When a pinch is problematic: Detecting pertechnetate in groundwater
PNNL develops an effective tool for measuring a tricky contaminant
PNNL develops an effective tool for measuring a tricky contaminant
Imagine trying to detect and measure a pinch of salt in an Olympic-size swimming pool. Now pretend the tools you are using don’t work well. Some can detect the salt but can’t tell you how much is in there, and others confuse salt with chlorine.
Now swap the swimming pool for a source of groundwater and the salt for a radioactive contaminant called pertechnetate.
Pertechnetate is a byproduct of nuclear waste. If it ends up where it is not supposed to be—like, in groundwater—it could impact human health, which is why researchers and regulators keep a close lookout for it. The environmental safety limits for pertechnetate are roughly equivalent to a pinch of salt in an Olympic pool. And there are only a few technologies to measure it, each with limitations.
PNNL research tackles this challenge with new technology to detect and accurately measure pertechnetate at super low levels in groundwater. This research, “Redox-Based Electrochemical Affinity Sensor for Detection of Aqueous Pertechnetate Anion,” was the cover article for the March 2020 edition of ACS Sensors (DOI: 10.1021/acssensors.9b01531).
Why it matters: The Environmental Protection Agency drinking water standard for pertechnetate is 0.000000052 grams per liter (that’s roughly 1/6000th the weight of a single poppy seed). While techniques exist for detection of pertechnetate in the environment, many have their drawbacks. PNNL’s technology can accurately measure low levels of pertechnetate in groundwater. Additionally, this proof of concept has the potential to be applied to other target contaminants simultaneously, increasing efficiency for environmental sensing.
Summary: The new technology acts like a coin counter, but at a microscopic level. It sorts one type of chemical from another, providing the total amount of a target chemical at the end. The tool uses custom probes with a gold electrode that only allows the target groundwater contaminants to stick while the other chemicals bounce off.
Sulfur likes to bind to gold and it also tends to react with pertechnetate, making sulfur-containing compounds an ideal intermediate in tool development. The sulfur sticks to the gold probe, then reacts with the pertechnetate, which forms a precipitate. The precipitate inhibits an electric current pulsing through the probe, providing an inverse measurement of pertechnetate concentration.
What’s Next: While this work was specifically focused on pertechnetate, there is potential to expand the technology to simultaneous multiple targets with the goal of increasing the efficiency of environmental measurements.
Sponsors: This research was funded by the Laboratory Directed Research and Development program at PNNL and by the Deep Vadose Zone program under the U.S. Department of Energy’s (DOE’s) Office of Environmental Management. Part of this research was performed at the Environmental Molecular Sciences Laboratory, a national user facility at PNNL managed by the DOE Office of Biological and Environmental Research.
PNNL Research Team: Sayandev Chatterjee, Meghan S. Fujimoto, Yingge Du, Gabriel B. Hall, Nabajit Lahiri, Eric D. Walter, Libor Kovarik. ACS Sensors cover illustration by Rose Perry, PNNL.
WastePD EFRC research on the glass-steel interface was published in Nature Materials
New research unravels the chemistry of how materials in the waste packages used for the disposal of high-level radioactive waste interact in deep geologic repository environments. Having a better understanding of the interactions between materials under various conditions provides more information to make waste storage performance models more robust.
“Many performance models use conservative approaches such as assuming that the steel canister walls don’t even exist or that they dissolve very fast. This study provides the opportunity to better incorporate the canister barrier in the models,” said Joseph Ryan, a PNNL materials scientist and coauthor on the paper, “Self-accelerated corrosion of nuclear waste forms at material interfaces,” published in Nature Materials.
The United States is converting highly radioactive nuclear waste, also known as high-level waste, into glass. The molten glass is poured into steel canisters for long-term storage and ultimate disposal in a geologic repository. The goal is to design waste storage and disposal systems that would remain safe for hundreds of thousands of years to come, even if they are exposed to water. Because of the extensive time span of waste storage, researchers turn to cutting-edge science to project what will happen during that time period. The data is used to inform extensive safety analyses—helping make sure the system is engineered to be compatible with the natural system so that waste remains separate from the environment.
“We can’t just do a test on a material and say, ‘That material corroded this much in 30 days and extrapolate that to a million years.’ It doesn’t work that way,” Ryan said. “At the most basic level, we try to understand the underlying chemistry of corrosion. Then, we feed that information into computer models to calculate the expected release over time.”
In this study, led by the WastePD Energy Frontier Research Center based at Ohio State University, researchers unpacked the chemistry that occurs when two materials are close together, focusing on glass-steel along with ceramic-steel interactions. This chemical situation could occur when water has percolated into the repository and has breached the steel canister, exposing the glass-steel interface to water.
When water finally breaches the waste package container, it will fill the microscopic space that forms between the solid glass and the steel canister. Chemical reactions that happen in localized and tiny microenvironments such as these can be quite different than those happening in a more open setting. In this case, this localized area can have a different chemistry than the surrounding solution, causing more corrosion than would be expected.
The researchers tested their theory in the laboratory. They pressed glass and steel together in salty liquid and kept it at 90° C (194° F) for a month. At the end of the experiment, they found differences in the width of thin layers that indicated higher corrosion between the glass-steel couple interface than in a control sample.
Why it matters: This research allows scientists to improve models that project how a disposal canister could perform in a deep geologic environment. Having a better understanding of the interactions between materials under various conditions provides more information to make the models more robust. Currently, some models project what happens to waste under the assumption that the steel canister walls do not exist. Operating under this pretext can result in higher projections of waste degradation than would likely occur when taking a conservative approach. But better understanding the chemistry of how the solid waste and the steel canister interact allows a scientifically based understanding of how the canisters behave and interact with the glass to be included in performance assessment models.
Summary: High-level waste is immobilized as glass in stainless steel canisters. On cooling, a confined crevice space forms at the stainless steel-glass interface. If the disposal canister is breached and if water can enter the steel-glass interface, it could result in anodic dissolution of the stainless steel, generating metal cations, which hydrolyze to form protons and strongly increase the local acidity. This acidic environment may locally enhance the corrosion of both the stainless steel and the glass, which leads to the release of cations from the glass. Further, the coupled corrosion may trigger the precipitation of additional secondary phases that may impact subsequent canister corrosion or nuclear glass durability.
What’s Next: While this study sheds light on the chemical interactions that occur at the stainless steel-glass interface, there are more interactions to explore. Ultimately, a better understanding of different chemical mechanisms will improve the overall performance model.
Sponsors: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award no. DESC0016584.
Research Team: Xiaolei Guo, Gerald S. Frankel, Gopal Viswanathan, Tianshu Li (Ohio State University); Stéphane Gin (CEA, France); Penghui Lei, Tiankai Yao, Jie Lian (Rensselaer Polytechnic Institute); Hongshen Liu, Dien Ngo, Seong H. Kim (Pennsylvania State University); Daniel K. Schreiber, John D. Vienna, Joseph V. Ryan (PNNL); Jincheng Du (University of North Texas)
Tethys Engineering addresses industry’s technical and engineering challenges
Marine renewable energy (MRE) has the potential to provide 90 gigawatts of power in the United States through waves and tidal and ocean currents.
To harness the ocean’s energy, the MRE industry needs to understand how to address technical and engineering challenges such as efficient power takeoff, device survivability, and grid integration.
PNNL developed Tethys Engineering in September 2019 to allow sharing resources around the deployment of devices in corrosive, high-energy marine environments. The recently launched Tethys Engineering online database includes collected and curated documents surrounding the technical and engineering development of MRE devices. Users can search and filter results to intuitively identify information relevant to developers, researchers, and regulators.
Tethys Engineering includes more than 3,000 journal articles, conference papers, reports, and presentations related to wave, current, salinity gradient, and ocean thermal energy conversion technologies. The database contains information from around the world.
The Tethys Engineering database was created as a companion to the already established Tethys website, which focuses on the environmental effects of the MRE industry.
In 2018, the US Department of Energy’s Water Power Technologies Office Marine Hydrokinetics Program directed two national laboratories, Pacific Northwest National Laboratory and National Renewable Energy Laboratory, to investigate the potential of marine renewable resources to contribute the U.S. electric system. Due to the innovative nature of marine renewable energy and the transformation of the US electric system resource mix, there is a lack of insight about the future potential role and grid value proposition of marine energy.
An initial step in this technical project is to review available literature to inform and help characterize the portfolio of potential marine energy resource contributions. This literature review summarizes the energy fundamentals of marine resources; the performance and operational characteristics of energy conversion devices; grid opportunities and integration challenges most applicable to marine energy; storage coupling to achieve grid opportunities; and offshore wind energy competition and collaboration. It provides the context and the state of knowledge in which the grid value proposition of marine energy should be further researched and explored.
Notable findings from the review include the following:
As the marine energy industry grows, there is a corresponding increase in the body of literature about both the potential value of harnessing marine resources as well as the requisite technical work to integrate the resource into the grid. Due to the unique aspects of marine energy resources, especially their offshore location, volume, and predictability, there are many reasons to consider marine energy a viable potential renewable resource in the future electric system.
The US Department of Energy’s Water Power Technologies Office (WPTO) has tasked two national laboratories, Pacific Northwest National Laboratory (PNNL) and National Renewable Energy Laboratory (NREL), to develop an understanding of the grid value proposition for marine renewable energy (MRE): how harnessing the energy of waves, tides, and ocean currents could be a meaningful and competitive source of renewable energy in the future grid.
This work will provide insights to the conditions under which MRE technologies offer unique benefits for the electricity system. PNNL and NREL will conduct a project to comprehensively review the grid value for marine renewable energy development at scale on an intermediate- to long-term horizon. The project will dovetail with nationally-accelerating valuation efforts to characterize and quantify specific services from energy resources and assess the value of those services over time. It will capitalize on the emerging concept of locational value, especially for distributed energy resources (DER), referencing adopted frameworks and related laboratory analysis. And it will take advantage of laboratory expertise in a variety of disciplines – ocean physics, mechanical and electrical engineering, energy economics – chained together in order to ensure that benefits and services assessed are realistic for MRE technologies and ocean energy resources.
The purpose of the immediate analytical approach is to outline the landscape of MRE attributes and their potential value and, at a high-level, discuss methods to quantify these values. For purposes of this investigation, the words grid value should be broadly construed. The term is meant to include, but not be limited to, provision of a defined grid service, measurable benefit to grid performance, avoided costs to system investments or operations, revenue capture, and contribution to desired grid qualities (e.g. reliability or low carbon intensity). Value can also accrue to a range of entities.
The authors intend to consider use cases and system benefits where MRE may have a competitive or unique role; and where there is a distinct and measurable value additional to energy production. To do this, the authors look beyond the typical values of energy production (a payment of cents per kilowatt-hour produced) and instead to “grid services,” those services required for the grid to operate and deliver energy to customers (i.e. unit scheduling and dispatch, reactive power and voltage control, and frequency control). Certain grid services are captured in the traditional suite of ancillary services that may be directly compensated in an organized market, and as a result many of these benefits already have highly competitive contributing generators or other electricity system assets. Therefore, in this initial exercise of considering competitive and unique benefits, the authors are less concerned with the energy (or grid service) production itself but the timing, the location, or the system condition that form measurable and distinct value.
During the first Wind Forecast Improvement Project (WFIP) new meteorological observations were collected from a large suite of instruments, including wind velocities measured on networks of tall towers provided by wind industry partners, wind speeds measured by cup anemometers mounted on the nacelles of wind turbines, and by networks of Doppler sodars and radar wind profilers. Previous data denial studies found a significant improvement of up to 6% RMSE reduction for short-term wind power forecasts due to the assimilation of all of these observations into the NOAA Rapid Refresh (RAP) forecast model using a 3dvar GSI data assimilation scheme. As a follow-on study, we now investigate the impacts of assimilating into the RAP model either the additional remote sensing observations (sodars and wind profiling radars) alone, or assimilating the industry provided in situ observations (tall towers and nacelle anemometers) alone, in addition to the standard meteorological data sets that are routinely available. The more numerous tall tower/nacelle observations provide a relatively large improvement through the first 3-4 hours of the forecasts, which however decays to a negligible impact by forecast hour 6. In comparison the less numerous vertical profiling sodars/radars provide an initially smaller impact that decays at a much slower rate, with a positive impact present through the first 12 hours of the forecast. Large positive assimilation impacts for both sets of instruments are found during daytime hours, while small or even negative impacts are found during nighttime hours.
Wilczak J.M., J. Olson, I. Djalaova, L. Bianco, L.K. Berg, W.J. Shaw, and R.L. Coulter, et al. 2019. "Data Assimilation Impact of In Situ and Remote Sensing Meteorological Observations on Wind Power Forecasts during the First Wind Forecast Improvement Project (WFIP)." Wind Energy 22, no. 7:932-944. PNNL-SA-132499. doi:10.1002/we.2332