Researcher tracks uranium isotopes

You’d think, after a couple million years, the trail might have gone cold. In fact, it’s just heating up for Sue Clark.

 

As an internationally recognized environmental radiochemist, Clark devises techniques for measuring uranium and other radioactive
elements in soil and water. Her methods not only help monitor global nuclear activity but also can trace isotopes from ancient, naturally occurring “fission reactors” formed many millennia ago.

 

Clark is a WSU chemistry professor and interim vice-chancellor for academic affairs at WSU Tri-Cities. She and her students are contributors to the field of nuclear forensics. Using science laboratories and the Nuclear Radiation Center at WSU Pullman, and through collaborations with the Pacific Northwest National Laboratory in the Tri-Cities, the team develops analytical procedures necessary to monitor environmental evidence of nuclear activities.

 

In a world grappling with nuclear proliferation and dwindling energy supplies, nuclear forensics could be seen as a foreboding sign of the times. But Clark sees it as an exciting time of possibility and promise.

 

Clues in the isotopes
Radiochemistry is a branch of chemistry devoted to the study of radioactive elements such as uranium and plutonium. For Clark, it is the isotopic distribution of each element that is most fascinating.

 

Uranium, for example, is commonly found in rocks, dust, walls, carpet, etc. But only a certain distribution of those uranium isotopes is naturally occurring — such as U-238, which accounts for more than 99 percent of the isotopic distribution. U-235 — the potentially fissile type of uranium — makes up less than one percent.

 

When U-235 is enriched and burned as fuel in a fission reactor, the natural isotopic distribution is changed, leading to the creation of other isotopes such as U-233, U-236 and plutonium. According to Clark, this isotopic distribution acts as a “signature” showing where the soil or water sample has been and what has happened to it over the short term or on a geologic timescale.

 

“You can see evidence of this along the Columbia River,” said Clark. “If you check the isotopic distribution of uranium above and below the Hanford site, you will see differences. Even though Department of Energy (DOE) reactors are not operated there today, you can find isotopic signatures of past site activities in the sediments below Hanford.”

 

Learning from the past
The isotopic signature also can give information about prehistoric nuclear activity, as seen in the Oklo fossil reactors in Gabon, West Africa. Scientists discovered that uranium ore from the Oklo deposits had an isotopic signature resembling that of used nuclear fuel from power plants. It was theorized that high amounts of U-235 in the ore had triggered spontaneous fission reactions.

 

Yet even after 2 billion years, most of the “nuclear waste” at Oklo has been effectively contained by rock formations — with plutonium isotopes moving only feet from their original site.

 

 

Today, the mines serve as a natural model for nuclear waste containment, providing clues for solving the problems associated with large-scale nuclear energy use. Although nuclear power provides only 20 percent of U.S. energy needs, it is an important option for sustainable alternatives for energy independence.

 

Recycling uranium
In 2006, President George W. Bush created the Global Nuclear Energy Partnership — with the goal to build an international coalition for recycling used nuclear fuel in a way that reuses key components but sequesters the plutonium isotopes that could be used for nuclear weapons.

 

As part of that initiative, chemistry professors Kenneth Nash, Pat Meier and Clark last fall received a $3 million DOE Nuclear Energy Research Initiative (NERI) grant to investigate methods for reprocessing used nuclear fuel.

 

The team is studying the process of separating used fuel byproducts from the energy-producing uranium. The byproducts are then “transmuted” by irradiation into shorter-lived isotopes.

 

Developing separations to recycle uranium could provide a timely solution for radioactive waste disposal. But Clark cautions, “There are still many years of research and development that need to be done before the U.S. as a nation can use the transmutation technology.”

 

In the meantime, the NERI grant also provides funding for training students in nuclear science.

 

“One of the problems with increasing the energy portfolio in the U.S. is a lack of skilled person-power,” said Clark. “There are not enough students trained in this area … and earlier researchers from the days of the Manhattan Project are retiring.”

 

Clark is hopeful that the radiochemistry program at WSU, together with a consortium of four other universities, will create a pipeline for bringing students into the field.

 

“It’s an exciting time to be involved in this type of work,” she said. “There are tremendous challenges that we will have to overcome as a nation. And this requires that we have bright young people who are excited and engaged to work on these problems.”

 

Paving the way for women in science
Get her talking about radiochemistry and Sue Clark lights up with enthusiasm — affirming her reputation as a compelling mentor in the department of chemistry. Hired in 1996, Clark became a full professor and the first woman to chair the department.

 

“I would not be where I am today if it had not been for Sue’s guidance and influence,” said one of Clark’s former graduate students, Rosi Payne, who works as a radiochemist at Pacific Northwest National Laboratory.

 

“Having women faculty members makes a big difference in students’ perception of the chemistry program,” said Mike Griswold, College of Sciences dean.

 

Only 235 women have attained the rank of full professor of chemistry in the U.S., said Jim Petersen, engineering professor and former vice provost for research.

 

He acknowledged Clark’s role as a mentor for both male and female faculty and graduate students — adding that she also promotes the national and international reputation of WSU.

 

“She has traveled throughout the world to advise the DOE regarding nuclear power and national security,” he said.

 

She also has helped him understand the importance of leadership and support provided by senior male faculty. “A single supportive comment by a respected male leader enables another’s views to be better heard,” he said. “Such comments can dramatically change a culture, turning a hostile meeting into one where all views are heard.”

 

To learn more about Clark’s research visit www.chem.wsu.edu/people/faculty/s_clark.html or the Global Nuclear Energy Partnership at www.gnep.energy.gov