Almost four decades after the most disastrous nuclear accident in history, the high-power channel-type reactor (RBMK) is far from being a distant memory. As of 2023, seven such reactors are still in operation.
Reactor 1 at the Kursk I nuclear power plant was shut down a year ago. However, seven other aging RBMK reactors continue to operate across Russia. Additionally, two similar RBMK-1500 reactors were constructed at the Ignalina nuclear power plant in Lithuania before being decommissioned by the European Union due to their age and potential danger.
The RBMK Reactors
RBMK reactors, or "large power channel reactors," are the technological foundation of the Chernobyl nuclear power plant. These reactors suffered from construction and operational shortcomings that were exacerbated to boost performance. They were central to the Soviet Union's nuclear energy program, the so-called "Atom Mirny" (Atoms for Peace), which had both civilian and military purposes – including the production of plutonium for atomic fission warheads and as the core of thermonuclear fusion bombs.
RBMK reactors are cooled by pressurized water flowing through channels while using graphite rods to moderate the fission reaction. These rods control the fission of natural uranium, which has a modest enrichment level. Due to their lower construction and operational costs, RBMK reactors can generate significant power without requiring highly enriched uranium. However, these reactors exhibited instability issues due to the "positive void coefficient," meaning that the nuclear reaction increased with temperature rather than decreasing.
Furthermore, the Chernobyl reactor had design flaws in its control rods, and the plant lacked an adequate protection system. The only protection was a concrete armor shielding the metal structure of the main vessel, which was sealed and filled with inert gas to prevent the reactor's graphite from contacting oxygen and causing an explosive chemical reaction – which, regrettably, did happen. After the Chernobyl disaster, modifications were made to increase stability, such as raising the fuel enrichment level from 2% to 2.4%.
The RBMK-1000 reactors used by the Kursk NPP closely resemble those at Chernobyl. Although the first reactor has been decommissioned, reactors two to four will continue operating until at least 2030.
The knowledge that potential Chernobyl-like disasters still exist in 2023 is undoubtedly alarming. However, experts point out that between 1986 and 2023, no supercritical fission accidents have occurred at any RBMK reactors operating post-Chernobyl.
Is this information enough to quell our concerns? Not quite.
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