How A New Sarcophagus Over The Old Made Chernobyl Safer
The Chernobyl power plant disaster was the world’s first level 7 nuclear accident, and also the most deadly. During a routine power outage simulation on 26th April 1986, reactor No. 4 exploded. This caused an open-air graphite fire, which burned unchecked for nine days. Twenty-eight emergency workers or liquidators died within months of the accident. Many thousands more succumbed to cancer and radiation sickness over the following years.
As an initial response to the emergency, a massive steel and concrete sarcophagus was built to encase the stricken reactor. Before construction could begin, 400 coal miners had to dig a 168m tunnel under the reactor to install a cooling slab. Liquid nitrogen was pumped in to cool the hot nuclear fuel before it could burn a hole in the base of the reactor.
Construction of the sarcophagus finished in November the same year. 400,000 cubic metres of concrete were poured into the structure, encasing tonnes of radioactive material inside. The installation of 60 bore holes allowed periodic inspection of the interior.
The original sarcophagus is supported by the reactor building, which was damaged in the explosion. Two major beams, B-1 and B-2, support the roof of the shelter. They rest partly on the cracked west buttress wall, itself stabilised by steel cantilevers. The sarcophagus was constructed around the ruins of the reactor where it could fit. This bespoke design maximised radioactive containment, but it was never expected to last more than 30 years. A protective 30 km exclusion zone was wrapped around the power plant; this remains in place today.
After the Soviet Union collapsed in 1991, the Ukraine tendered for fresh ideas on how to ensure Chernobyl remained safe for at least a century. Repairing the original sarcophagus was a non-starter. It would have been too hazardous, with levels of radiation expected to reach 100,000 roentgens per hour, twenty times the lethal dose. The French Novarka consortium eventually won the contract. Their proposal was to build a new sarcophagus over the existing one, called the New Safe Confinement. This was to be the largest land-based moveable structure ever built.
It took 10 years to prepare the site; construction began in 2010. The arch-shaped steel structure was shop-fabricated in two halves and assembled off-site. In November 2016 it was transported on purpose built rails and lifted over the old shelter and the No 4 reactor. The following spring, with pre-commissioning and testing activities complete, the NSC was ready.
The NSC spans 257m, is 162 m long and weighs 36,000 tonnes. Designed to last at least 100 years, the structure is extremely resilient to outside elements. It can resist a Richter Scale 6 earthquake, Class 3 tornado, and extreme climates. State-of-the-art ventilation systems maintain the humidity inside below 40% to prevent structural corrosion. Built at an eventual cost of 1.6 billion euros, the NSC completely seals off the damaged power plant from the environment.
As well as sealing in contamination, the NSC will allow the eventual decommissioning of the damaged reactor and old shelter. Remote-controlled robotic cranes wait inside for the day they can tackle this task. There is also the matter of an estimated 200 tonnes of radioactive waste entombed inside which it’s hoped at last can be safely managed.