A research team at the U.S. Department of Energy’s (DOE) Oak Ridge National Laboratory (ORNL) (Oak Ridge, Tennessee, USA) is developing what they say is a safer cladding for nuclear fuel rods. The new material, an alloy of iron, chromium, and aluminum, avoids zirconium. As a result, they believe it should give plant operators substantially more time to react to incidents like a station blackout.
The fuel rods at civilian nuclear power plants have been sheathed with an evolving Zr alloy for the past six decades, ORNL explains. Zirconium absorbs very few of the neutrons that drive a nuclear reactor, so zirconium alloys make sense as a fuel cladding—if the reactor operates as planned. If a reactor loses its cooling water, however, the zirconium alloys can bring unintended consequences.
“The issue is you have anywhere between 20 and 40 tons of zirconium metal in these reactor cores,” explains ORNL nuclear engineer Kurt Terrani, who heads up the project as part of a consortium involving General Electric (Boston, Massachusetts, USA). “Zirconium reacts with steam at high temperature, and when it reacts, it produces a lot of heat and a lot of hydrogen.”
As such, the team aimed to create a zirconium-free alloy to generate as little hydrogen as possible during incidents while also matching the prior performance. To accomplish this, researchers designed the new alloy from scratch with a team of experts in nuclear engineering, materials science, radiation effects, corrosion, thermomechanics, and alloy fabrication. Bruce Pint, leader of ORNL’s corrosion science and technology group, was among the project’s key collaborators.
The alloy was identified and produced over six years, using tools, expertise, and testing equipment available at various DOE facilities. The alloy has now been turned over to industry for testing and evaluation, with the new cladding installed in February 2018 at a reactor in Southern Nuclear's Hatch Nuclear Power Plant near Baxley, Georgia, USA. Subsequent installations are planned.
“This was by no means an Edisonian approach,” Terrani said, alluding to the trial-and-error approach made famous by Thomas Edison. “We worked with knowledge and tools that were not [previously] available. We designed an alloy that we knew was going to work. I’m not surprised that this alloy behaves so well under different conditions; we designed it to do so.”
Source: ORNL, www.ornl.gov.