hi kids, we’ll talk about one of the liquidation efforts of chernobyl today.
Background
On the 26th of April 1986, unit 4 of the Chernobyl Nuclear Power Plant (ChNPP) exploded during a safety test. As a result, hundreds of thousands of radioactive materials were released into the air, and the surrounding area became increasingly radioactive. After the disaster, the Soviet government decided to ‘liquidate (comes from ликвидация аварии)’ the area. This process was the clean-up and containment of the aftermath of the Chernobyl disaster. Some key examples include firefighters who first responded to the reactor fire, the operators of ChNPP, and the people who dug a tunnel under the reactor, which we will be discussing today.
Why did we need a tunnel?
After the Chernobyl disaster, Soviet Helicopters such as the Mi-8 and Mi-6 dumped a mixture of sand and boron into the exposed core of the remains of reactor 4 in a desperate attempt to suppress the fire, absorb neutrons, and cool the core. However, this brought a new problem. While it did cover the fire, the material acted like a thermal blanket, trapping heat and pushing temperatures in the reactor debris even higher.
A new fear grew that the molten core (“lava” of fuel + graphite + metal) could burn downwards (meltdown). This was not the major concern though, as beneath reactor 4, lay a large pool of bubbler pools, and deeper still, the natural groundwater table of the Pripyat River basin. If the molten corium (fuel + debris) reached this water, it could either cause a massive steam explosion*, or contaminate the Dnieper River system, which supplied water to much of Ukraine.
* There is no evidence of how big this explosion was estimated to be, due to conflicting information. There are some claims that a steam explosion at Chernobyl could have been mega-tone scale (comparable to a thermonuclear bomb). This figure was provided by multiple people like Vassili Nesterenko’s often quoted 3-5Mt figure, and this figure was often portrayed, but this claim is not supported by mainstream technical assessments.
To prevent such contamination/explosion, the Soviets decided to dig a tunnel under the reactor to cool the reactor from below.
Kiev’s Metro Construction Company
In early May 1986, a call from the governmental task force in Chernobyl contacted an office in Kiev. The headquarters of KyivMetroBud, the subway construction company. The caller told the head — Oleksiy Semenov — that due to the circumstances (mentioned above), a pit will be dug near Unit 3, where radiation levels were lower. Then, from this pit, some horizontal drills will dig until it reached an area beneath Unit 4. There, an immense amount of liquid nitrogen would be pumped in, stabilizing the sand and cooling the reactor from below.
The KyivMetroBud was chosen for this task as they did most of these tasks before. Kyiv’s metro system is located quite deep, and in fact, the Arsenalna Station remained the deepest subway station at 105.5m (346 ft) from 1960 to 2022 until Hongyancun station in Chongqing, China stole that record. And because these stations were built so deep, nitrogen freezing was a technique KyivMetroBud frequently used.
On scene, since nobody knew how deep the ground water level was situated in, a little digging was done up to 11 meters underground, and no groundwater was found, which meant they could continue with this operation without dewatering. Liquidators arrived in APCs across Unit 4, where radiation levels reached up to 1,500 Roentgen per hour.
On May 9th, the liquidators came across a problem. There were the leftovers of the cranes used to build the NPP from years ago blocking their path. Fortunately, the Minister of Transport of Construction at the time, Vladimir Brezhnev managed to get his hands on a remote-controlled Japanese Komatsu bulldozer. The next day, a drilling machine began the horizontal drilling. However, on May 16, Semenov gave the order to stop the drilling and return to Kyiv due to ‘some changes’.
At that time, scientists at the Kurchatov Nuclear Institute calculated that the situation was far worse than first imagined. So instead of drills pumping nitrogen underground, a long tunnel had to be built, with a chamber which measured 30m x 30m (100ft x 100ft). In said chamber, heat exchangers would be installed to cool the reactor more effectively. The Minister of Middle Machine Building took the job of installing the heat exchangers, and the digging of the tunnel to the miners, led by the Minister of Coal, Mikhail Schadow.
The Miners
^ Diagram by the Chornobyl Family 🇺🇦, showing the tunnel and heat exchanger pads underneath the damaged reactor number 4.
The tunnel, 136m long and 2m in diameter, had to be done without disturbing the structure above, and since they were working below heavy sand, the tunnel consisted of tubing, the same method used in subway construction. Inside the tunnel, radiation levels were normal, but it was as hot as 60 degrees Celsius (140 Farenheit), due to the amount of welds, and the vents were overwhelmed.
However, another discovery was made from the Kyiv institute. They made special thermal flux detectors and those detectors concluded that there was no risk of a further meltdown, which meant the operation could be stopped. Nevertheless, on June 24th, the heat exchangers were installed. Later on, the tunnel and the chamber was filled with concrete, turning it into another powerful barrier.
bye kids, stay safe.
DasBlog 
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