Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Reactor research could save money on nuclear waste handling


NEW REACTOR: Sandia researcher Gary Harms conducts experiments with a new Sandia-built reactor that are paving the way toward possible changes in regulations on transport and storage of nuclear waste. (Photo by Randy Montoya)

Recent experiments by Sandia National Laboratories researcher Gary Harms and his team are using a new Labs-built reactor to provide benchmarks showing that spent nuclear fuel — uranium that has been used as fuel at a nuclear power plant — is considerably less reactive than the original fresh fuel. This could mean significant savings in the eventual safe transport, storage, and disposal of nuclear waste.

“The conservative view has always been to treat spent fuel like it just came out of the factory with its full reactivity,” Harms, project lead, says. “This results in the numbers of canisters required in the handling of spent nuclear fuel to be conservatively high, driving up shipping and storage costs.”

The more realistic view is that as nuclear fuel is burned, the reactivity of the fuel decreases due to the consumption of some of the uranium and to the accumulation of fission products, the “ash” left from burning the nuclear fuel. Accounting for this reactivity decrease, called burnup credit, would allow for the spent nuclear fuel to be safely packed in more dense arrays for transportation, storage, and disposal than would be possible if the composition changes were ignored.

“Allowing such burnup credit would result in significant cost savings in the handling of spent nuclear fuel,” Harms adds.

This seems obvious on the surface, but in the ultraconservative world of nuclear criticality safety, an effect must be proven before it is accepted. Thus, prior to the Nuclear Regulatory Commission ever agreeing to the more realistic view, it would have to be proven in actual experiments and compared to computer models showing the same effects.

In 1999 Harms obtained a three-year grant from the Department of Energy’s (DOE) Nuclear Energy Research Initiative to make benchmark measurements of the reactivity effects that fission products have on a nuclear reactor. The project was called the Burnup Credit Critical Experiment (BUCCX). Rhodium, an important fission product absorber, was chosen for the first measurements.

To do this the BUCCX team first designed and built a small reactor, technically called a critical assembly, which uses low-enriched fuel. The control system and some of the assembly hardware for the reactor came from the 1980s-era Space Nuclear Thermal Propulsion (SNTP) Critical Experiment project, designed to simulate the behavior of a nuclear rocket reactor.

The reactor, which operated during the experiments at a lower power than a household light bulb, was subjected to several layers of safety reviews. During the experiments, it performed safely exactly as predicted.

“It took us most of the three years to build the reactor and get authorization to use it. Only in the last few months have we begun actual experiments,” Harms says. “Much of the time was involved in getting approvals from Sandia and DOE and to make sure it meets all ES&H concerns.”

The core of the BUCCX consists of a few hundred rods full of pellets of clean uranium that originally came from the nuclear powered ship NS Savannah. Thirty-six of the rods can be opened to insert experiment materials between the fuel pellets. Prior to conducting experiments with the rhodium, the researchers loaded the reactor to critical with only the uranium fuel. This provided a baseline point of where uranium goes critical — information that could be compared to later experiments.

Then, the BUCCX team added about 1,200 circular rhodium foils between the uranium pellets in the 36 rods. The intent was to measure the extent to which the rhodium reduced the reactivity of the uranium.

“We then compared the critical loading of the assembly with the rhodium foils to the critical loading without rhodium,” Harms says.

And, not to anyone’s surprise, it took significantly more fuel to reach critical with the rhodium-doped rods than without them.

Months before running the physical experiments on the reactor, Harms was modeling on Sandia’s sophisticated computers to determine where the uranium doped with rhodium would go critical.

“I was curious,” Harms says, “I did calculations ahead of time so I could lay out the experiment and get a peek at what the experiments would say. In the end, I was fairly impressed with how accurate the calculations were compared to the actual physical experiments.”

Of course, the computer codes weren’t perfect, and had a small bias when compared to other criticality safety benchmarks. And in analyzing the actual experiments in the reactor, Harms took that bias into account.

Harms says two other fission products absorb neutrons better than rhodium. However, he selected rhodium to run the experiments because it is one of the few byproducts of fission that has a single stable isotope, which means the experiment would not be contaminated by the effects of other isotopes. Also, no one else has done any experiments with rhodium in a critical assembly. Subsequent experiments could address the dozen or so other fission products that are important to burnup credit.

Also, to his knowledge, no other lab in the US is doing actual burnup credit experiments. Oak Ridge National Laboratory is running codes to determine how much the reactivity of spent fuel is reduced by fission products, but not doing actual experiments.

At the end of the three-year funding period, Harms says the Sandia program has come a long way in proving that the reactivity of spent fuel is considerably less than that of fresh fuel.

“In essence Sandia is helping pave the way for the Nuclear Regulatory Commission to address the safe and cost-efficient transport and storage of nuclear waste,” Harms says.

Chris Burroughs | EurekAlert!

More articles from Power and Electrical Engineering:

nachricht Waste from paper and pulp industry supplies raw material for development of new redox flow batteries
12.10.2017 | Johannes Gutenberg-Universität Mainz

nachricht Low-cost battery from waste graphite
11.10.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>



Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

More VideoLinks >>>