AI Powerhouses Choose The Nuclear Option

When you need to provide electricity to power and cool 100,000 accelerators, or maybe even 1 million of them in a few years, in a single location to run an AI model, you have to start thinking about the unthinkable if you also want to use carbon-free juice to power your AI ambitions.

Which is why we think that Microsoft’s 20-year deal with Constellation Energy to retrofit and fire up one of the mothballed nuclear reactors at the ill-fated Three Mile Island Unit nuclear power plants on the Susquehanna River south of Harrisburg, Pennsylvania is not only ironic, but prophetic. You have to need electricity pretty bad if you are willing to go anywhere near Three Mile Island to get it.

Like many of you reading this, I remember the partial meltdown of the TMI Unit 2 reactor that happened on March 28, 1979, and I also remember the movie The China Syndrome, which came out a dozen days before the accident and right after I turned 14. I have always been fascinated by nuclear fission and nuclear fusion reactors, and I remember very clearly writing a book report – like my wife Nicole, I did book reports on my own just because I felt like it, not because teachers assigned them – about a containment vessel breach and meltdown in the 6^th grade using my new color pencils from Christmas. It was a 3D cutaway view, I remember.  (I can’t find the magazine, but I believe it was an article in Popular Mechanics, which I read in the school library, that sent me down that meltdown rabbit hole.) I wasn’t prophetic, but The China Syndrome sure as hell was.

The interesting bit for me was that when the space shuttle Challenger blew up during takeoff in January 1986 when I was in my third year of studying aerospace engineering and walking out of an electrical engineering mid-term, I decided to be a writer and not an engineer. At the time, I had already been working as a writer for the nuclear engineering department at Penn State to help pay for my tuition. Ed Klevans, who worked at Penn State for nearly four decades, first as an associate dean for research and then as a professor and the head of the NucE department, gave me my first writing job – and this is a shout out to him for setting me on my path and for being a good and kind editor.

Here’s the funny bit. While I was there working on the monthly departmental newsletter, I learned all kinds of neat things about this field, and I even got to tour the baby water-moderated nuclear fission reactor on campus. And because I love irony, I learned a lot about the company behind Three Mile Island, which, I kid you not, was called GPU Incorporated and what we all called GPU Nuclear. (It is short for General Public Utilities.) As you might imagine, a lot of the stuff going on in the NucE department at the time was working with GPU Nuclear to figure out what was going on inside of the TMI-2 containment vessel and figuring out the best way to clean it up.

Through a whole series of mergers and spinoffs, the working TMI-1 rector ended up in the hands of Constellation Energy, which merged with and then separated from Exelon and which kept control of the TMI-1 unit. (The TMI-2 unit had its core removed and is still owned by a company called Energy Solutions, created to manage it after the partial meltdown.) TMI-1 was offline for six years but was spun back up in 1985. Before spinning out Constellation Energy, Exelon started threatening to shut down TMI-1 in 2015 – presumably because it was not making money on it – and four years later TMI-1 was mothballed.

Under the deal with Microsoft, Constellation will invest $1.6 billion to bring TMI-1 pressurized water reactor back online by 2028, and it will generate around 835 megawatts of electricity. People commonly gauge the generating capabilities of power plants by the number of homes that can be juiced by them, and depending on who you ask this is somewhere between 700,000 and 800,000 homes.

We propose a different measure. If the average GPU in 2028 is running at 1,500 watts – and there is no reason to believe that GPUs will not be that hot three to four years from now – then that is about 560,000 GPUs. Assuming the goal is to reach 1 million GPUs by about that time – which it is according to the Ultra Ethernet Consortium’s founding premise – then this is just a little more than half of that future AI cluster.

Looks like Microsoft will be helping Energy Solutions fire up and retrofit TMI-2. . . .

Neither Microsoft nor Constellation have said what Microsoft is going to be paying for electricity out of the plant.

In 2019, when it was mothballed, TMI-1 was producing power at maximum capacity of 837 megawatts 96.3 percent of the time during its last full year of operation. The plant had 600 full-time employees with an annual payroll of $60 million. There were another 1,000 employees (mostly in unions) nuclear refueling operations, which happen every two years. (We do not know how long these take, but clearly during that time the electricity Microsoft needs for its AI datacenters will have to come from somewhere else.)

By the way, Constellation is the largest operator of nuclear power plants in the United States, with 21 reactors on 14 sites.

The TMI-1 reactor started producing power in 1974, and TMI-2 reactor (the one that melted partially from a loss of coolant accident that prevented the moderation of neutrons) was only operating for six months before it took itself offline thanks to the LOCA. The $1.6 billion covers the cost of putting in a new transformer and upgrading the turbines and generators used to make electricity and upgrading the coolant system for the reactor. The combination of its nuclear plants, wind farms, and solar farms produces enough electricity to power around 16 million homes and therefore about 11 million future GPUs. (Well, if those 16 million people agree to turn of their power it could.)

And, although no one will ever use this term, Constellation is renaming the Three Mile Island to the Crane Clean Energy Center, after the Chris Crane, the former chief executive officer of Exelon and a big believer in nuclear power.

As was previously reported by our sister publication, The Register, Amazon Web Services has inked a $650 million deal with Talen Energy for a 960 megawatt datacenter site adjacent to its nuclear power station on the upper Susquehanna River southwest of Scranton and northwest of Harrisburg. We used to drive by this plant on the way to visit family in western Pennsylvania, and it looms pretty large on the Alleghany Plateau.

It is funny to think that these massive nuclear reactors are not enough to power future AI clusters. And that we have dismantled so many reactors that can’t easily or cost-effectively be brought back online.

We need nuclear fusion power generation, like yesterday.