The world’s largest moving land structure now covers the site of the world’s worst nuclear accident. In December 2017 engineers pushed a vast 36,000 tonne steel tomb over the highly radioactive remains of Chernobyl reactor 4 in Ukraine, safely confining it for 100 years
In 1986 an explosion destroyed the 1 GW graphite-moderated unit 4 reactor at Chernobyl nuclear power plant, releasing at least 5% of its reactor core into the atmosphere. Radioactive contamination spread for several hundred kilometres around the site.
Up to 400,000 people were evacuated from a 26,000km2 exclusion zone which is still in place. Over 30 site workers and firemen died within weeks of the accident and thousands more have died or are expected to die from cancer directly caused by the radiation.
The reactor remains were buried within six months under a hastily built steel and concrete sarcophagus. However, as described in the ICE's Civil Engineering journal 10 years later this soon became dangerously unstable (Smith and Larcombe, 1997).
A new tomb
A new tomb was clearly needed, but it had to be big enough and strong enough to allow safe demolition of both the now radioactive sarcophagus and the still very dangerous remains of the reactor.
The 270m wide, 162m long, 108m high steel arch structure was constructed 180m away from unit 4 and jacked into position on PTFE-lined tracks – making it the largest-ever structure to move on land.
The contract was awarded in 2007 to Novarka, a joint venture of Vinci Construction Grands Projets and Bouygues Travaux Publics. The €2.1 billion project has been funded by contributions from more than 40 countries, the European Commission and the European Bank for Reconstruction and Development.
The full story of the design and construction of the so-called 'new safe confinement' (NSC) is told in the latest issue of Civil Engineering (Maltini and Asamov, 2017).
According to lead author Fulcieri Maltini, who was responsible for the decommissioning programme between 1994 and 1997, 'The decommissioning of Chernobyl unit 4 is one of the world's largest and most complex engineering works. Following more than 10 years of work to build several structures to improve the safety of the site, a more secure and controlled area will finally be established in the near future.
'The completion of the NSC and its sliding into its final position will prevent the intrusion of water and snow and protect the environment from the release of contaminated dust. The NSC will be equipped with cranes and remotely controlled process equipment for dismantling and strengthening the unstable building structures and the retrieval of fuel-containing materials from the sarcophagus shelter. The NSC has been designed and built for a working life of more than 100 years.'
In addition to the new safe confinement, the paper reports on progress with the design and construction of a new interim spent fuel storage facility, liquid and solid radioactive waste treatment plants and a solid waste storage complex. All have been designed for a 100 year life.
The decommissioning and dismantling of units 1, 2 and 3 is already under way and planned to be completed by 2064. However, Maltini says complete decontamination, 'will be solved only in the very distant future due to the significant amount of radioactive substances concentrated both on the Chernobyl site and within the exclusion zone area.'
He concludes, 'The decommissioning of Chernobyl will remain in the history as one of the major engineering accomplishments and a demonstration of the immense potential danger of nuclear energy.'
For further information please contact the ICE Proceedings editor Simon Fullalove at [email protected] or on +44 (0)20 7665 2448.