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How world class engineers are containing the danger of reactor number 4.

01/10/2018
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Some of the greatest feats in engineering are achieved out of a need solve an impossible problem. Chernobyl is the world’s biggest, most well-known nuclear disaster. But what exactly happened? And what solutions are pioneering engineers continuing to implement more than 30 years later to prevent any more radioactive leaks in to the atmosphere?
Chernobyl Nuclear Power Plant was located in a small purpose-built town in Northern Ukraine, named after the river Pripyat that ran alongside it. It was known as the ninth nuclear city within the Soviet Union. 

New Safe Confinement at Chernobyl

The evening of the 26th April 1986 began with routine safety drills and other tests, including the simulation of a station black-out power failure which involved safety systems throughout the plant being intentionally switched off. Unfortunately, a failure of operators to stick to the simulation checklist coincided with a series of errors caused by design flaws in reactor number four. Uncontrollable reactions led to a steam explosion, engulfing the reactor and eventually leading to an open-air graphite fire. This fire propelled plumes of fission material in to the atmosphere for 9 days. 

The incident was the worst nuclear disaster ever recorded at the time and led to over 45 deaths and countless health problems for future generations. 

In order to contain over 200 tons of radioactive FCM (fuel containing material), 30 tons of highly contaminated dust and 16 tons of Uranium and Plutonium, a structure called the Shelter Object was built. It was also commonly known as the Sarcophagus. 

Having held the materials in check for over 30 years, the Sarcophagus began to degrade, and repairs were needed. However, the radiation level in the reactor was estimated to be around 10,000 Rontgen’s per hour (500 Rontgen’s is considered a lethal dose over a 5-hour period). Safely repairing the Sarcophagus was ultimately ruled out as an option. 

The only available solution was to build a new confinement structure. The NSC (New Safe Confinement) was devised with the purpose of achieving four main goals: 
Prevent the release of radioactive contaminants.
Protect the reactor from external influences.
Facilitate the disassemble and decommissioning of the reactor.
Prevent water intrusion.

It was decided that the NSC would require a containment lifespan of 100 years, and the budget was set at a staggering $2.5 billion. 

Construction of the NSC was one of the most ambitious engineering projects ever undertaken. The arched structure is built from steel with an internal height of 92.5 metres (303.5 ft), an internal span of 245 metres (803.8 ft) and an overall length of 150 metres (492.1 ft). And as if that weren’t enough, the entire thing had to be built offsite – 180 feet away from the actual reactor – due to the risk posed to workers. 

The process of assembly had 9 stages: 
1. Stabilisation of the Sarcophagus to prevent collapse during construction. 
2. Excavation and construction of the foundation. 
3. Assembly of the first and second arches to form Bay 1, installation of east wall on arch 1.
4. Bay 1 slid East to accommodate the construction of arch 3 and Bay 2. 
5. Subsequent sliding of the complete structure and adding of arches and bays.
6. Installation of cranes and large maintenance equipment.
7. Installation of west wall.
8. Final slide in to place over reactor
9. Deconstruction of the fragmentation, decontamination and auxiliary buildings.

Stage 8, the final slide in to place, began on November 14th 2016 and completed on November 29th. Once the structure was in place, the pioneering air cooling systems were activated. These systems presented another challenge – if any condensation formed it would be contaminated, causing drops of radioactive liquid in the structure and risking corrosion. To solve the issue, engineers came up with a simple yet elegant solution. Warm, dry air is circulated in the gaps between the inner and outer sections of the structure to prevent any condensation forming.  

As of 2018 the NSC is the world’s largest moveable land-based structure, and provides hope to the people in the surrounding areas of Chernobyl for a safer environment. Out of one of the world’s biggest man-made disasters came an extraordinary engineering feat that will inevitably become the foundation for huge projects in the future. 

A true testament to the genius of the worldwide engineers who all played a part in this staggering, complex design. 

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How world class engineers are containing the danger of reactor number 4. - Time to read 4 min
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