The High Flux Isotope Reactor, a key research facility at Oak Ridge National Laboratory, has the lowest fuel inventory in its history. And that’s saying something for a nuclear reactor that’s been in business since the mid-1960s.
After the ORNL reactor is refueled for scheduled start-up on Jan. 13 (it’s currently shut down for maintenance), there will be only six fuel assemblies available for future use. That’s not much considering the fuel cycle for HFIR is only 23 days, which means it has to be refueled about once a month.
Mind you, the HFIR doesn’t use just any old, off-the-shelf nuclear fuel. The hundreds of intricate and complex fuel plates that comprise the reactor’s nuclear core — and provide remarkably concentrated streams of neutrons for material experiments and production of radioisotopes — are made with highly enriched uranium. That’s very, very enriched uranium, consisting of 93.8 percent U-235, the fissionable isotope of uranium. Because the uranium is bomb grade, special approvals are involved with lots of security.
The back-up fuel elements for HFIR are stored at the Y-12 nuclear weapons plant, about 10 miles from the lab, until it’s time for reloading. The fuel core at the reactor contains 9.4 kilograms of U-235.
The inventory of uranium fuel for the High Flux Isotope Reactor was allowed to dwindle over the years, apparently to save money for other uses or to make do during tight budget times.
“It’s been a budget issue,” said Ron Crone, an associate lab director.
ORNL hopes to operate the reactor for decades to come, and plans are underway to try to rebuild the reactor’s fuel supply.
Depending on how funding works out for the rest of Fiscal Year 2015, ORNL expects to receive 6 to 8 additional fuel elements in coming months, according to Tim Powers, the lab’s reactors chief.
“So, at the beginning of the next fiscal year (Oct. 1), the inventory will either be the same or more than the previous year,” Powers said via email.
If that happens, it would be the first time in “many years,” he said, and “a step in the right direction.”
Each fuel load for the ORNL reactor costs a little more than $1.5 million, but that’s sort of a bargain because the lab doesn’t have to pay for the highly enriched uranium obtained from Y-12 — the nation’s principal repository for weapons-grade material.
ORNL’s costs are for the processing of the uranium, initially at Y-12 — where it made into a uranium oxide powder — and later at the Babcock & Wilcox facility in Lynchburg, Va., where the powder is pressed (reportedly using 38,000 psi of force), rolled, stamped, and fabricated into high-quality uranium elements with aluminum cladding.
“HFIR has run over a quarter-million plates, and we’ve never once had a leaking fuel element,” Crone said.
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