High Flux Isotope Reactor team keeps neutron source running day, night

At 85 megawatts, ORNL’s High Flux Isotope Reactor is the strongest reactor-based neutron source in the nation, and one of very few such research reactors in the world. More than 500 scientists a year come from all around the globe to ORNL to use HFIR to study physics, chemistry, materials science, engineering and biology.

HFIR runs in cycles; sometimes it’s operating, and sometimes it’s quiet. Either way, day or night, there are always people there.

Many nights, Joe Galloway is one of them. A radiological control technician, Galloway monitors the HFIR building for radiological conditions, ensures safety protocols are followed, and supports Operations with activities that involve radiological material. When he works a day shift, he’s one of multiple RCTs. But when he’s working night shift, he’s the sole responder.

“It’s a little more responsibility,” Galloway said.

HFIR can draw a crowd during daytime hours when it’s running. There are operators for the reactor and its cold source cryogenic plant, researchers performing experiments, ORNL staff using the reactor to irradiate targets to produce in-demand isotopes, and a bevy of electricians, pipefitters, millwrights and other craft resources. Add to that the occasional tour coming through, and it stays pretty busy.

“You could come in and be doing one job, and you turn around and get a phone call to go cover another,” Galloway said. “It’s a faster pace.”

It stays busy even at night when HFIR is running. Time slots to use the reactor and its instruments are so coveted, researchers take what’s available. It may be noon on a Wednesday; it may be 2 a.m. on a Friday.

HFIR uses a beryllium reflector and is cooled and moderated by light water and fueled by elements containing uranium-235. Its core has three regions of components surrounding an area of very high thermal-neutron flux, which captures thermalized neutrons within the reactor’s flux trap, allowing it to produce isotopes. Operators can use hollow “beam” tubes to move neutrons from the reflector into experiments outside the reactor’s shielding, and materials can be placed in holes in the reflector to be irradiated for one or more cycles. But there’s limited space for targets, and some of those spaces are reserved for ORNL’s production of isotopes for medicine, energy, industry and research.

“For us, nights and days aren’t a whole lot different,” he said. “I run the reactor so the scientists can do cool stuff. The things the researchers do here are just fascinating.”

When HFIR is between cycles, the building is emptier at night. There’s an RCT – in this case, Galloway – and a supervisor, like Flory, and three operators. As a small team, they work closely and intuitively. 

“They know my expectations,” Galloway said. “I know their expectations and what they need from me. It’s a lot less stressful.”

These non-cycle nights are filled with what usually are routine tasks: checking systems and instruments, looking for leaks, and performing administrative duties. 

“If something comes up, we deal with it,” Flory said.

Like many other ORNL workers, Galloway, Flory and their team work a rotating schedule where they flip between nights and days. For Tiara Culp, who became an operator just last year, it’s her first night-shift job. Culp, also a Navy veteran, previously worked on an aircraft carrier nuclear plant in the Navy. The satisfaction of working at a world-renowned research reactor, she said, makes adjusting to a new shift worth it.

“The work is pretty engaging, even when you’re tired,” said Culp, who invested in a sleeping mask, blackout curtains and a white noise machine for daytime sleeping. “Here, it’s all research and learning and experimentation. Your priorities are different. Your goals are different.”

Flory was present for HFIR’s 500th cycle, in December 2022. The reactor began operation in 1965, primarily to produce “heavy” elements like plutonium and californium, though its mission has vastly expanded since.

“That was a big day,” he said.