Resurrecting Three Mile Island
When Exelon Generation shut down Three Mile Island Unit 1 in September 2019, managers were so certain that the reactor would never run again that as soon as they could, they had workers drain the oil out of both the main transformer and a spare to eliminate the chance of leaks. The company was unable to find a buyer because of the transformers’ unusual design. “We couldn’t give them away,” said Trevor Orth, the plant manager. So they scrapped them.
Now they will pay $100 million for a replacement.
The turnaround at the reactor—now called the Crane Clean Energy Center—highlights two points: how smart Congress was to step in with help to prevent premature closures with the zero-emission nuclear power production credit of 0.3 cents per kilowatt-hour (only two years too late), and how expensive it is turning out to be to change course.
How we got here
The business decision to shutter TMI-1 seemed rational at the time. Natural gas was especially cheap, and the signal from the markets was that nuclear couldn’t compete, so reactor owners around the country ruthlessly pruned their holdings. Single-unit plants—even if they were running reliably, as TMI-1 was—were most vulnerable. In 2018, it was Oyster Creek; in 2019, it was Pilgrim along with TMI-1; and in 2020, Duane Arnold. These were all tough decisions, but boards answerable to shareholders or ratepayers did not see where the pattern of cheap gas, flat demand, and super-subsidized solar and wind was going to end.
So at Three Mile Island, workers promptly decommissioned the 30,000-gallon tank of safety-related diesel fuel in accordance with Pennsylvania rules, drilling holes in it and filling it with concrete. When the plant ran, it was essential to plant operation; when the plant didn’t run, it was a potential source of groundwater pollution.
They sealed the fuel transfer tubes, which connect the reactor to the spent fuel pool, with concrete, so that no intruder could get in. They drained the steam generators and opened them to air, usually considered a recipe for corrosion. They considered using the reactor vessel as a trash can for radioactive parts, but in the end they put the head back on and secured it with four hand-tightened bolts. They turned off the lights, the ventilation, and everything else in the containment building and prepared to walk away, with nothing but a skeleton staff remaining behind for the next few decades.
But a funny thing happened on the way to decommissioning. Exelon told the NRC in June 2017 that it would close the plant because of “severe economic challenges.” But a few years later, executives at Constellation Energy, which was created by the fissioning of Exelon in February 2022, looked at the multiple projections for an uptick in electricity demand and the willingness of highly profitable tech companies to pay a big premium for carbon-free electricity. They sat down to consider whether to invest in uprates at the company’s other reactors. They had some uprates underway and might squeeze another 40 megawatts out of other units, but the costs were substantial. Those uprates, however, were small compared with the more than 800 megawatts that could be gained from the lost reactor. “Suddenly,” said Constellation spokesperson Mark Rodgers, “what had seemed off the table, bringing TMI-1 back, started to look possible and even attractive.” That was true even at a price tag of $1.6 billion.
Inspections and surprises
The saga of Crane has quite a few surprises, and work on recommissioning is still just getting started. The long-lead-time item has turned out to be workforce—getting new control room personnel licensed for the site. “That’s dictating the timeline,” said Rodgers. Another potentially slow process is getting permission to reconnect to the grid operated by the PJM Interconnection, which is swamped with requests. But Pennsylvania Gov. Josh Shapiro and others have stepped in to try to get Constellation’s application closer to the top of the pile. That might require action by the Federal Energy Regulatory Commission—but PJM, foreseeing a capacity shortage, appears to want the reactor back on line, as well.
There are some technical surprises, too—mostly good ones. The cladding in the reactor coolant system was in good shape, with no sign of corrosion. The steam generators, replaced in 2009 with a newer model with heat-treated tubes, were found to be in good condition. The contractor who did the eddy current testing on the tubes managed the job despite coming into a building that had no electricity or air circulation. And technicians did not put a nitrogen blanket over the steam generator innards, which is the standard practice during a long shutdown when a re-start is planned. Managers at the plant decided that this was not a good option, because it would have required checking the integrity of numerous valves. The interim fix has been to connect dehumidifiers to the steam generators, keeping the relative humidity below 18 percent. (The Sahara Desert has an average relative humidity of 25 percent.)
Another happy surprise was the turbine. During a refueling outage, common practice is to rotate the turbine so it does not sag, but nobody bothered with this at Crane. A recent inspection found the turbine operable and the feedwater heaters, also left open to air, in good condition.
Inspections are continuing, and so far, Constellation has turned up no components or structures that have a lead time for replacement or repair that is long enough to push back the scheduled restart—currently set for 2028.
What about fuel?
The premature shutdown did result in some wasted fuel, however. Exelon retired the plant when it was time for its once-every-24-months refueling outage, when about one-third of the core is removed and replaced. Hence, one-third of the fuel had another two years of life left in it, and one-third had four years left.
TMI never had dry casks, but Constellation built 46 of them after the shutdown so it could empty the spent fuel pool of the fuel assemblies from 45 years of operation and drain it. In the process, the partially used fuel was spread among many casks, because decisions about how to load spent fuel casks are made with an eye to limiting the number of casks while optimizing thermal loading, mixing hot fuel with cooler fuel to stay within the temperature limit for each cask. Completing the defueling made sense at the time, since a potential restart wasn’t a consideration. Now, however, considering the cost of buying new fuel, Constellation did consider recovering some of the partially used fuel.
“Fuel’s not cheap,” observed Orth in a presentation last December to the Chicago–Great Lakes chapter of the American Nuclear Society. But recovering the fuel would have been a first-of-a-kind effort that entailed some small level of risk.
“The safest thing is not to even try,” said Rodgers. So the plant will start with fresh fuel, including a neutron source of the kind used only in first-time startups.
Workforce woes
When the site shut down, it had a workforce of about 650 people. Staffing was down to 80 people when the decision was made to restart, and it is slowly growing again. The first order of business is to train the instructors who will run the initial license training to develop a cadre of licensed operators. There are no licensed operators at the moment.
Constellation still employs former TMI workers at its other reactors, and some want to return. Others with nuclear experience—at Constellation sites or elsewhere—have also applied for jobs at Crane, said Rodgers. Constellation will allow staff to transfer from its other reactors to Crane if doing so does not hinder the operations of the other reactors, he said.
The company hasn’t laid out its costs in detail, but reconstituting a staff looks to be not only the slowest part but one of the most expensive.
And there is already an agenda for after startup. One item is to apply for license renewal. The current license expires in April 2034.
Matt Wald is an independent energy writer and consultant. He is a former policy analyst at the Nuclear Energy Institute and for decades was the energy reporter at the New York Times.
Correction notice: Mark Rodgers role as spokesperson for Constellation was corrected from the original article.
