can operate for extended time periods with little or no maintenance. Monitoring instruments are frequently installed and run to characterize the site, collect data during site operation, and continue to run for long-term stewardship, necessitating sensors that can be maintained or serviced. Sensors are carefully chosen based on the perceived data requirements over the life of the site. An emphasis is given on direct measurements such as tensiometers (portable and advanced), neutron probe, drain gauge, temperature, wells or sampling for fluids and gases. Other complementary data can include using TDR/capacitance, radiation detectors, and larger scale geophysical techniques (3-d resistivity and EM) for volumetric measurements. Commercially available instruments may have to be modified for their use at greater depths, to allow multiple instruments in a single borehole or to perform the intended monitoring function. Access tubes (some open at the bottom) can be placed to allow insertion of multiple sensors (radiation, neutron and portable sensors/samplers), future drilling/sampling and to install new instruments at a later time. The installation techniques and backfill materials must be chosen and the measurement technique tested to ensure representative data collection for the parameters of interest. The data collection system can be linked to climatic data (precipitation, barometric pressure, snow depth, runoff, surface water sources) that may influence the site's subsurface hydrology. The instruments are then connected to a real-time automated data collection system that collect, stores, and provides access to the data. These systems have been developed that allow easy access, automatic data quality checks with notification, processing, and presentation of the data in real time through the web. The systems can be designed to manipulate/test the system remotely. Data from several sites will be presented showing that continuous monitoring is necessary to detect rapid changes in the deep vadose zone and ground water at fractured rock sites.
H11A-0149
Advances in Determining Soil Matric Potential Using an Engineered Porous Ceramic and Dielectric Permittivity
Soil water potential is a key parameter for determining water availability for plant growth, water flow, and soil stability. Although an in situ measurement of matric potential has been the focus of considerable research over the years, existing solutions still have many draw backs such as high maintenance, limited longevity, individual calibration requirements, high cost, and small measurement range. The objective of this research was to develop a sensor that could be used in the field to accurately measure soil matric potential without the limitations noted above. The sensor, which consisted of a dielectric sensor sandwiched between porous ceramic, was tested over a range soil types, electrical conductivties, and temperatures to calibrate and characterize its output. Data show consistent calibration curves between sensor output and actual soil matric potential over a variety of soil textures and electrical conductivities. Although temperature showed an effect on sensor output, it was low compared to overall sensor output. Likewise, salt effects were not visible in saturated matrices up to 10 dS/m. Data suggest the sensor will be an effective and robust tool to determine in situ matric potential.
H11A-0150
Taking the superconducting gravimeter to the field for hydrologic and other investigations
We have adapted the GWR superconducting gravity meter to a transportable configuration for field studies in support of hydrologic and other investigations. The gravimeter has a precision in the 10-nanogal range, and a nominal drift of a few microgals per year. Although the GWR instrument has been in production for about three decades, operations have been restricted previously to laboratory and vault environments. A ground water gravity signal has often been apparent, but complex hydrologic conditions have made quantitative interpretation difficult. By making the instrument transportable, one is able to choose sites where better-defined hydrologic problems can be investigated, and to consider tectonic, volcanic, and other applications. Technical advances have reduced the size of the helium dewar and solved the helium replenishment requirement via a compact refrigeration system. With the ability to cool to 4 K, it is possible to maintain a full dewar indefinitely. With support of NSF EAR Instrumentation and Facilities, we procured a GWR gravimeter and developed the system to be transportable, self contained within two enclosures, and accessible via cell-phone internet service. A bracket system allows the helium dewar containing the gravity sensor to be locked to the frame and transported without disassembly. Initial application is to hydrologic investigations in karst and desert alluvial aquifers. The goal is to understand hydrologic signals at a level near one microgal, equivalent to the attraction of a 2cm layer of water. Instrument precision exceeds this, but the variety of sources in the atmosphere makes it difficult to identify hydrologic signals with greater precision. Companion weather and well observations are used to observe and interpret gravity variations in terms of infiltration and storage changes, and GRACE satellite gravity observations enable separation of regional and local influences.
H11A-0151
Sensors and Monitoring Techniques for the Deep Unsaturated Zone: Reducing Uncertainty Related to Seepage and Transport in Fractured Rock
Planning for performance confirmation of hydrologic properties and processes in a potential geologic repository for high-level radioactive waste at Yucca Mountain is a requirement stated in Subpart F of 10 CFR Part 63. An important goal of performance confirmation is to acquire information indicating whether natural and engineered barriers are functioning as intended, and whether the conditions encountered are within the limits assumed during a licensing review. Long-term monitoring of hydrologic properties and processes and in situ confirmation of design assumptions will play a key role in the safe operation of the potential geologic radioactive waste repository and in the decision to close the repository. Despite remarkable advances in cyberinfrastructure for linking sensors into spatially distributed environmental networks, the extended time horizon (decades to hundreds of years) for long-term monitoring activities, the harsh thermal and radiative conditions in the near-field environment, the deep fractured unsaturated rock environment at Yucca Mountain, the potential scope of observations, and restricted access to observation ports for maintenance and upgrades each present unprecedented challenges to the design of hydro-environmental monitoring networks. Activities for performance confirmation could include the use of pore water samplers and sensors for measuring water content, matric potential, temperature, relative humidity, and water and gas fluxes. Current sensor technology for deep fractured rock systems (i) lags behind environmental observatory network solutions for surface and near-surface processes, (ii) lags behind analogous technology for unconsolidated porous media, (iii) cannot be reliably deployed without ongoing maintenance or replacement at relatively frequent intervals, and (iv) is not designed to withstand harsh thermal and radiative conditions. Long-term monitoring could require special design considerations, such as measurement redundancy, built-in self-calibration and quality assurance measures, a staged and upgradable monitoring network design, and a focused initiative for development of appropriate technologies. Safe repository operation and long-term stewardship call for concerted efforts to advance sensor technology and for strategic planning to overcome these challenges. This paper is an independent product of the CNWRA and does not necessarily reflect the view or regulatory position of the NRC. The NRC staff views expressed herein are preliminary and do not constitute a final judgment or determination of the matters addressed or of the acceptability of a license application for a geologic repository at Yucca Mountain.