Even nearly 40 years after the most destructive nuclear accident in human history, the graphite reactor (RBMK) is no distant relic. As of 2023, there are still eight in operation. For us in the modern world, what are the possible uses of such an old nuclear reactor? To understand why people think this way, we need to understand what kind of machine we're dealing with, and what makes it so deadly. We are all more or less familiar with the principle of fission. Atoms split and emit free subatomic particles that strike other atoms and cause them to split as well. And that's not even getting into the nitty-gritty. Much to the Soviets' delight, the RBMK reactor does not need heavy water to operate. This means that in Chernobyl reactor 4, the dangerously supercritical fissile fuel core came into contact with ordinary water. To make matters worse, the boron carbide control rods were in a fully raised position. The resulting superhot steam pushes the pressure beyond what the facility can handle.

The heat of the reaction caused the elements of the water to separate, producing hydrogen and oxygen that blew the lid off the reactor. Two powerful explosions in succession caused the graphite material to turn into a molten substance. The resulting radioactive lava seeped through metres of concrete before settling in basement rooms in the reactor facility. In addition, there are some other side effects.

This is, of course, a simplification of the Chernobyl nuclear accident of April 1986.

Engineers need to do some engineering to make sure the fission doesn't turn into an uncontrollable chain reaction. Using moderator materials, engineers can use compounds such as graphite to deliberately block the flow of free neutrons thrown off during fission. And the fuel is further cooled by liquid coolant. Most of the time, the coolant is water or heavy water.

As one of the best liquid moderator/cooling materials known to science, heavy water is paid dearly for by nuclear facilities around the world, but not RBMK. RBMK is designed to be a low-cost fission reactor class that runs on low-quality fissile fuel, and industry-standard uranium 235 is most commonly used to fuel RBMK reactors, as was the case at Chernobyl.

These reactors use much lower levels of enriched uranium than, say, Canada's CANDU-class reactors. Coincidentally, CANDU has a far better public reputation than RBMK and is used worldwide. RBMK uses uranium enriched to as little as 1 or 2 per cent, compared with up to 4 per cent in Western reactors. We haven't even touched the RBMK 1000's ridiculously high positive void coefficient. Essentially, free neutrons build up in the void of the steam bubble heated by the nuclear fuel, and the fuel rods easily enter a supercritical state. Essentially, the less water there is in the core of the pile, the more likely it is to explode.

Lower operating costs with poor refined uranium and a lack of heavy water, combined with plant management's overconfidence in the RBMK 1000 series, set the stage for disaster. The accident investigation proved that the reactor did not even have enough control rods to improve conditions in the supercritical fissile core, which was on the verge of meltdown.

Many Westerners first encountered RBMK fission reactors not because of the Chernobyl accident itself, but because of the 2019 hit HBO series "Chernobyl." While the five-part miniseries is fascinating, it doesn't explain much in the aftermath of the disaster.

First, only the fourth reactor at the plant had an accident. Reactors 1 to 3 continued to operate into the late 1990s. By 2000, RBMK was completely retired and ready for decontamination. But after the Chernobyl accident, RBMK reactors continued to develop. Even before the Chernobyl accident, upgraded RBMK 1500 series reactors were in operation and continue to be deployed in Eastern Europe.

The first RBMK built outside the Soviet Union was at the Ignalia nuclear power plant in Lithuania. At its peak, Ignalia provided a quarter of Lithuania's electricity. Although it was decommissioned in 2009, Ignalia's RBMK reactor ensured Lithuania's smooth entry into the nuclear age.

In Russia, the Kursk nuclear power plant uses a RBMK-1000 reactor that is essentially the same as the one at Chernobyl since 1977. While the first reactor is shut down in 2021, the remaining two to four reactors will continue to operate until at least 2030. There are two more RBMK facilities in Russia, one in the Smolensk region and one in Leningrad, which are not due to expire until 2034 at the earliest.

It is understandable to be alarmed to learn that there are still eight potential Chernobyl disasters in 2023. But before you despair, consider this. From 1986 to 2023, after a fatal accident in Ukraine, none of the RBMKS in operation had a supercritical fission accident at all. Only after the critical power of this brand fission was fully understood did the safety record of the RBMK reactor begin to level off.

After the Chernobyl disaster, contingency plans for critical events (such as high xenon concentrations when reactor pumps are not working) were put in place. As with the introduction of fissile control rods in the RBMK-1500 series reactors, the core can be quickly introduced in the event of a Chernobyl-like accident. In this case, the ending number is the reactor's rated capacity, in megawatts. The modification features a customized "Emergency Core Cooling System" (ECCS) that continuously pumps cooling water into the core even during safety tests when the main pump is not working.

Most importantly, the little devil with the high positive void coefficient was reduced to a more manageable level. As a result, its post-1986 safety record was the opposite of its global reputation. As the HBO miniseries is eager to point out, there was also a fair degree of administrative oversight on the night of the accident. The show's portrayal of Anatoly Dyatlov, the factory's deputy chief engineer, as an almost comically evil and sadistic man with no regard for worker safety is certainly played up for the sake of a good story. Yet his team's negligence on the night of the Chernobyl disaster cannot be underestimated. How different history's view of the RBMK reactor might have been if the events of that night had been just a little different. Will the world even know about a small, unremarkable city in a Ukrainian forest? Would the Soviet Union have even collapsed without such a disaster leaving doubt in the public mind? We can only imagine how different the world would be today.

For now, the RBMK reactors still have a little time before they are all taken out of service and relegated to the history page. Despite the massive destruction that took place at Chernobyl. But what we've seen over the years is that nuclear power has caused far fewer deaths than petrochemicals.