April 26, 2026, marks the 40th anniversary of the Chernobyl Unit 4 nuclear disaster in the former Soviet Union. This catastrophic event resulted from a combination of defective reactor design, inadequate safety analysis, neglect of operational procedures, prioritizing power production over safety, and, most notably, excessive secrecy, leading to the worst nuclear reactor accident in history.
During a safety test, operators mishandled procedures, causing the reactor to enter an unstable state. This led to a rapid power surge, triggering violent steam explosions that destroyed the reactor core and its surrounding structures. Fires raged for days, dispersing massive amounts of radioactivity across the former Soviet Union and much of Europe. Hundreds of thousands were evacuated or relocated from contaminated areas, and a 30-kilometer exclusion zone was established, which remains today. Dozens of emergency responders died from acute radiation syndrome, and thousands of children developed thyroid cancer due to radioactive iodine exposure. It is projected that tens of thousands of cancer cases across Europe will result from the radioactive fallout of the disaster.
The United States and many other countries have distanced themselves from the possibility of a Chernobyl-like incident by asserting that their nuclear regulators would not have licensed a reactor with the RBMK’s safety deficiencies. Light-water reactors (LWRs), the most common type of power reactor, are claimed to be much safer. Although this argument holds some truth, it became apparent after the accident that the safety advantages of LWRs compared to the Chernobyl-4 RBMK were not as significant as advertised, as evidenced by the 2011 Fukushima Daiichi triple LWR meltdown in Japan. Today, the US nuclear fleet’s regulatory requirements and standards are being undermined as the Trump administration aggressively moves to “unleash” nuclear energy swiftly.
It can’t happen here… or can it?
In the aftermath of the Chernobyl accident in April 1986, the US Nuclear Regulatory Commission (NRC), an independent agency overseeing commercial nuclear facilities, conducted a review of its implications for US nuclear power plant safety. The NRC concluded that such a catastrophe was unlikely to occur in the United States, citing several factors differentiating the Soviet nuclear approach from that of the United States and other Western nations. These included requirements for nearly leak-tight containment structures, strict limits on operation in unstable states, and emergency plans to protect the public during accidents. Therefore, the NRC determined that “no immediate changes are needed in the NRC’s regulations regarding the design or operation of U.S. commercial nuclear reactors.”
Although the NRC did not find its regulations inadequate post-Chernobyl, subsequent decades saw the agency pressured by the nuclear industry and lawmakers to relax its standards. This led to lax oversight, nearly resulting in a serious loss-of-coolant accident and potential meltdown at the Davis-Besse reactor in Ohio in 2002. The NRC had to slow down deregulation temporarily. Eventually, industry influence resulted in executive orders signed by President Donald Trump in May 2025, undermining the independent oversight established over 50 years ago when the Atomic Energy Commission was divided into the NRC and DOE.
More concerning developments are underway as the NRC rewrites regulations and guidance following EO 14300, “Reform of the Nuclear Regulatory Commission,” aimed at reducing safety and security standards to hasten new facility licensing and decrease oversight of existing ones. EO 14301, “Reforming Nuclear Reactor Testing at the Department of Energy,” instructs the DOE to expedite approval for three new nuclear reactors to reach “criticality” by July 4, 2026, demanding an unprecedented and reckless pace of construction and commissioning.
This disregard for learned lessons may lead to reactors being built across the US with similarities to Chernobyl. In March, the NRC granted a permit to TerraPower, co-founded by Bill Gates, to construct a 345-megawatt reactor called “Natrium” in Kemmerer, Wyoming. Despite lacking a containment structure and being vulnerable to rapid power increases, the Natrium uses liquid sodium coolant, which can catch fire, earning it the nickname “Cowboy Chernobyl.”
Chernobyl lessons: learned and unlearned
In 1989, the NRC reviewed the Chernobyl accident’s causes and issued a report titled “Implications of the Accident at Chernobyl for Safety Regulation of Commercial Nuclear Power Plants in the United States.” It identified areas needing attention, including reactivity accidents, low and zero power accidents, multi-unit protection, fires, containment, emergency planning, severe-accident phenomena, and graphite-moderated reactors. Today, the NRC, DOE, and nuclear industry are busy unlearning Chernobyl’s lessons, particularly regarding containment.
To contain (with a structure) or not to contain (with a structure)? That is the question
Ten years ago, on Chernobyl’s 30th anniversary, the NRC emphasized reactor containment’s critical role in ensuring US fleet safety versus the Chernobyl design. “U.S. reactors have containment buildings equipped with walls that are several feet thick and have a steel liner on the interior to help prevent the release of radioactivity during a severe accident,” NRC spokesman Neil Sheehan stated in a statement. “During the Three Mile Island Unit 2 accident, the containment structure served that function effectively.”
Yet, only two years later, the NRC abandoned its principle that “reactor containment and associated systems shall be provided to establish an essentially leak-tight barrier against the uncontrolled release of radioactivity…”. For new non-light-water reactors, like the Natrium using coolants other than water, the NRC allowed approval of designs without traditional containment structures, accepting “functional” containments instead. This regulatory rollback lets reactor applicants substitute physical containment with other design features.
Alongside the Natrium, another non-light-water reactor without containment is the Xe-100, an 80-megawatt, “pebble-bed” high-temperature gas-cooled reactor (HTGR). Its developer, X-energy, plans to build four Xe-100s next to a Dow chemical plant in Seadrift, Texas. Unlike LWRs, these reactors use “tri-structural isotropic” (TRISO) fuel, touted as “the most robust fuel on Earth” by the DOE. X-energy and other HTGR developers claim this fuel negates the need for physical containment.
However, a legal filing prepared for a petition by San Antonio Bay Estuarine Waterkeeper against the Xe-100 construction permit reveals that TRISO fuel is not as robust as claimed, with significant uncertainties about its performance in certain accidents. X-energy’s own accident analysis shows the fuel could exceed the maximum safe temperature by several hundred degrees Celsius. The company has not yet demonstrated that the reactor can be safely operated without containment.
X-Energy has only recently started a multi-year testing program to address fuel performance uncertainties. Nevertheless, the NRC appears ready to allow containment-less design construction to proceed before obtaining testing data. Even if the fuel performs worse than expected, it’s unlikely the NRC would require costly retrofits to add containments before operation.
Why would the NRC disregard the safety benefits of physical containments? The answer is cost. Physical containment structures, requiring large amounts of high-quality reinforced concrete, are expensive. A 2020 MIT study noted containment as a major cost contributor for light-water reactors. Eliminating containment is a quick way to reduce nuclear project costs. For new reactor types and models, such as small modular reactors, physical containment is impractical and unaffordable.
Eliminating physical containments is a short-sighted method of reducing nuclear power costs, as demonstrated by Chernobyl. Functional containment is not an adequate substitute. One primary role of containment is to provide “defense-in-depth,” an extra assurance level to compensate for gaps in understanding reactor behavior during accidents. For new reactor designs with limited or no operating experience, understanding is lacking, and predictions are uncertain. Thus, containment’s role in mitigating unknown risks from experimental designs is crucial.
The NRC is approving functional containments for new reactors, like the Natrium and Xe-100, based on paper safety studies lacking real-world validation. Applicants can exclude accident scenarios from safety analyses that might demonstrate the need for physical containment, assuming they are too improbable to consider. This approach mirrors Soviet review methods when approving the Chernobyl design with partial containment.
The NRC’s 1986 Chernobyl review noted that “credible accidents with potentially serious consequences” were not included in the Soviet safety analysis, likely deemed too improbable to warrant design inclusion. These included “rapid reactivity excursions” and other sequences that occurred during Chernobyl. The report mentioned that only considering pipe breaks below the reactor as credible resulted in no containment surrounding the outlet piping above the reactor.
This reasoning is familiar to those acquainted with the “risk-informed” regulatory approach the NRC recently approved for new reactor licensing, which addresses questions like functional containment adequacy. The new 10 CFR Part 53 rule, issued in March, allows applicants to use “probabilistic risk assessments” or “systematic risk evaluations” to develop the accident sequence spectrum for licensing. The lack of guidance for “systematic risk evaluation,” including a standard for worst-case accident determination, allows for subjective cherry-picking similar to Soviet methods, justifying the lack of full containment.
The NRC’s approval of the Natrium and likely approval of the Xe-100 set dangerous precedents for future reactor proposals, most of which lack containment designs. However, minimal new nuclear plant construction has occurred, providing the NRC ample opportunity to change course before irreversible mistakes occur. On Chernobyl’s 40th anniversary, the NRC should reflect and reconnect with its 1989 conclusion that the “most important lesson [of Chernobyl] is the continuing importance of safe design in both concept and implementation…and of backup features of defense in depth against potential accidents.”
This week also marks the 20th anniversary of my own visit to see the devastation within the Chernobyl exclusion zone, which is seared into my memory. If anyone still needs convincing that it’s a terrible idea to allow reactors without real containment structures to be built across the United States, I highly recommend the Chernobyl tour (once the war is over of course).
