A few weeks ago, I bemoaned the fact that my tour of a nuclear generating station didn’t include a peek at the inner workings of the plant. I relayed the same rant over dinner with friends, who tipped me off to something exciting: there is a reactor in my city that I can go visit.

Here in Hamilton, McMaster University has a 5-megawatt open pool reactor nestled in the middle of the verdant campus. They offer tours to school groups, researchers, and nosy nerds; obviously, I signed up (a virtual tour is available here). Our group was hosted by an enthusiastic graduate student who led us through an airlock into the heart of the university’s nuclear program.

Since my interest in nuclear technologies was focused on their role in energy systems, I was surprised to learn that this reactor is not used to generate electricity; its job, instead, is to irradiate materials for research and radioisotope production. In a nuclear power plant, the primary product of the fission reaction is heat, which is used to generate steam, which turns a turbine. But the McMaster reactor’s primary purpose is to research the more fantastical aspects of fission, and the heat from the fission reaction is simply dissipated at nearby cooling towers. As our guide explained, the only beneficiaries are the raccoons who huddle up to the towers for warmth. The tour walked me through the inner workings of the reactor and underscored the fact that the energy released during fission is just one part of the reaction; a nuclear reactor is also an alchemical crucible, transforming matter at the subatomic level.

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The nuclear reactor I toured last month – and, by extension, any power-generating nuclear reactor – is basically a steam engine bolted on top of one of the wildest and most counterintuitive reactions humans can control. Fission is fundamentally unlike combustion or any other chemical reaction in that it breaks atoms – long thought to be the immutable building blocks of matter – apart, creating entirely new kinds of matter. Inside nuclear reactors and cyclotrons, scientists transmute and transform elements, carefully tailoring decay chains or positioning stable elements to create radioisotopes. To call someone an alchemist is to imply they’re a charlatan; most self-proclaimed alchemists are not, in fact, able to turn lead into gold. But nuclear scientists are not selling snake oil. The alchemy of nuclear reactors is effective.

The first reactors grew out of a desire to produce plutonium-239 for the Manhattan Project’s bombs. Plutonium only occurs in trace amounts on Earth, and in the 1940s the element had never been observed. However, there were blank spaces on the periodic table which predicted the existence of more elements. In 1941, scientists at Berkeley were trying to fill in some blanks, namely elements 93 and 94. They bombarded uranium-238 with neutrons, forming uranium-239. In a short time, this isotope decayed to a new element, number 93, soon dubbed neptunium. After a few days the material decayed again, forming the first observable quantity of element 94; keeping with the planetary theme, it was named plutonium. With a half-life of 24,100 years, the sample of plutonium-239 remained available for study and its fissile nature was determined. The discovery became a state secret, and the state wanted more of the material.

The first nuclear reactor was built in 1942, aiming to reproduce this same decay chain, which transmutes uranium into plutonium. Reactor fuel is largely made up of uranium-238, with an additional 3-5% uranium-235 – the former being the fissionable isotope. When a uranium-235 atom is struck by a neutron, it splits into two, and the resulting components themselves are transmuted into different chemical elements. It also emits an immense amount of energy and an additional neutron. When these neutrons collide with another uranium-235 atom it maintains the reaction: More atoms are split, and more neutrons are emitted. When these neutrons collide with uranium-238 atoms, they begin the transformation into plutonium-239. Because its half-life is so long, plutonium-239 accumulates in the reactor and can be separated from the rest of the fuel.

The Oak Ridge X-10 Graphite Reactor face, the first production reactor built as part of the Manhattan Project. It acted as a proof of concept for scaling plutonium production. Image via Wikimedia.

The technique was scaled up with the construction of reactors at Oak Ridge, Tennessee, and Hanford, Washington. Here, as nuclear chemist James C. Warf explains, “milligrams of plutonium, then grams, and finally kilograms, were produced.” Just 6.2 kilograms of plutonium made up the core of the bomb dropped on Nagasaki. In the span of four years, a new element had been discovered in trace amounts and then created at scale in the roiling crucible that is a fission reactor. Frankly, I find it horrifying that humans discovered a fundamentally new way of manipulating matter – we discovered new elements in a lab! – and immediately applied the knowledge to violence and destruction.

While I doubt I will ever learn to stop worrying and love the bomb, my visit to McMaster’s reactor illuminated the peaceful applications of nuclear transmutation. Here, the staff produces radioisotopes for medical imaging and cancer treatment. The university is the world’s leading provider of iodine-125, used to treat prostate cancer, and holmium-166, used to treat liver cancer. These isotopes are sold to hospitals, funding the nuclear science and engineering programs and supporting the reactor’s operating costs.

McMaster’s open pool reactor looks quite a bit like a tiled swimming pool if you ignore the pipes, instrumentation, and eerie blue glow. Technicians use long poles to lower stable elements through the 10 meters of water and into the reactor core. When non-radioactive material is inserted into the reactor core and bombarded with neutrons, radioisotopes are created. To produce iodine-125, a canister of xenon gas is bombarded with neutrons, resulting in a plethora of radioactive isotopes of xenon. One of these isotopes, xenon-125, decays to iodine-125, which can be life-saving for prostate cancer patients. Brachytherapy, derived from the isotope, has a consistently high disease-free survival rate: “Approximately 95% for low risk, 91% for intermediate risk and 82% for high risk.”

While the production of radioisotopes is akin to alchemy, once the isotopes are harvested and refined, familiar shipping and logistics challenges emerge (with a few layers of added complexity). For one thing, radioisotopes are dangerous goods so stringent guidelines must be followed. Further, radioisotopes decay and therefore cannot be stockpiled; short-lived medical isotopes must be shipped by air immediately to client healthcare providers. Iodine-125 has a half-life of 60 days, while holmium-166 has a half-life of 26.8 hours. An isotope used in medical imaging, technetium-99m, has a half-life of just 6 hours. Since it would be functionally impossible to ship it anywhere, its parent isotope, molybdenum-99 (half-life of 66 hours), is shipped to hospitals and decays to technetium-99m on site. As with other time-sensitive cargo like sushi-grade tuna, radioisotopes are generally transported in passenger aircraft as they run frequently and are usually on time. In 2021, when COVID-19 meant most passenger flights were canceled, transporting radioisotopes was particularly difficult and some shipments decayed past their useful lifespan while waiting in airports.

Time isn’t the only supply chain risk for medical isotopes. This report on technetium-99m and molybdenum-99 production found that most facilities that produce radioisotopes are aging and need to be taken offline to undergo extended maintenance. Several reactor shutdowns in 2022 caused shortages of the isotope pair, and some Canadian hospitals had to cancel 90% of their associated testing. And the peaceful atom isn’t immune to the machinery of war: Rosatom, Russia’s state nuclear company, is the sole commercial supplier for some medical isotopes. Despite the fact that the company occupies the Ukrainian Zaporizhzhia nuclear power station, Rosatom has largely avoided sanctions since many nations rely on it for isotopes and nuclear fuel. To date, only Rosatom subsidiaries have been sanctioned, in hopes of keeping some trade flowing (much to the frustration of Ukrainian officials). Even if further sanctions don’t materialize, that trade could be disrupted if Russia decides to block exports. The US is building out its capacity to produce the isotopes that Rosatom currently supplies, but it will take until 2032 for the new facility to come online.

I wanted to visit a nuclear reactor to understand the benefits and drawbacks of our nuclear energy systems. While the energy density of uranium is astonishing – in a reactor, one kilogram of unenriched uranium yields about 20,000 times more energy than burning a kilogram of coal – but dealing with long-lived waste products, like plutonium-239, is an ongoing challenge. Not only do caches of weapons-grade material build up at reactor sites, but humanity has tasked ourselves with safely managing material with a half-life of over 24,000 years – while recorded human history is only 5,000 years! Counterintuitively, visiting a nuclear reactor that doesn’t produce electricity has given me insight into how this waste problem was created in the first place. The first reactor was built in 1942, shrouded in the secrecy of the Manhattan Project, and the reactors at Oak Ridge and Hanford were designed to maximize plutonium-239 output for weapons production. It wasn’t until 1951 that the first nuclear reactor produced electricity. I’m still ambivalent about nuclear energy, but this trip helped me realize just how much more interesting and complex nuclear science and technology is. The inside of a reactor is bizarre and beautiful, a boisterous world of alchemical transformation that can be applied toward preserving and honoring life.


Thanks as always to Scope of Work’s Members and Supporters for making this newsletter possible. Thanks to Paul for telling me McMaster has a reactor, to Edcer Laguda for hosting our tour, and to Dave and Daemon for joining. A big thanks and apology to Sam, Lars, Eric, and Heather whom I brought out to the reactor on the wrong day – at least our lunch was really delicious! Thanks also to Carl, Stu, and David for their fact checking efforts; any remaining mistakes are my own.

This issue relied heavily on James C. Warf’s All Things Nuclear, a pleasantly readable overview of, well, all things nuclear. The latest version was published in 2005, so some information is dated (he reports that lithium batteries will someday make their way into EVs) but for getting a handle on the core concepts, it’s a great resource. I also found this short lecture on radioisotope production very helpful (the section about neutron bombardment in a reactor starts here).

Love, Hillary

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