What happens to SMR waste? A simple guide
Small modular reactors promise a cleaner grid, but the leftover fuel still has to go somewhere, and right now that somewhere is a parking lot next to the reactor
Nuclear power has an image problem, and it is not really about meltdowns anymore. Ask most people what worries them about a reactor in their backyard, and the answer usually circles back to one word: waste. ☢️ Small modular reactors get pitched as the fix for almost everything wrong with nuclear power, cheaper, faster to build, safer by design. What gets talked about far less is what comes out the other end. So let’s actually walk through it: what SMR waste is, how much of it there is, where it sits today, and why the honest answer to “where does it go” is still, mostly, nowhere permanent. 🔬
Not all nuclear waste is the same thing
The word “waste” hides a lot of variety, and that matters because each type gets handled completely differently. Regulators sort it into three broad buckets, and understanding them clears up most of the confusion people have about nuclear cleanup. 🧬
Low-level waste: contaminated gloves, tools, filters, and protective gear. Decays fast and typically goes to a near-surface disposal facility
Intermediate-level waste: reactor components and resins with higher radioactivity that usually need some shielding but not deep burial
High-level waste: the spent fuel itself, along with reprocessing byproducts, and this is the stuff that actually keeps regulators up at night
<cite index=”50-1”>Most low-level waste is typically sent to land-based disposal facilities relatively soon after packaging</cite>, and that part of the system genuinely works. The trouble starts with high-level waste, the spent fuel rods pulled straight out of the reactor core, still hot, still radioactive, and still dangerous for a very long time. That fuel <cite index=”48-1”>contains a combination of uranium, plutonium, and fission products that can take somewhere between 10,000 and 100,000 years of decay to match the radioactivity of natural uranium</cite>. Numbers like that are hard to hold in your head, but they are the entire reason this is a policy problem and not just an engineering one. 📊
Do smaller reactors actually make less waste?
Here’s the part that surprises a lot of people, and honestly it surprised me too the first time I read the research. Smaller does not automatically mean less waste. In fact, some of the leading studies say the opposite. 🚨
A widely cited PNAS analysis looked closely at three advanced SMR concepts and found that <cite index=”47-1”>SMRs will likely produce more voluminous and chemically or physically reactive waste than large light water reactors, largely because their smaller cores leak more neutrons</cite>. That is a real physics problem, not marketing spin. Smaller reactor cores lose more neutrons out the edges instead of using them to split fuel, which means less efficient burnup and, in some designs, waste that is trickier to package and store per unit of electricity generated.
iPWR designs (like NuScale’s): waste volume and chemistry closer to conventional plants, but still scaled down per unit
Sodium-cooled fast reactors: more reactive waste streams that can complicate long-term packaging
Molten salt reactors: liquid fuel adds handling complexity, since spent fuel isn’t a neat solid rod you can just pull out
Not everyone agrees this is a fatal flaw. Advocates point out, reasonably, that <cite index=”56-1”>recent studies from Argonne National Laboratory and the National Academies found the amount of spent fuel produced by SMRs and microreactors will be comparable to waste from conventional reactors on a fleet-wide basis</cite>, and that some advanced designs are built specifically to burn down existing waste stockpiles rather than add to them. Oklo is probably the loudest example, marketing its Aurora design as running partly on recycled material. Whether that pans out at commercial scale is still an open question, and it’s one worth watching closely if you’re tracking which designs actually deliver on their waste claims versus which ones are still theoretical. 💡
Where does the waste actually sit right now?
This is the part that tends to shock people who assume there’s a “nuclear waste facility” somewhere quietly handling all of this. There isn’t. Not in the United States, anyway. 🏭
<cite index=”49-1”>The nation has over 90,000 metric tons of spent nuclear fuel from commercial power plants, and DOE is responsible for disposing of it in a permanent geologic repository but has yet to build one, because policymakers have been at an impasse over what to do with this fuel since 2010</cite>. That backlog isn’t shrinking either. <cite index=”49-1”>The amount of spent fuel stored at power plants keeps growing by about 2,000 metric tons a year</cite>, sitting in cooling pools and steel-and-concrete dry casks at reactor sites across the country. <cite index=”51-1”>Those 77 sites span 35 states, and they are increasingly becoming de facto permanent disposal facilities by default, not by design</cite>.
Why? The short version is Yucca Mountain. Congress picked the Nevada site back in 1987, Nevada fought it for decades on safety and political grounds, and the project effectively died under the Obama administration. Nobody has replaced it with a real alternative since. 🌍 A few private companies have tried to fill the gap with consolidated interim storage facilities in Texas and New Mexico, but <cite index=”53-1”>a federal appeals court ruled the NRC lacked authority to license a temporary storage facility not located at a nuclear plant or federal site, nullifying one of those licenses</cite>. So even the stopgap solutions are stuck in court.
How other countries are actually solving this
It’s worth zooming out, because the U.S. isn’t the only country wrestling with this, and some are genuinely further along. This is where the international comparisons get interesting. 🌎
Finland: the Onkalo repository near Eurajoki is the furthest along of any project worldwide, built 430 meters deep in bedrock roughly 1.8 billion years old
Sweden: SKB received government approval to construct a deep repository at Östhammar and began surface preparation work in 2025
Canada: selected the Wabigoon Lake Ojibway Nation-Ignace area in late 2024 as the site for its national repository
France, Switzerland: both pushing toward license applications for their own deep geologic sites
<cite index=”55-1”>These countries typically work through a stepwise process: a siting decision, then a license to construct, then a license to operate, and history shows the whole sequence can take decades</cite>. The common thread across the successful programs is patience and consent. Sweden and Finland spent years building trust with host communities before construction even started, which is basically the opposite of how the Yucca Mountain fight played out. If you want a running comparison of which countries are actually shipping fuel underground versus just talking about it, SMRbrief Pro members can search and filter that regulatory pipeline directly.
Is there a faster fix coming?
A few paths could ease the pressure sooner than a mined repository ever will, and none of them require waiting fifty years for consensus politics to sort itself out. ⚡
Deep borehole disposal: companies like Deep Isolation propose lowering waste canisters into narrow, directional boreholes drilled thousands of feet down, avoiding the enormous cost of excavating a mined repository
Fuel recycling and reprocessing: a recent executive order pushed to restart commercial reprocessing, aiming to shrink both the volume and radioactive lifespan of leftover material
Transmutation: converting some long-lived radioactive elements into shorter-lived ones, which could shrink the timescale a repository needs to hold waste safely
Consolidated interim storage: centralizing waste at one or two sites instead of 77 scattered ones, even without a permanent repository yet
None of these fully solves the problem on their own. <cite index=”51-1”>Storing spent fuel in pools and dry casks is safe for decades but not for the millennia needed to truly isolate it from the environment</cite>, so eventually something permanent has to get built, somewhere, with somebody’s consent. That is genuinely the hard part, and it has almost nothing to do with the reactor technology itself. 🔋
So here’s the real question worth sitting with: as SMRs multiply across more sites in more states, does that make the waste problem easier to solve, because smaller, more efficient designs eventually replace an aging fleet, or harder, because now there are more scattered locations each generating their own stockpile with nowhere permanent to send it? I don’t think the industry has a clean answer yet, and I’d bet the states currently courting SMR projects for their data center power demand haven’t fully reckoned with that tradeoff either. Worth asking your local utility commission before the ribbon-cutting ceremony, not after.