Colossal guardian

9 February 2017

As the New Safe Confinement over the Chernobyl nuclear power plant reactor building has been skidded, Sotiris Kanaris looks back at the process of construction and installation and provides an insight into the heavy lifting machinery needed.

The Chernobyl nuclear power plant accident on 26 April 1986 shocked the world and changed the way the nuclear power industry operated. Its impact can still be felt today.

Three decades after the event, the area around the power plant remains abandoned, while the 21-storey Object Shelter built, over the destroyed reactor in October 1986, has eroded due to weather conditions.

In 1997 Ukrainian and international experts developed the Chernobyl Shelter Implementation plan, from which a vast engineering structure known as the New Safe Confinement emerged. The New Safe Confinement has been designed to protect  the environment from radiation exposure for 100 years by enclosing the reactor and protecting the Object Shelter. It also aims to provide a safe workspace for dismantling the reactor in the future.

The 36,200t arch-shaped structure is 108m high and 162m long, and has a span of 257m. Its frame is a huge lattice construction of tubular steel members, supported by two longitudinal concrete beams. Consisting of multiple layers, the cladding is designed to resist moisture and even a class-3 tornado.

In 2007, the contract for the construction of the New Safe Confinement was awarded to the Novarka consortium, comprising French companies Vinci and Bouygues. After site preparation and foundation work, the construction of the gigantic structure began in 2012.

Novarka supplied eight Potain tower cranes and two Manitowoc 2250 crawler cranes. The Potain cranes used in this project were: four MR 605 B, three MD 485 B and one MD 345 B.

In order to carry out a number difficult lifts that required the placement of building materials inside the containment shelter, a Manitowoc 2250 crane was fitted with a 21.3m luffing jib on top of the 61m of main boom. 

Key accounts director at Manitowoc, Jean-Claude Guiter, has been involved with the project at Chernobyl. He says: “Giving the extra reach to the Manitowoc 2250 has boosted its productivity while continuing to ensure the lifting work stays on schedule for this phenomenal project.”

In order to satisfy safety requirements, employees need to complete a training programme and pass strict health checks before working on the jobsite. Additionally, to enter the exclusion zone near reactor number four, workers have to wear a full-body suit and breathing apparatus plus a dosimeter, which measures levels of radiation exposure. The crane cabs in close proximity to the Objects Shelter have been reinforced and fitted with lead protection, which acts as a shield against radiation.

Volker Rodenbeck, supervisor for Manitowoc Crane Care, says: “The erection of the three MD 485 B tower cranes was our biggest challenge as they have been erected near reactor number four. Since levels of radiation increase with height, we had to plan and prepare every stage of the crane assembly in advance.

“We did as much of the assembly work as possible before shipment to the erection area, to minimise the time workers needed to spend in areas of higher radiation. To fit the luffing jib on the Manitowoc 2250 we were able to handle the work between the construction area for the new shelter and reactor number four.”

In December 2016, Dutch heavy lift specialist Mammoet finished skidding the New Safe Confinement. Mammoet skidded the arch from its construction site to the reactor building using a skidding system that has been specially designed for the project. The skidding system is fully remote- controlled and consists of 116 skid shoes with an average capacity of 700t each.

The skid shoes were completely synchronized on both sides of the structure to ensure a smooth and even operation. The tracks of this system were installed in a 33° angle to optimise the load transfer onto the foundations. Mammoet also conducted all the jack up and skidding operations during construction of the arch.

This was ‘a highly challenging task requiring new approaches in engineered heavy lifting and transport,’ the company said. The arch was built in two parts at a ‘special erection area’, a decontaminated area at safe distance from the reactor. Each half of the arch was elevated during three jack-up operations, allowing crews to work at lower heights, increasing cost-effectiveness and improving operational safety.

After the construction of the first half was completed, it was skidded into a special parking zone, clearing the area for the construction of the second part of the arch. Upon completion of the second half the two parts were connected by skidding the first towards the second part.

The New Safe Confinement is expected to be operational by the end of 2017. It will be fitted by robotic cranes systems provided by US-based PaR Systems which will be used to deconstruct the Object Shelter, remove nuclear materials from the reactor core and finally the removal of the reactor and other contaminated structures.

PaR System’s Main Cranes System (MCS) has completed factory testing and has been shipped.

The MCS is 96m long, which is longer than a Boeing 777, and is made up of four major components: two 96m bridges, a classic carriage hoist, a secure carriage hoist, and a mobile tool platform utilising TensileTruss technology. This technology enables a rigid lightweight extendible mobile tool platform, along with a full suite of specialised technologies, for robotic cleanup. TensileTruss technology was also provided by PaR to support the cleanup activities at the Fukushima nuclear site in Japan.

The bridges were built to span the reactor building to ensure the full robotic cleanup. The underhung bridges were designed so that two fully loaded carriages may be on the same bridge at the same time, or driven into a maintenance or storage garage. The classic carriage hoist is used to transport cleanup tools and other materials throughout the cleanup site.

The classic carriage hoist has a lifting capacity of 50t and a vertical lifting distance of 73m. The secure carriage has a lifting capacity of 40t and is used to transport materials, or personnel. The mobile tool platform employs a custom designed TensileTruss that serves as a stable tool delivery platform to support remotely operated high-capacity demolition tools as well as a vacuum and waste container to collect the debris.

The platform is comprised of two triangular platforms with independent wire ropes used to manipulate the lower platform. TensileTruss technology is much more than the standard anti-sway technology used in the crane industry, due to its own inherit structural rigidity. Hoists on the mobile tool platform precisely control the tension of each wire rope, so that the lower platform can handle significant horizontal loads and torques generated by tool usage.

The mobile tool platform can handle 1.5t of side load capacity at an extension of 44m without sway, which would be impossible to achieve with a standard hoist. It allows for remote work to be completed that is remarkable due to the elevation and radioactive environment. The total vertical extension of the mobile tool platform is 70m enabling it to reach from just below the ceiling of the New Safe Confinement all the way to the ground.  

A version of this article was first published in Cranes Today, January 2017. 

Chernobyl Manitowoc towers and crawlers, and Mammoet jacks, at work building the NSC
Chernobyl The outside of the NSC, with Mammoet’s skid system just visible at the base of the structure
Chernobyl Mammoet crew setting up the skidding system to slide the NSC into place
Chernobyl Inside the NSC, working to set up the PaR overhead crane which will be used to dismantle the reactor

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