The history of nuclear power has been a continuous journey towards safer designs. Small Modular Reactors (SMRs) represent a gigantic leap forward as they are designed to be inherently safe. By following the principles of “passive safety”, they rely on natural forces rather than the complex machinery and human intervention generally required by larger nuclear plants.
Nuclear accidents can be catastrophic, and incidents like Three Mile Island in 1979 and Chernobyl in 1986 highlighted vulnerabilities in complex active safety systems. These events underscored the need for designs that better prevent accidents, even under extreme circumstances.
This pursuit of safety in traditional, large-scale nuclear power plants led to the principle of “defence in depth”, which involves multiple independent and redundant layers of protection to prevent accidents and mitigate consequences. It has significantly increased the safe operation of reactors, but the sheer size of these facilities means that some of the safety features require external power or employees actively operating controls.
SMRs are largely taking a different approach: “passive safety.” Unlike traditional systems, these designs use gravity, natural circulation, and convection to cool the reactor. This means SMRs can safely shut down and cool themselves without any human action or outside electricity. It’s a game-changer, preventing problems from escalating before they even begin.
Many advanced SMR designs showcase this powerful shift. Some light water reactor designs, for instance, can self-cool indefinitely or for at least seven days, relying on natural circulation of water and large containment pools to dissipate heat through convection and gravity.
Other innovative designs utilize liquid metal coolants, such as sodium, which enable cooling through natural convection and typically operate without high pressure. Such designs simplify the entire system, making reactors far less susceptible to failures and human error.
A remarkable example of passive safety is TRISO (Tristructural-isotropic) fuel. This innovative product embeds multiple protective layers around each tiny particle of uranium. These layers act as miniature containment vessels, designed to “fail safe.” Even if a reactor faces extreme conditions, TRISO fuel can withstand temperatures above 1600°C, keeping radioactive materials securely locked inside and preventing core meltdowns. This built-in safety dramatically reduces any potential for off-site release.
The “passive safety” design philosophy has significant advantages when it comes to where SMRs can be installed. As they bring greater inherent safety, regulators are considering allowing much smaller Emergency Planning Zones. This means SMRs can be located closer to where power is consumed–like decommissioned fossil fuel plants, remote communities, or industrial sites–reducing the need for costly, long transmission lines.
SMRs are an essential component of our future energy mix. They bring clean, always-on power with a small footprint and generate significant local economic benefits. But perhaps most importantly, they are designed with a deep commitment to operating safety, ensuring that they bring only positives to the communities they serve.
