The area was completely sealed off to the outside world, and remains so today.

For 6 months following the accident, as the Sarcophagus was under construction, a team of courageous scientists from the Kurchatov Institute of Atomic Energy re-entered Unit 4 as part of an investigation aptly-named Complex Expedition.

“Everyone was afraid of one thing: an explosion might happen again, because the reactor was out of control” recalls Viktor Popov, the nuclear physicist in charge of the expedition. “Were conditions inside the reactor such that another catastrophe might occur?”

They explored the plant’s ruined and unpowered sub-levels with flashlights and cotton masks. “At that time,” says Popov, “there were no places in [Unit 4] that were not dangerous, not by normal human standards. We entered fields of 100, 200, 250 roentgens an hour. This kind of situation could crop up unexpectedly. You’re walking down a corridor and the levels are not too bad; 1 to 5 roentgens per hour. Then you turn a corner and suddenly it’s 500 roentgens! You have to turn and run for it.”

In December – six months after the accident – the group of scientists finally found some fuel, with the help of remote cameras poking through a long hole drilled into a wall. It was still emitting extreme radioactivity. “It made us treat it with the utmost respect,” remembers Yuri Buzulukov, another expedition scientist. “To approach it meant certain death.”

Here you can see the tops of the water pumps poking out of the debris.

The science team next needed a closer look at the reactor itself, so they brought in oil industry engineers to begin drilling through the reactor’s reinforced-concrete containment structure. They finally broke through in the summer of 1988, after the end of 18 months of drilling in harsh conditions. “There were many theories about what we might find there,” says Buzulukov, “but everyone agreed there would be damaged reactor core: graphite blocks interspersed with distorted fuel rods. But once a hole had been drilled in the side of the reactor vessel, the sight that met our eyes was totally unexpected. The reactor was completely empty.”

In 1991, the exhausted and stressed members of the expedition decided there was little alternative but to venture into what was left of Unit 4’s reactor hall to look for themselves – the risk of a possible second explosion was too great.

After clambering over shattered graphite blocks blown out of the reactor and shovelled off the roof, they discovered steaming concrete, heated by the fuel beneath it. Upon further inspection, they saw radioactive lava – an astonishing find. On their way back, as they passed through a shattered corridor adjacent to the bottom of the reactor, in an area of 1,000R/h, they saw that the lower biological shield had crushed the wall beneath it. The final missing piece of the puzzle fell into place.

This is what had happened on that fateful morning: the explosion that blew off the reactor lid also dislodged special serpentine sand and concrete from within the thick walls surrounding the RBMK. In that same moment, a powerful shockwave forced the entire bottom half of the core assembly – including the lower biological shield – downward by several meters into the space below.

Over the course of about a week, intense heat generated by the fire and beta decay gradually increased until it reached temperatures sufficient to melt the fuel assembly, which poured out and bonded with the sand/concrete mix to form a kind of radioactive lava called corium. This lava then passed through pipes, ducts and between cracks in the damaged structure to the rooms beneath.

This diagram illustrates the event, showing where the fuel came to rest.

A piece of the cooled lava/fuel. I don’t know how this man could have possibly approached it, so I assume this was probably taken around 1991, when it wouldn’t have been quite so lethal. Even then, he will have had to run into and out of the room immediately.

An image of the ruined turbine hull.

In 1987, global attention turned to the Soviet elite who faced the task of deciding who would be held responsible for the Chernobyl disaster, and what the appropriate response would be. Six men were put on trial in July, including (from front to back), Bryukhanov (plant manager), Dyatlov (Deputy Chief Engineer, and the man responsible for forcing the test to continue), and Nikolai Fomin, the plant’s Chief Engineer.

Soviet leaders were supplied information originating from V. P. Volkov, head of the Kurchatov Institute’s RBMK safety research group, which made it very clear that the accident was a result of critical design flaws, but the idea that Soviet reactors were anything less than perfect could never be admitted to the world. The USSR was founded on a belief in science and had always taken pride in being a technological superpower, there was fear among the Council of a possible public backlash against nuclear power, as had occurred in America after Three Mile Island.

The Chairman of the panel of judges had no interest in hearing about defects of the reactor. Scherbina and Legasov’s original government commission had discovered these defects and concluded that the reactor was at fault, but the only sections of their report given any credence by the judges were those criticising the operators. So-called ‘independent experts’ were, in fact, hand-picked men from the various Institutes responsible for the reactor’s creation in the first place – the very same men who had a vested interest in seeing their work exonerated.

Legasov took a very strong stance against the official story that the plant’s staff were entirely to blame. His resistance ruined his career. With his reputation in tatters, his health ravaged by the radiation he absorbed at Chernobyl, his disillusionment with his country’s unwillingness to focus more on safety, and feeling the weight of so many dead on his shoulders, he hanged himself on the second anniversary of the disaster – the day after his proposal for a reformed Soviet scientific community was rejected.

All six men were found guilty and sent to prison. Bryukhanov and Dyatlov were released early due to poor health. Chief Engineer Nikolai Fomin was declared insane in 1990, and transferred to a psychiatric hospital. Astonishingly, after he recovered he was allowed to return to work at the Kalinin Nuclear Power Plant near Moscow.

Meanwhile, Pripyat lay abandoned, and remains so to this day.

Over the years, animal mutations started to appear – DNA corrupted by the radiation.

None of the machines used during the operation to clean up the zone could ever be used again, as they had become highly radioactive. They lay in vast metal fields for years, before they were gradually taken away and buried in pits.

An image of the Unit 4 control console as it appears today.

The Sarcophagus was never intended as a permanent solution. Rather, the concern at the time was to erect a structure which would confine the radioactive release as rapidly as possible. As a consequence, it never fit together seamlessly and, in any case, only had an estimated life of around 20 years – a time frame which has long since expired. In 1997 a plan funded by 46 different countries and organisations for a replacement – dubbed the New Safe Confinement (NSC) – was set in motion with an estimated cost of €2 billion. Construction began in 2011. Here you can see the first section being raised.

The enormous, one-of-a-kind arch, 250m wide by 165m long, the NSC will weigh a colossal 30,000 tons, and is being assembled from prefabricated sections at a special holding ground 400 metres west of Unit 4. The first half was completed at the end of March 2014, as seen here. Upon completion of the second half, the two pieces will be combined and slid along purpose-built tracks over the existing Sarcophagus. It will be the largest movable structure ever built. Unlike the original Object Shelter, this new confinement has been built to last an estimated 100 years, by which time most of the decommissioning work on Unit 4 should be concluded.

As part of this operation, Chernobyl’s iconic chimney was removed last year.

Pripyat as it appears today. I visited the city in 2011, and found it to be a most profound experience. When I got back I began to research and write a book both about the accident and my own journey there.

The book came from my own frustration at the existing books on the subject, which I found very inaccessible for those unfamiliar with the topic and nuclear engineering in particular. I’ve now finished writing what I want to write, but I need to hire the services of an editor to polish it. I can’t afford to pay for this, so I’ve had to shelve the project.Since people have been asking me about it a lot today, I’ve decided to make it available for 24 hours as a physical book. You can find it here: http://blur.by/1Fo7zqg or here: http://blur.by/1FoaJtT for a hard cover version.

The book came from my own frustration at the existing books on the subject, which I found very inaccessible for those unfamiliar with the topic and nuclear engineering in particular. I’ve now finished writing what I want to write, but I need to hire the services of an editor to polish it. I can’t afford to pay for this, so I’ve had to shelve the project.Since people have been asking me about it a lot today, I’ve decided to make it available for 24 hours as a physical book. You can find it here: http://blur.by/1Fo7zqg or here: http://blur.by/1FoaJtT for a hard cover version.