Assistant professor of nuclear science and engineering Michael Short and collaborators — professors Bilge Yildiz, Matteo Bucci, and Evelyn Wang, as well as the MIT Nuclear Reactor Laboratory and the Westinghouse Electric Company — have received $4.5 million in funding from Exelon to support research that could transform the performance of fuel rod outer layers, known as cladding, in light water reactors (LWRs).
Four major problems negatively affect the safe and reliable operation of LWR fuel cladding: fretting and wear from grid-to-rod-fretting (GTRF) and foreign material; the buildup of porous corrosion deposits known as “crud”; hydrogen absorption; and boiling crisis. Fretting can wear through the fuel cladding, while crud and hydrogen absorption can lead to corrosion-based fuel failure, respectively. Finally, a “boiling crisis” is when the normally bubbly mode of coolant boiling, called sub-cooled nucleate boiling, transitions to film boiling, insulating the fuel with a layer of steam and worsening heat transfer. All four can and have caused failure of the fuel cladding, leading to radioactive releases into the coolant and costing reactor operators over $1 million per day of downtime to fix the problem.
The goal of the newly funded MIT project is to address all four issues at once by developing a viable solution within three years, consisting of engineered cladding surface coatings and micro/nano-geometric modifications. The team will design a set of coatings and surface modifications for Zircolay-based fuel cladding currently in use. The combination will simultaneously:
- minimize or prevent crud (chalk river unidentified deposits) buildup and hydrogen pickup, which in turn will increase the lifetime, stability, and power density of the fuel;
- improve hardness to prevent grid-to-rod fretting, which occurs when the spacer grid (a metal piece which separates the fuel rods) and the rods themselves vibrate and wear holes into the metal; and