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Improving nuclear waste storage models by studying the chemistry of material interactions

A female researcher wearing a blue lab coat and heat-resistant safety gloves pours molten glass out of a metal crucible onto a metal tray.

PNNL conducts research into glass, glass-ceramic, grout, metal, and metal-ceramic wasteforms that will withstand corrosion over geologic time.

PNNL | Andrea Starr

WastePD EFRC research on the glass-steel interface was published in Nature Materials

February 3, 2020
February 3, 2020
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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.

Acknowledgements

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)

January 27, 2020
DECEMBER 4, 2019
Web Feature

A More Painless Extraction

PNNL and Argonne researchers developed and tested a chemical process that successfully captures radioactive byproducts from used nuclear fuel so they could be sent to advanced reactors for destruction while also producing electrical power.

Protecting climate-sensitive soil ecosystems

Image of permafrost landscape

Review paper summarizes the effects of climate change on soil microorganisms and the ecosystem services they provide, and evaluates potential mitigation measures.

October 14, 2019
October 14, 2019
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The Science
Researchers from Pacific Northwest National Laboratory reviewed the current state of knowledge about the impacts of climate change on soil microorganisms in different climate-sensitive soil ecosystems. They also examined the possibilities of using soil microorganisms to store carbon or inoculate plants to help mitigate the negative consequences of climate change. Based on their review, the authors recommend an integrated approach that combines beneficial properties of soil microorganisms with sustainable soil management practices to support plant production, maintain a clean water supply, sustain biodiversity, store carbon, and increase resilience in the face of a changing climate.

Research showed that microbial physiology largely determines the ability of soil ecosystems to adapt to climate change, and that some microbiomes may be suitable for mitigation measures such as carbon sequestration and plant inoculation.
Research showed that microbial physiology largely determines the ability of soil ecosystems to adapt to climate change, and that some microbiomes may be suitable for mitigation measures such as carbon sequestration and plant inoculation.

The Impact
The effects of climate change on soil microbial communities have potentially large consequences for Earth's soil ecosystems and the beneficial services that soil microbiomes provide. This review highlights the need to connect the fine-scale details arising from microbiome studies to the landscape-scale resolution of many Earth system climate models in the search for climate change mitigation measures.

Summary
On Earth’s terrestrial surface, the soil microbiome cycles nutrients to sustain plant and animal life. While this microbial community is innately connected to environmental conditions, impacts on the soil microbiome due to climate change vary depending on the ecosystem. Different aspects of climate change impact soil microbial communities and their important ecosystem functions, such as cycling of carbon and supporting plant growth. But the molecular details of soil biochemical reactions responsible for these key functions are largely unknown.

Researchers synthesized existing knowledge of climate change impacts across a range of soil environments—permafrost, forests, grassland, wetlands, and deserts—to examine how the microbiome responds. They looked at microbial changes coinciding with different climate change variables including increases in carbon dioxide levels, temperatures, drought, flooding, and fires. Their review showed that microbial physiology largely determines the ability of soil ecosystems to adapt, and that some microbiomes may be suitable for climate change mitigation measures such as carbon sequestration and promoting plant growth. The review sets the stage for future research on soil microbiomes and challenges to overcome in order to connect to larger-scale predictive models of climate change.

Contacts
Janet Jansson, Lab Fellow, janet.jansson@pnnl.gov
Kirsten Hofmockel, Earth Scientist, kirsten.hofmockel@pnnl.gov

Funding
This research was supported by the Department of Energy Office of Biological and Environmental Research (BER) Genomic Science Program and is a contribution of the Scientific Focus Area "Phenotypic response of the soil microbiome to environmental perturbations." PNNL is operated for DOE by Battelle Memorial Institute under Contract DE-AC05-76RLO1830. A portion of the research was performed using the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility sponsored by BER and located at PNNL.

J. Jansson and K.Hofmockel, “Soil microbiomes and climate changeNature Reviews Microbiology, 04 October 2019. [DOI: 10.1038/s41579-019-0265-7]

Top Ten Blendstocks for Turbocharged Gasoline Engines

Cover of Co-Optima Report

Bio-blendstocks with the potential to deliver the highest engine efficiency

October 8, 2019
October 8, 2019
Report

More efficient engines enabled by better fuels could increase the fuel economy of light duty (LD) vehicles by 10 percent beyond current technology and planned developments. This report identifies top blendstocks that can be derived from biomass and are suitable for further development and commercialization. These blendstocks are best-suited for LD gasoline, boosted spark ignition (BSI) engines. The blendstocks were identified using a fuel property basis using the BSI merit function. The merit function determines potential improvements in engine efficiency, was used to evaluate the performance of candidate bioblendstocks in blends up to 30%. Those that exceeded the efficiency of an E10 premium were included in this list. This report is aimed at biofuel researchers looking to better understand the efficiency implications of biofuels under development, as well as engine researchers who are interested in future biofuels with properties that enable more efficient engine design and operation.

The Co-Optimization of Fuels & Engines (Co-Optima) team includes experts from nine national laboratories: Argonne, Idaho, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge, Pacific Northwest, and Sandia National Laboratories and the National Renewable Energy Laboratory. The team’s expertise includes biofuel development, fuel property testing and characterization, combustion fundamentals, modeling and simulation from atomic scale to engine scale, and analysis.

Gaspar, Daniel J., West, Brian H., Ruddy, Danial, Wilke, Trenton J., Polikarpov, Evgueni, Alleman, Teresa L., George, Anthe, Monroe, Eric, Davis, Ryan W., Vardon, Derek, Sutton, Andrew D., Moore, Cameron M., Benavides, Pahola T., Dunn, Jennifer, Biddy, Mary J., Jones, Susanne B., Kass, Michael D., Pihl, Josh A., Pihl, Josh A., Debusk, Melanie M., Sjoberg, Magnus, Szybist, Jim, Sluder, C S., Fioroni, Gina, and Pitz, William J. Top Ten Blendstocks Derived From Biomass For Turbocharged Spark Ignition Engines: Bio-blendstocks With Potential for Highest Engine Efficiency. United States: N. p., 2019. Web. doi:10.2172/1567705.

Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions

Image of Peatland forest

Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures.

October 3, 2019
October 3, 2019
Highlight

The Science
As atmospheric temperatures and carbon dioxide concentrations rise, photosynthesis by plants is expected to increase, leading to more photosynthate released by roots to the soil microbial community. Researchers from Pacific Northwest Northwest National Laboratory and Iowa State University examined the response of boreal peatland soils under future high temperatures. The team found that the peatland’s soil microbial communities allocated more carbon to enzyme production in search of phosphorus as temperatures climbed. This diversion of carbon resources could reduce future carbon losses by microbial respiration from the peatland.

The Impact
As boreal peatlands face warmer and drier conditions, it is expected that more carbon will be lost from these carbon-rich soils through increased microbial activity. This study showed that enhanced respiration and concomitant loss of carbon is potentially constrained by nutrient demands of the microorganisms. This tradeoff may help the peatland ecosystem retain soil carbon as temperatures warm.

Summary
Root exudates are carbon compounds, such as sugars and organic acids, which are easily consumed by soil microorganisms. With a warming climate, science suggests that increased photosynthesis by plants could lead to more photosynthate released as root exudates to the soil microbial community. To examine this question, researchers used laboratory incubations to control both temperature and moisture and simulate belowground substrate additions under an accelerated growing season. Results showed that with a moderate increase in temperature, the addition of common root exude compounds in peatlands initially increased carbon lost through microbial respiration above those treatments receiving water only. However, when pushed to future expected high temperatures, additional exudate compounds dampened the amount of additional carbon respired as compared to treatments receiving water only. This reduction in respiration suggests the microorganisms allocated carbon compounds to enzyme production to mine for limited resources instead of respiring carbon. The data also support the idea that boreal peatland microbial communities maintain a more narrow range in function, measured as respiration, across a range in climate conditions. A wide climatic niche in addition to reallocation of carbon resources dampens the magnitude of change in carbon respiration with increasing temperatures.

Contact
Kirsten Hofmockel
Biological and Environmental Scienes Directorate
kirsten.hofmockel@pnnl.gov

Funding
This material is based upon work supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program, under grant ER65430 to Iowa State University.

Keiser, A.D., Smith, M., Bell, S. & Hofmockel, K.S. Peatland microbial community response to altered climate tempered by nutrient availability. Soil Biology and Biochemistry 137, 1-9, (2019).