It is not well known that a team of coal miners in the former Soviet Union risked their long-term health by playing an integral part in the dangerous task of safemaking, containment and legacy preparatory works following the 1986 nuclear power plant disaster at Chernobyl, in what is now the independent territory of Ukraine.

The power plant’s Reactor Number 4 light-water graphite-moderated nuclear reactor catastrophically overheated, leading to an explosion and a subsequent open-air graphite fire, thereby releasing radioactive isotopes into the atmosphere for about nine days.

What was supposed to have been a regular systems test turned into one of the most notable nuclear accidents, as several safety precautions had been overlooked and overheating of the reactor core spiralled beyond the control of plant technicians and immediately available plant resources, such as a key emergency core-cooling system that had been disabled.

To date, the Chernobyl disaster remains the world’s worst nuclear power plant accident, considering the cost and casualties incurred. According to the International Nuclear Event Scale, it is one of only two such incidents classified as a Level 7 event (the highest classification), with the Fukushima Dai-ichi nuclear disaster, which occurred in Japan in 2011, being the other.

After the Chernobyl explosion, thousands of nonpower-plant workers – called ‘liquidators’ – were rushed to the plant. Among them were about 400 mineworkers who were called up from coal mines and tasked with excavating a tunnel directly underneath the core of Reactor Number 4.

The primary purpose of the tunnel was to facilitate liquid nitrogen being pumped into the remnants of Reactor Number 4 to cool the nuclear fuel and prevent destruction to the base of a new shelter that was soon to be constructed over the damaged reactor. The shelter – ominously referred to as the sarcophagus – was intended to contain the radioactive material that was leaking into the environment and atmosphere.

The tunnel dug by the coal miners would also serve to mitigate radioactive exposure to an underground aquifer below the reactor.

The team concluded their digging of the 168-m-long tunnel below the reactor 60 days after the disaster, on June 24. Helicopter pilots simultaneously dumped 5 000 t of lead, sand, clay and other material directly into the exposed Reactor Number 4 to douse the flames and reduce radioactive plumes emitting into the atmosphere.

The liquidators are widely credited with limiting the immediate and long-term damage of the disaster.