The Department of Energy will tell you exactly how to drive to a buried nuclear reactor. Take I-80 west out of Lincoln, get off at the first exit, run south on US 77 for 20 miles, turn off toward the village of Hallam, then a mile north up a gravel road and a mile west. The power plant is visible from the gravel. Those directions sit on page 4 of a federal document dated January 2026, and the reactor at the end of them hasn’t moved since 1969. You don’t need permission to know any of this.
It’s still down there, it’s still radioactive, and the federal government pays to cut the grass on top of it.
So what’s under the grass?
The mound covers 1.4 acres, a little bigger than a football field with the end zones, and it’s flat on top with sloped sides so the rain runs off. Underneath you’ve got the below-grade half of the Hallam Nuclear Power Facility, and the reactor vessel is still sitting in a steel-lined cavity inside it. The Department of Energy’s Office of Legacy Management puts about 300,000 curies of radioactive material in there at the time of closure, and more than 99 percent of that is in the reactor cavity alone.
There’s no fuel down there. The uranium went to South Carolina in casks before anything got sealed, and what’s left is what the industry calls activation products. Your wrench doesn’t turn radioactive from touching uranium. Park it next to a running core for a couple of years and the neutrons do it for you, and that’s basically what happened to the vessel, the guard vessel, the thermal shield and the steel liner wrapped around all of it.
If you wanted in, DOE says you’d need explosives, air hammers and cutting tools.
The reactor only ran for 15 months
Hallam was rated at 240 megawatts thermal. That’s a heat number, not an electricity number. A reactor makes heat, the heat makes steam, the steam turns a generator, and you don’t get to keep most of it on the way through. Out the far end came 75 megawatts of electricity, and that went into the same turbine the coal boiler next door was already feeding.
Crews took the core critical in January 1962 and reached full power in July 1963. Then seven moderator elements ruptured in February 1964, the graphite soaked up sodium, the power in that part of the core dropped, and the reactor shut down that September. Atomics International wanted to fix it. The AEC ran the numbers, decided the repair wasn’t worth what it would buy, and terminated the operating agreement in August 1965.
Total output was 192,458,000 kilowatt-hours across 6,271 hours of running, which averages out to roughly 30 megawatts against a 75-megawatt nameplate. The AEC declared the program’s objectives fulfilled in June 1966 anyway, and by the standards of 1966 that’s fair enough. Hallam had shown a sodium-cooled reactor could push utility-grade steam into an ordinary turbine hall, and that isn’t nothing. The sodium reactors that came after it are the longer and sadder story.
Burying it was a three-year job
Nebraska Public Power District got the authorization in 1967 and finished in 1969. Roughly 550,000 pounds of primary sodium went out by rail to Hanford in Washington state for reuse, and another 220,000 pounds of secondary sodium went back to Atomics International. Crews drained the vessel down to a two-inch heel of sodium on the bottom, then pressurized it to 10 psig while pulling a vacuum on a drain tank until that heel was under a quarter inch. Whatever sodium was left got hit with steam on purpose, because sodium and water make hydrogen, and hydrogen in a sealed concrete box is the one thing you don’t want 50 years later. That reaction left 840 pounds of fused sodium hydroxide sitting in the vessel and its lines, and the American Nuclear Society went back through its own 1970 reporting to pull that number out.
Then came the sealing. Welded steel closures over the cavities, reinforced expanding concrete in the stairwells and pipeways, a layer of sand, a polyvinyl membrane and soil over the concrete ceiling, drain tile around the edge, and a coat of concrete over the one building still standing above ground.
The paperwork got the strangest treatment of all. Drawings of the layout, the vessel location and the engineering details were sealed into two stainless steel capsules measuring 24 by 19 by 4 inches. One went into a niche cut in the south face of the heat exchanger structure, under an engraved plaque that tells whoever reads it what’s inside. The other one’s buried under the cover at the reactor centerline. It’s arguably the most literal time capsule the American nuclear program ever produced, and it exists because somebody in 1969 assumed the people who open this thing won’t have met anyone who built it.
The Energy Department mows the lawn
Legacy Management inspects the site once a year and looks at five things: the heat exchanger building for cracks, the mound for erosion on the side slopes, the wells for damage, the boundary monuments, and whether the sprinkler system is ready for the season. DOE owns that sprinkler system. DOE mows too, plus fertilizer and weed control, because if the turf dies you’re washing the cover off the concrete underneath. You’re paying for a lawn service on top of a reactor, and it’s a fairly reasonable thing to spend the money on.
The wells are where the monitoring actually happens. Nineteen of them sit in eight clusters around the structure, screened at about 25, 50 and 75 feet, and 17 get sampled for gross alpha, gross beta, nickel-63, tritium, gamma emitters and total uranium. Two only give water levels, because they don’t refill fast enough to sample. Sampling ran every year until 2007, then every two years, and since 2016 it runs once every five. So what have five decades of samples turned up? Nothing above background, going back to 1970. One sampling event is due this year under that schedule, and I can’t find results from it posted yet.
Here’s where DOE disagrees with DOE. The site’s Long-Term Surveillance Plan puts unrestricted release at 2071, exactly 100 years after the AEC’s termination order of July 20, 1971, while the public fact sheet says around 2070. Either way you’re looking at another century of mowing, and the same plan works out that the nickel-63 down there won’t decay to the level the Department of Transportation calls exempt for shipping until the year 4189. Compare that with the Finnish repository at Onkalo, which is being built to need zero human attention from the day it’s sealed.
One more thing about that field. The AEC’s 1971 safety evaluation worked through tornado wind loading and tornado-borne missiles and concluded that neither could reach the structure, since the whole thing sits at or below grade with sand and earth over the top. On May 22, 2004, an F4 tornado two and a half miles wide, the widest ever measured at that point, tore 52 miles across southeast Nebraska and went through Hallam, tipping hopper cars off a freight train on the west side of town. That’s out of the National Weather Service damage survey. I haven’t found an inspection report that mentions the mound in connection with that storm.
Nebraska Public Power District still runs Sheldon Station on Powder River Basin coal, 225 megawatts, hauled in by Union Pacific on rail spurs the utility owns. The reactor sits under 1.4 acres of the same property, sealed, mowed and watered. The surveillance plan covering it is dated January 2026, and the map bound into that plan is labeled 2025 Inspection Drawing.
