4 40 years after Chernobyl – insights into reactor design

The reactor that exploded in Chernobyl was an RBMK, a Soviet design from the 1960s and 1970s. It was one of only two reactor concepts that were built on a large scale in the Soviet Union at the time.

The RBMK reactor had several fundamental design flaws in terms of safety, and even when it was built did not meet current Western safety standards.

Following the explosion, technical shortcomings in existing RBMKs were addressed. Moreover, the disaster led to much stricter international oversight, improved safety cultures and more transparency at nuclear facilities around the world. A few RBMK reactors are still in operation in Russia today.

Belgium's reactors are PWRs (Pressurised Water Reactors). This reactor type is the most commonly used around the world.

PWRs are based on a fundamentally different safety philosophy to that of the Soviet reactors. Safety is not an additional system, it is built into the physics of the reactor and the way it is operated. Key characteristics include:

The Chernobyl nuclear disaster also marked a significant turning point for Belgium. The accident highlighted the urgent need for independent oversight and led to the establishment of the Federal Agency for Nuclear Control (FANC). In 1988, our country also set up the National Crisis Centre (NCCN), responsible for coordinating emergency situations, including nuclear incidents.

Read more about emergency planning, regulation and oversight in Belgium.

Subsequent accidents, such as Fukushima, further intensified this focus on safety. They resulted in additional safety analyses and the introduction of stress tests: systematic safety tests designed to verify whether a nuclear power plant continues to operate safely even under extreme and unlikely circumstances — such as serious natural disasters, prolonged power outages or loss of cooling.

More on stress tests in the wake of Fukushima.

Chernobyl significantly slowed the growth of nuclear energy, both nationally and internationally. It led to a decline in trust on the part of the public, prompting many countries to pause or halt their nuclear programmes. In Belgium too, the accident strengthened calls for a Belgian nuclear phase-out. The perception of nuclear energy shifted from a ‘cheap, safe energy solution’ to a ‘source of potential catastrophe’. The debate over the risks of nuclear energy flared up and ultimately led to Belgium’s nuclear phase-out in 2003, which called into question extending the lifespan of the existing power stations at Doel and Tihange, and prohibited the construction of new nuclear power plants.

More than 20 years later, in 2025, Belgium amended this law once again. The most recent reactors (Doel 4 and Tihange 3) could stay operational for longer, and the ban on new nuclear activities was lifted. This also paved the way for new nuclear reactors, such as small modular reactors (SMRs).

The revision of Belgium’s nuclear phase-out in 2025 marked a clear change of course. Whereas nuclear energy was being phased out for many years, there is now renewed scope for nuclear innovation. 

In this context, Small Modular Reactors (SMRs) are attracting increasing attention: smaller, modular nuclear reactors that can be built in series, are flexible in their use, and with a strong focus on so-called passive safety systems right from the design phase. This means that, in emergency situations, the reactor can dissipate residual heat without an external power supply or active intervention. These systems utilise the gravity of the coolant.