Office of the Vice President for Global Communications

Tuesday, September 8, 2009

Contracts to aid study of stress on nuclear reactors

Two recent energy contracts will ensure that U-M will continue to be world-class in looking for cracks in the nuclear energy system — literally.

Two five-year contracts, totaling $2.4 million, from the Electric Power Research Institute (EPRI) and Oak Ridge National Laboratory under the U.S. Department of Energy’s Light Water Sustainability Program are enabling U-M scientists to better understand how radiation, stress and corrosion can lead to cracking in the inner workings of nuclear reactors.

That, combined with another three recent grants totaling $941,625, will continue advancing understanding of the stresses endured by nuclear reactor materials.

In a nuclear power plant, water is heated to produce steam that is then converted to electricity. The heat is created by nuclear fission – the controlled splitting of atoms to release enormous amounts of energy – millions of times more than that created by burning wood or coal, and without greenhouse gases.

Nuclear reactors are built to contain that energy — which generates tremendous heat and pressure — making wear and tear on the materials inside significant.

“It’s crucial we understand how they these materials degrade so can predict how long they can last, and how we can improve them to extend the life of existing reactors and build a new generation of advanced reactors,” says Gary S. Was, the U-M nuclear engineering professor who is principal investigator of the grant.

The cracks that Was, the Walter J. Weber Jr. Professor of Sustainable Energy, Environmental and Earth Systems Engineering, explores are tiny – about 1 micrometer at initiation, which is about 1/100th the thickness of a human hair.

Still, even tiny cracks and other damage eventually can translate to downtime, costly because power companies must then purchase electricity elsewhere. Given the aging of the U.S. reactor fleet, Was says, it’s critical to understand the status of the core’s materials.

“These reactors are outstanding sources of clean, reliable electricity,” he says. “They generate cheap power and the last thing we want to do is take them out of service, so it’s important we know how long materials will last and how to improve their performance so they can enable the reactor to safely run longer.”

U-M’s Phoenix Memorial Laboratory on North Campus has among the most advanced facilities in the nation for studying reactor materials in conditions similar to those they would experience in operating reactors – but in shorter time frames.

“We have ways to mimic conditions and effects in a much more direct and rapid manner than has been done in past,” Was says. “We have created facilities where we can immerse materials in environments similar to what they see in service, and we will evaluate their tendency to crack and the rate of growth of cracks in the same environment they see in a reactor core.”

With 104 operating nuclear plants in the United States all nearing the end of their original 40-year license, extension of the license to 60 years and perhaps even 80 years is dependent on demonstrating that they will continue to operate safely. Safe operation comes down to the behavior of materials from which they are constructed.

Key to the facility are two hot cells, rooms with concrete walls 3-feet thick. A 3-foot window of leaded glass layered with oil (to adjust the optics and improve visibility) enables researchers to safely manipulate radioactive materials from outside the cells with mechanical arms.

Mobile high-temperature autoclaves and a scanning electron microscope can be moved in to and out of the hot cells, making it possible to analyze materials that have been exposed to high radiation fields for extended periods of time. The facility consists of two autoclave-loading systems, with three more under construction.

This program builds on an international effort, aimed at the same objective, that was led by EPRI and engaged major nuclear energy institutions around the world from 1997 through 2009, Was says.

The three new grants are from the Department of Energy, Idaho National Laboratory and the National Nuclear Security Administration.