When running an AI model at a single site requires you to provide electricity to power and cool 100,000 accelerators, or maybe even a million of them in a few years, you have to start thinking about the unthinkable if you also want to use carbon-free juice to power your AI ambitions.
That’s why we find Microsoft’s 20-year contract with Constellation Energy to upgrade and restart one of the decommissioned nuclear reactors at the ill-fated Three Mile Island Unit Nuclear Power Plant on the Susquehanna River south of Harrisburg, Pennsylvania, not only ironic but prophetic. You have to be very dependent on electricity to be willing to go anywhere near Three Mile Island to get it.
Like many of you reading this, I remember the partial meltdown in TMI’s reactor unit 2 that occurred on March 28, 1979, and I also remember the movie The China Syndromewhich came out twelve days before the accident and shortly after my 14th birthday. I have always been fascinated by nuclear fission and fusion reactors, and I remember very clearly writing a book report – like my wife Nicole, I wrote book reports on my own, just because I felt like it, not because teachers told me to – about a containment vessel breach and a meltdown in the 6th century.th class with my new crayons from Christmas. It was a 3D cutaway view, as far as I remember. (I can’t find the magazine, but I think it was an article in Popular mechanicsthat I read in the school library and that plunged me into this rabbit hole of breakdown.) I was not prophetic, but The China Syndrome that was definitely it.
The interesting thing for me was that I decided to be a writer, not an engineer, when the Space Shuttle Challenger exploded on launch in January 1986—I was in my third year of aerospace engineering and had just dropped out of electrical engineering mid-semester. By that time, I had already been working as a writer for Penn State’s nuclear engineering department to pay my tuition. Ed Klevans, who had worked at Penn State for nearly four decades, first as associate dean for research and then as professor and head of the NucE department, gave me my first writing job—and I want to thank him for setting me on my path and for being a good and kind editor.
The funny thing is, while I was there working on the department’s monthly newsletter, I learned all sorts of interesting things about the field and even got to tour the small water-moderated fission reactor on campus. And because I love irony, I also learned a lot about the company behind Three Mile Island, which was, no joke, called GPU Incorporated, and which we all called GPU Nuclear. (That’s short for General Public Utilities.) As you can imagine, a lot of the NucE department back then was working with GPU Nuclear to figure out what was going on inside the TMI-2 containment vessel and the best way to clean it up.
Through a series of mergers and spin-offs, the working TMI-1 rector ended up in the hands of Constellation Energy, which merged with Exelon and then spun off from Exelon, retaining control of the TMI-1 unit. (The TMI-2 unit was gutted and is still owned by a company called Energy Solutions, which was formed after the meltdown to manage it.) TMI-1 was offline for six years, but was brought back online in 1985. Before the Constellation Energy spin-off, Exelon threatened to shut down TMI-1 in 2015—presumably because it wasn’t making money from it—and four years later TMI-1 was shut down.
As part of the deal with Microsoft, Constellation will invest $1.6 billion to bring the TMI-1 pressurized water reactor back online by 2028. It will generate around 835 megawatts of electricity. The electricity generation capacity of power plants is usually measured by the number of homes they can supply with electricity. Depending on who you ask, that number is between 700,000 and 800,000 homes.
We propose a different metric. If the average GPU in 2028 runs at 1,500 watts – and there’s no reason to assume GPUs won’t be that hot in three to four years – then that’s about 560,000 GPUs. Assuming the goal is to get to 1 million GPUs by that time – which is the case according to the founding premise of the Ultra Ethernet Consortium – then that’s just a little over half of that future AI cluster.
Looks like Microsoft Energy Solutions will help launch and upgrade TMI-2. . . .
Neither Microsoft nor Constellation have said what Microsoft will pay for the power from the plant.
In 2019, when it was decommissioned, TMI-1 produced electricity 96.3 percent of the time at a maximum capacity of 837 megawatts in its last full year of operation. The plant had 600 full-time employees with an annual payroll of $60 million. Another 1,000 employees (mostly union members) were involved in the biennial nuclear fuel refill operations. (We don’t know how long these last, but during that time, the power Microsoft needs for its AI data centers clearly has to come from somewhere else.)
Incidentally, Constellation is the largest nuclear power plant operator in the USA with 21 reactors at 14 locations.
The TMI-1 reactor began generating electricity in 1974, and the TMI-2 reactor (which partially melted because a loss of coolant prevented neutron moderation) operated for only six months before taking itself offline thanks to the LOCA. The $1.6 billion covers the cost of installing a new transformer and upgrading the turbines and generators used to generate electricity, as well as upgrading the cooling system for the reactor. The combination of the nuclear plants, wind farms, and solar farms generates enough electricity to power around 16 million homes, and therefore about 11 million future GPUs. (Well, if those 16 million people agree to shut off their electricity, it might be possible.)
And although no one will ever use that term, Constellation is renaming Three Mile Island the Crane Clean Energy Center, after Chris Crane, former Exelon CEO and big fan of nuclear energy.
As already reported by our sister publication, The RegisterAmazon Web Services has a $650 million deal with Talen Energy for a 960-megawatt data center next to its nuclear power plant on the upper Susquehanna River southwest of Scranton and northwest of Harrisburg. We always drove past this plant when we visited family in western Pennsylvania, and it looms pretty large on the Alleghany Plateau.
It’s funny to think that these massive nuclear reactors aren’t enough to power future AI clusters, and that we’ve dismantled so many reactors that can’t be easily or cost-effectively restarted.
We need nuclear fusion as an energy source, like yesterday.
