Nuclear Diving: Spent Fuel Pools and FME Controls
By Walt Kesler, Power plant maintenance manager, nuclear-qualified. Reviewed by Amanda McCallister, editor.
Underwater Inspection | Commercial Diving Contractors Alabama I remember a dive we did in the spent fuel pool during our last refueling outage. We had a piece of wire mesh, maybe a two-inch square, sitting on the floor between the fuel racks. The dose rate at the surface was nothing to worry about, but the FME bookkeeping was a beast. That's what this job is about: keeping every single item accounted for, even with a guy in the water. I'm Walt. I've been a maintenance manager at a nuclear plant for over twenty years, and I've overseen dozens of these dives. The work isn't glamorous, but it keeps the pool clean and the fuel racks free of debris. If you're ever called on to plan or supervise a spent fuel pool dive, here's how it works.
What You're Actually Doing Down There
We're not Hollywood divers. We're mostly doing inspections and light maintenance. The typical job is a visual sweep of the pool floor and the fuel racks, looking for any small items that could have been dropped during fuel movement. Sometimes we'll use a diver-held underwater video camera, like a DeepSea Power & Light SeaCam, and pan across the racks. Other times we'll vacuum up small debris using a suction probe, often called a slurp, with a catch basket. The depth is around 40 feet, call it 40, give or take. The water does an incredible job of shielding radiation, so the diver isn't exposed to anything like the core. But the fuel is right there, yards away. You don't touch it. Ever. And you don't leave anything behind. I've also been on jobs where we need to install or remove underwater brackets or bumpers that protect the racks from dropped loads. Those are the risky ones because you're carrying hardware in a bag or on your person. That's where FME controls really go into overdrive.
The FME Rules Are Absolute
Foreign material exclusion — FME — is the whole ballgame. Anything left in the pool can interfere with fuel handling, block cooling flow, or damage fuel assemblies. So we run FME like the military runs a loading dock: every piece of equipment is inventoried, tied off, and double counted before and after the dive. The setup starts in the staging area. Every tool, every clamp, every screw is logged in an FME log. Each tool has a lanyard and a colored tag. The dive supervisor and the plant FME coordinator personally inspect the diver's suit for loose zippers, bad seals, or stray threads. We even have a designated retrieval kit — a magnetic wand, a net, a grabber — staged at the poolside, just in case something goes in. During the dive, the camera feed is watched continuously. If anything drops, the dive is halted and the item is found before the diver can move on. We call it "can't proceed until it's accounted for." No exceptions. The FME log is closed out after the diver is out and all items are counted a third time.
The Dive Setup and a Digression
We use surface-supplied diving, not scuba. A Kirby Morgan 37 helmet, a full-face mask with comms, and an umbilical that carries air, comms, video, and a safety cable. The air comes from a cascade system or a compressor with a backup. The divers are in a dry suit or a wetsuit depending on the pool temperature — usually around 75°F. But it's not a tourist experience. One time, we had a new diver come up with a missing clip on his harness. The dive supervisor spotted it on the camera as it fell. We stopped the dive, and the diver had to go back down with a magnet to pick it up. He was embarrassed, but everyone was relieved he didn't try to fish it out without the magnet. That's the kind of thing you learn early: FME is unforgiving, and a little humility goes a long way. We also do a practice run with "dummy" items to make sure the diver can handle the retrieval tools. It's a different feel underwater with thick gloves and a helmet on, so we always simulate before the real thing.
What It Takes to Be a Nuclear Diver
The guys and gals who do this work are commercial divers first. They've got certification through an accredited school like Commercial Diving Academy or Santa Barbara City College. But that's just the start. They also need radiological training from the plant, including a briefing on ALARA and emergency procedures. And they have to pass a plant-specific FME qualification, which covers the exact rules we use during outages. A typical dive might last anywhere from 20 minutes to an hour, depending on the work scope. The dive team is almost always a crew of three: a diver, a standby diver, and a dive supervisor. At a minimum, the supervisor is in constant voice and video contact. The diver wears a dosimeter, and we track dose, but the numbers are usually tiny — well below any reporting threshold. That's the beauty of water shielding. You might think you need to be a nuclear engineer to pull this off. You don't. But you do need to respect the environment and understand why the rules exist. The fuel stays safe because we keep the pool clean and the hardware intact. That's the actual job.
Frequently Asked Questions
Can you actually dive in a spent fuel pool? Yes, it's done routinely during refueling outages. The water provides excellent shielding, so the dose rates are very low. But it's a highly controlled operation with strict FME rules. What is FME? Foreign material exclusion. It's a set of procedures to prevent any foreign object from being left in plant systems. In the pool, even a small piece of metal can interfere with fuel handling or block cooling, so everything is counted and controlled. How deep is a spent fuel pool? Depends on the plant, but typically about 40 feet, give or take. The fuel racks sit on the bottom, and the water above provides radiation shielding. Do divers ever touch the fuel? No. Diving work is always done in areas adjacent to the fuel racks, but the diver never comes into physical contact with fuel assemblies. The work is planned to keep clearances.