The 5 Biggest Arguments Against SMRs — And How Proponents Answer Them
Critics have real ammunition — but the case for small modular reactors is tougher to dismiss than its loudest opponents would like.
Every technology that threatens to rearrange the energy order gets hit with the same barrage: it’s too expensive, too slow, too dangerous, too unproven. Coal said it about natural gas. Oil said it about coal. And right now, a coalition of skeptics — environmental groups, anti-nuclear academics, and some very credentialed economists — is making the same case against small modular reactors. Some of those arguments land. Others don’t. Most fall somewhere in the uncomfortable middle.
The honest answer to the question “Are SMRs viable?” is: it depends on what you’re comparing them to, and what problem you’re actually trying to solve. So instead of pretending this debate is simple, let’s lay out the five strongest objections to SMRs and give proponents a fair chance to respond. You can decide who has the better of the argument.
Argument 1: SMRs cost more than renewables and can’t compete 💸
This is the one critics return to most often, and they’re not wrong about the numbers. According to the International Energy Agency, SMR overnight costs in the EU run around $10,000 per kilowatt — compared to roughly $6,600 per kW for traditional large nuclear. Wind and solar have fallen so far in cost that stacking SMRs against them looks almost unfair. A 2023 ScienceDirect study estimated the median levelized cost of electricity for SMR designs at over $200 per megawatt-hour, while onshore wind typically comes in between $26 and $50 per MWh.
The collapse of NuScale’s UAMPS project in late 2023 handed critics a real-world data point. The project’s final cost per megawatt was roughly 250% higher than initial estimates — a painful lesson in first-of-a-kind economics.
The proponent response has several layers:
First-of-a-kind costs always look like this. Every technology, including solar panels and lithium-ion batteries, was absurdly expensive before manufacturing scale drove prices down. “Nth-of-a-kind” projections for SMRs are considerably lower.
Financing terms change the equation. A GLOBSEC analysis showed that a conventional nuclear plant taking 15 years to build could end up more expensive in total cost than a 5-year SMR build, even at a higher overnight price, because interest accumulates more slowly over shorter construction periods.
Renewables can’t do everything. Wind and solar are intermittent. SMRs are dispatchable, meaning they generate power on demand, around the clock. Pairing renewables with enough storage to cover extended low-wind, low-sun periods is also extremely expensive — that cost rarely shows up in the headline comparisons.
The critics aren’t wrong. But “more expensive than wind” is not the only frame that matters.
Argument 2: SMRs take forever to build — too slow to matter ⏱️
JP Morgan’s 2025 energy report found that the four SMRs built globally — in China, Russia, and Argentina — had construction timelines planned at three to four years, but all took roughly 12 years to complete. Argentina’s project had cost overruns of 700 percent at last count; China’s and Russia’s came in 300 and 400 percent over budget, respectively.
If the goal is slashing carbon emissions by 2030, an SMR that takes 12 years to build from groundbreaking is not a climate solution for this decade. That’s the critics’ sharpest point, and they’re right to make it. 🌍
Proponents concede the construction timelines on existing reactors and pivot to several rebuttals:
Those early builds were essentially one-off, first-of-a-kind units with no supply chains, no trained workforces, and no regulatory precedent. Each one started from scratch.
The U.S. ADVANCE Act of 2024 has already streamlined NRC licensing reviews, cutting target timelines to 36 months.
Companies like Last Energy and Kairos Power claim 24-month module delivery timelines. In October 2024, Google signed a deal with Kairos Power for a fleet of SMRs, with the first unit targeted for operation by 2030.
Unlike large reactors, phased commissioning is possible: you can bring one SMR module online while others are still being built, generating revenue during construction rather than waiting for a multi-billion-dollar plant to reach completion.
Whether any of this ambition translates into actual 36-month builds on U.S. soil remains to be seen. I think the optimists are probably too optimistic about timelines — but the pessimists are comparing future SMRs to first-of-a-kind prototypes, which isn’t a fair comparison either.
What’s your read? Do you think the speed argument sinks SMRs, or does phased deployment change the calculus?
Argument 3: SMRs produce more nuclear waste per unit of energy ☢️
This one surprised a lot of people when it landed in 2022. A Stanford and University of British Columbia study published in PNAS assessed three SMR designs and found that the waste management burden exceeded that of a comparable large pressurized water reactor by factors of 5 to 35, depending on the design. The reason is physics:
SMR cores are smaller, which means more neutron leakage
More neutron leakage means less of the fuel gets consumed, leaving more fissile material in spent fuel
More fissile material in spent fuel means you need more storage canisters — and stricter criticality safety measures in a repository
Some advanced designs, particularly non-light-water reactors, produce waste streams that are chemically and radiologically different from what existing regulatory frameworks were built to handle
This is not a frivolous concern. Higher neutron leakage in SMRs results in lower burnup, leaving more fissile material in spent nuclear fuel and increasing the waste volume. It also means a larger number of spent fuel canisters are needed in a deep geological repository to avoid criticality accidents. 🔬
Proponents push back on several fronts:
The PNAS study was based on partial design information, since most SMR designs are proprietary. Terrestrial Energy’s CTO publicly challenged the methodology within days of publication, citing what he called “numerous and significant factual errors.”
The DOE is actively funding programs specifically targeting this problem. The CURIE initiative and the ONWARDS program have distributed tens of millions in grants to research teams — including $8.5 million to TerraPower — working on spent-fuel recycling and waste minimization.
Some advanced fast reactor designs are explicitly designed to consume existing stockpiles of spent nuclear fuel as fresh fuel, potentially turning a liability into a resource.
A comparison that focuses on waste volume rather than waste hazard duration may be misleading. Smaller quantities of longer-lived isotopes don’t automatically mean a worse outcome than larger quantities of shorter-lived ones.
The waste argument is real. It’s also more nuanced than “SMRs make more waste,” and the industry knows it has to solve this before regulators and the public will play ball.
Argument 4: More reactors means more proliferation risk 🔐
A nuclear renaissance would mean more nuclear facilities, more nuclear material in transit, and likely more facilities for enriching uranium fuel. This increase could create greater opportunities for theft, diversion, or illicit activities, amplifying risks of nuclear terrorism and proliferation.
That comes from the Carnegie Endowment for International Peace, not exactly a fringe outfit. The concern is logical: if hundreds of SMRs are eventually deployed globally — including in countries with less robust regulatory institutions — the surface area for proliferation risk grows. Several advanced SMR designs also require high-assay low-enriched uranium (HALEU), which is enriched to higher levels than conventional reactor fuel, bringing it closer to weapons-usable material.
Critics note:
Transporting fuel and waste to and from hundreds of dispersed small reactors multiplies security exposure compared to a smaller number of large, heavily guarded central plants
HALEU fuel represents a meaningful upgrade in proliferation risk compared to the low-enriched uranium used in conventional large reactors
Countries that don’t currently adhere to strict IAEA safeguard standards could receive SMR technology through export markets, with uncertain enforcement
The proponent rebuttal:
SMRs are physically smaller and some designs are intended to be sealed, factory-fueled, and returned for refueling without the host country accessing the fuel cycle at all — essentially eliminating local enrichment needs
The U.S. and IAEA are explicitly requiring that new SMR designs integrate safeguards from the design phase, not as an afterthought
Millions of tons of nuclear waste and fuel are already transported across the U.S. annually, with a track record of zero successful theft or diversion
The Carnegie Endowment report itself acknowledges that new designs could mitigate these risks if security features are baked in during engineering
The honest position: proliferation risk is a design problem, not an inherent SMR problem. Whether the industry addresses it seriously enough in practice is a legitimate open question.
Argument 5: Public fear of nuclear is a dealbreaker 😰
You can win every technical argument and still lose the political one. Chernobyl happened in 1986. Fukushima happened in 2011. Neither involved SMRs, and neither involved the passive safety systems that modern reactor designs incorporate — yet public memory doesn’t sort by reactor type. According to Wikipedia’s SMR overview, 127 modular reactor designs are currently in development globally, but the gap between design activity and actual construction permits tells the story of a technology that has to fight hard for permission to exist.
The public opposition playbook typically runs through:
Not-in-my-backyard resistance from local communities selected as potential sites
Environmental justice concerns about where SMRs are sited and who bears the risk
Lingering association with weapons programs and Cold War dread
Distrust of the nuclear industry’s cost and timeline projections, given the track record
Proponents have a few responses that actually cut through:
Modern SMR designs rely on passive safety systems — gravity, convection, and natural circulation — that can shut down safely without any operator intervention or external power. The failure modes of a BWRX-300 or a NuScale VOYGR are genuinely different from those of a 1970s boiling water reactor.
The emergency planning zone for some certified SMR designs can be significantly smaller than for large reactors, reducing the scope of evacuation planning and, potentially, community opposition.
Big Tech buying in matters to public perception. When Google, Microsoft, and Amazon are signing long-term nuclear power purchase agreements, it signals a level of institutional confidence that’s hard to dismiss as propaganda.
Younger generations show measurably more openness to nuclear energy than their parents’ cohort, particularly when climate change is the framing.
Fear is not irrational given the historical record. But the risk profile of next-generation SMRs isn’t the same as Chernobyl’s RBMK reactor, and letting the past make all the decisions about the future seems like a mistake.
So where does this leave us?
None of the five arguments against SMRs is a knockout blow, and none of the responses is a complete vindication either. What this looks like, in 2025, is a technology at the end of its design-and-development phase — as the ITIF put it in its April 2025 realist assessment — with leading-edge designs preparing for first-of-a-kind deployment. Whether that deployment actually happens on time, on budget, and with the waste and safety outcomes proponents claim will determine which side of this debate history validates.
The critics are right that SMRs aren’t a silver bullet. The proponents are right that dismissing the whole category based on first-generation prototypes is intellectually lazy. The truth is that we don’t yet know which specific designs will survive contact with reality — and we won’t for at least a decade.
Here’s the question worth sitting with: if you were designing an energy portfolio for a planet that needs reliable, around-the-clock, carbon-free power for AI data centers, remote communities, and industrial processes — and wind and solar were already deployed at maximum practical speed — would you build the SMR option into that portfolio or leave it out entirely? Your answer to that probably tells you more about how you weigh risk, uncertainty, and timescale than any individual technical argument does.