Managing Aging Nuclear Storage Canisters
Shannon Chu is a senior technical leader at the Electric Power Research Institute, where she manages multiple technical projects in the used fuel and high-level waste program. Her research has focused on developing aging management programs for welded stainless steel canisters used in independent spent fuel storage installations. Before joining EPRI, Chu trained with the Nuclear Regulatory Commission in the radiation protection and engineering branches.
In the process of producing nuclear-generated electricity, power plants obtain heat through fission, which is the splitting of atoms of uranium in a nuclear reactor. The uranium fuel consists of small hard ceramic pellets that are packaged into long vertical rods.
Nuclear plants were originally designed to provide temporary onsite storage of used nuclear fuel. About one-third of the fuel in a reactor is removed and replaced with fresh fuel during a refueling outage, which occurs every 18 to 24 months. This is done because the fuel rods lose efficiency over time.
Known as used fuel, these bundles of fuel rods generate considerable heat and radiation. After use, they are placed into deep pools of water at the reactor site, where they can be stored safely.
Reactor designers expected used fuel to be stored in pools for a few years before it was shipped offsite to be reprocessed at a plant. After arriving there it would be separated into portions that could be recycled into new fuel and the unusable portions that would be disposed of as waste. But commercial reprocessing never succeeded in the U.S., so pools began to fill up.
Utilities began turning to dry storage to manage their spent fuel onsite. After a few years in the pool, the fuel has cooled and its radioactivity has decreased enough to allow it to be removed. Moving spent fuel into dry canisters frees up space in the pool to store spent fuel newly removed from the reactor.