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International Nuclear Waste Disposal Research Effort Evaluates Maximum Allowable Temperature for Bentonite Buffer2 min read

by Christina Procopiou on September 28, 2021

Energy Geosciences Division

Above: key construction milestones of the field test with two sectors that are separated by retaining walls.

Around the world in the many nations where nuclear power is used, isolating nuclear waste deep underground is deemed as the viable permanent solution. Geological repository for high-level nuclear waste, the type of nuclear waste created by the reprocessing of spent nuclear fuel, is usually a multi-barriers system that includes waste packages, engineered barrier system (EBS), and host rocks. One of the most important design variables for a repository is the temperature limit up to which the EBS and the natural geologic environment can be exposed.

Up to now, almost all design concepts that involve bentonite-backfilled emplacement tunnels have chosen a maximum allowable temperature of about 100 °C. However, whether bentonite can sustain higher than 100 °C is still an open question and  raising maximum allowable temperature will significantly lower the cost of repository. In new research inspired by a 2015 study from Berkeley Lab geoscientists, an international collaboration has taken a big step towards studying how bentonite will perform under the influence of long-term high temperature heating. 

Represented by these Energy Geosciences Division experts, the Department of Energy is one of five major partners in the “HotBENT” project led by Nagra, the centerpiece of which is long-term field test of a bentonite buffer heated to 175-200  °C at the Grimsel Test Site in Switzerland. After focusing more than a year on constructing the field test at this underground rock laboratory, this month the team began heating the bentonite buffer and will reach 200 °C in about two months, much higher than that of previous tests at any field test site anywhere in the world. 

Staff scientist LianGe Zheng who leads Berkeley Lab’s participation in the collaboration said, “The concern is that when nuclear waste emits a lot of heat it will change both the geophysical and geochemical properties of bentonite buffer and host rock. For this long-term series of experiments, the objective is to evaluate the thermal, hydrological, chemical, and mechanical (THMC) changes in the EBS bentonite and how that affects the bentonite barrier’s safety function over time.”

For five years the team will monitor how the bentonite buffer in one of the two sectors behaves in response to simulated heating to shed light on whether bentonite can withstand heating at temperatures higher than 100  °C. Then they will dismantle this sector to take samples for  geochemical measurements and final check of THM properties . The collaborators will continue monitoring the other sectors for probably an additional 15 years to evaluate even longer term THMC over time. 

Zheng and his colleagues at Berkeley Lab had been actively participating in the project since the very beginning, supported the design of the test with numerical models, and will contribute to the project using the coupled THMC model to predict bentonite evolution and interpret the data collected during the monitoring period. 

 

 

News & Events

EESA Research Scientist Selected for NAE 2022 U.S. Frontiers of Engineering Symposium2 min read

May 23, 2022

Mengsu Hu, an EESA research scientist, was selected to participate in the National Academy of Engineering (NAE) U.S. Frontiers of Engineering symposium in September. For more than 25 years, the NAE has identified the best and brightest early-career engineers from large and small companies, research universities, and government laboratories to discuss their leading-edge research and…

Microbial Response to a Changing and Fire-Prone Arctic Ecosystem2 min read

April 27, 2022

Burning more than 1,000 square kilometers of tundra on Alaska’s North Slope, the 2007 Anaktuvuk river wildfire is one of the largest fires to occur within Arctic ecosystems. Berkeley Lab scientist Nick Bouskill led a study that used data from this disturbance event to predict ecosystem recovery as fires advance in a changing climate. (Credit:…

Study Evaluates Phosphorus Availability Underground using Plant Leaves as Biosensors3 min read

April 25, 2022

When envisioning renewable energy, sources that often come to mind are the sun, wind, batteries, and water. However, biofuel, a type of renewable energy that converts organic material from plants into liquid fuel, is an important part of a global effort to achieve net-zero emissions. Switchgrass, a deep-rooted native North American grass that grows in…

EESA Multimedia Producer and Digital Strategist Niba Audrey Nirmal Awarded Ocean Science Journalism Fellowship1 min read

Niba Audrey Nirmal, EESA Multimedia Producer and Digital Strategist, has been awarded the Woods Hole Oceanographic Institute (WHOI) Ocean Science Journalism (OSJ) Fellowship.   In May, Nirmal will join nine other selected fellows on a five-day, experiential-learning based retreat at the WHOI located in Falmouth, Massachusetts to learn about ocean-science concepts ranging from marine biology to…

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