Radiochemistry intern digs deep to prevent the spread of nuclear waste

The groundbreaking discoveries and scientific advancements that take place at Lawrence Livermore National Laboratory (LLNL) and ­­across the broader national laboratory system rely on the passage of information from tenured staff scientists to new interns and early career scientists.

This past summer, Zachary (Zach) Murphy, a Ph.D. student studying chemistry at the University of Central Florida, interned with LLNL’s Glenn T. Seaborg Institute under the mentorship of Gauthier Deblonde, a radiochemist for the Nuclear and Chemical Sciences Division.

“Despite there being a persistent and global demand for radiochemists, there has been a decline in those entering the field,” Deblonde said. “Providing young and motivated students like Zach the opportunity to conduct research alongside Livermore staff scientists is key to bridging knowledge gaps in radiochemistry.”

Murphy’s summer research focused on evaluating an organic-rich rock formation: characterizing which minerals are present and how radioactive elements interact with different rock layers. This work is a part of a larger, ongoing project to evaluate new locations for a potential nuclear waste repository used to store legacy waste deep underground. The ideal repository site would have natural barriers to stop the nuclear waste from spreading into the environment since engineered barriers (such as metallic canisters) slowly break down over time due to corrosion and other natural phenomena. 

Prior to Murphy’s internship, the research team drilled more than 100 meters underground to collect five core samples at different depths and two representative surface samples that had been exposed to environmental conditions.

Over the course of his 10-week internship, Murphy ran hundreds of leach and sorption tests with these samples — mixing rock powder with water, plus radioactive elements in some cases, and then analyzing which organic compounds are released by the rocks (leach tests) and how radioactive elements stick to the rocks (sorption tests). Underground organic compounds like carbohydrates, lipids, proteins and nucleotides come from organic matter consisting of plant/animal tissue in various stages of decomposition. The team suspects that the natural compounds released from the rocks may interact with the waste and impact the radioactive elements’ mobility in the environment.

These tests are similar to brewing coffee, where water is run through the coffee grounds, leaving the grounds behind but taking the caffeine content with it. Except, in these experiments, researchers want to measure which sample releases the smallest amount of organic compounds into the surrounding water. In this analogy, a light coffee is better than a strong one.

For the leach tests, Murphy mixed the rock sample with water, and then separated the two layers from each other, to measure how much organic matter is being released into the aqueous layer. His analyses reveal that, generally, rocks closest to the surface leave the most organic matter in the water, while deeper rocks leave the least amount. Surprisingly, it also was found that depth and amount of organic matter, as well as the nature of the compounds, do not directly correlate.  

For the sorption tests, Murphy spiked the water with a radioactive isotope typically present in nuclear waste (examples include neptunium, plutonium, americium, curium, etc.), and then separated the two layers to see if the isotope sticks to the rock sample or remains in the water. To avoid contamination, it is preferred for the isotope to stick to the rock so that it is not released into the water.

From these experiments, the team can make recommendations as to which rock layer is best for a nuclear waste repository. That is, researchers can determine if rock depth and/or rock composition affect whether radioactive elements stick to the rock or mix with the water and what role soluble organic matter plays in these results.

“It has been great to get some radioactive material experience and to use the cool analytical techniques that are available at the Livermore Lab,” Murphy said. “It has even given me a lot of ideas and directions to explore further in my Ph.D. work.”

At the University of Central Florida, Murphy’s research is in the same vein as his LLNL work: looking at the mobility of uranium in the environment. Except his university research focuses on how certain chemical compounds, known as chelating agents, may make elements like uranium more mobile, enhancing their migration at disposal sites.

Aside from his Livermore research, Murphy expressed how fun it was to visit California for the first time. He said: “Driving to Yosemite and seeing the beautiful views was definitely a highlight of this experience.”  

– Shelby Conn