BUILDING AN ARCH

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Today, a New Safe Confinement(NSC) is being constructed atChernobyl. It is an arch-shapedstructure which will be placedover the destroyed unit to providea controlled, weatherproof envi-ronment. The objective of theNSC is to confine the solidradioactive remains of Unit 4 forthe next 100 years and to allow apartial deconstruction of the oldplant in the future.

The project is led by Novarka, ajoint venture between Frenchcompanies Bouygues TravauxPublics and Vinci ConstructionGrands Projets. Mammoet wasselected by Novarka to engineerand execute the jack-up and skid-ding operations –a highly chal-lenging task requiring newapproaches in engineered heavylifting and transport.

The arch-shaped confinementstructure is a design and con-struction project that is quiteunique in the history of engineer-ing. The structure will ultimately

rise to a height of nearly 110meters, will be close to 165meters long, have a span of about260 meters and weigh close to35,000 tons. That is big enough tohouse the Statue of Liberty orParis’ Notre Dame Cathedral.

The arch is being constructed ina decontaminated area – the ‘spe-cial erection area’ – at a safe dis-tance from the reactor. It is builtin two equal parts. Each half iselevated during three jack-upoperations. The first half of thearch has already been finished.It was raised to its full height in2013 and skidded to a temporarylocation, or ‘waiting area’, clear-ing the special erection area forconstruction of the second half.Building the arch in two parts ismore cost-effective, as it requiresonly half the jacking capacitywhen compared to elevating theentire arch in one go. Cost-effec-tiveness is further increased byelevating each part in three jack-ing operations as it allows con-struction at lower heights. This

would not be entirely possible ifeach arch would be elevated inone go.

To tackle the challenges posed byboth the jacking and skiddingoperations, Mammoet designedan integrated approach covering arange of innovative, specializedsolutions.

A customized jacking system wasdeveloped by Mammoet: thestrand jacks are housed in specialcontainers which are placed ontop of the tower sections, makingit easy to remove the strand jacksfrom the tower sections and lowerthem to ground level for mainte-nance. This allows for efficientmaintenance of the jacking unitswhile the towers are being relo-cated. New software was alsodeveloped to ensure precise con-trol of as much as 60 strand jacksworking simultaneously. A newcamera system, with a camera inevery container, monitors thereels and strand jacks from thecontrol room. In addition, a cus-tomized method of protecting thestrand wires against the extremeweather conditions is applied toreduce the risk of having to renewit regularly.

The most significant innovationfor this project is the tailor-madeskidding system. It has been engi-

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Special erectionarea: dedicated areafor constructionactivities.

A Waiting area:temporary locationfor arch 1.

B Reactor Unit 4: areato be confined.

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Site overview

Skidding arch 1 from the special erection area(A) to the waiting area (B) using a custom-builtskid system. The second arch is erected usingthe same method as the first arch.

1 Skidding first arch back to be connectedwith second arch in the special erectionarea and then skidded over Reactor Unit 4.

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Those of us old enough will remember the accident at theChernobyl Nuclear Power Plant in Ukraine, in April, 1986. This

accident partly destroyed Reactor Unit 4. Shortly after the accidenta shelter –often referred to as ‘the sarcophagus’ –was constructed,as an emergency measure to contain the radioactive materialswithin this unit. As this sarcophagus was built under extreme conditions and with great haste, it was clear that a more sustainablesolution would be needed eventually.

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Arch 1 is fully elevated andready to be skidded fromthe special erection area (A)to the waiting area (B).

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Arch elements added andthird jack-up to elevate thearch to its final position.

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Repositioning jackingsystem for third jack-up.

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Arch elements added andsecond jack-up operationto elevate the arch further.

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Repositioning jackingsystem for second jack-up.

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First jack-up to elevatethe arch.

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Each arch is elevated in three jack-upoperations at the special erection area

neered to position the arch sec-tions. The system is fully remotecontrolled and has 116 skidshoes, with an average capacityof 703 tons each. It has beendesigned to operate completelysynchronized on both sides ofthe structure, to ensure the archmoves evenly during the skid-ding operation.

Once the second half of thestructure is finished, the twohalves will be connected to formthe complete arch that is to beplaced over the Reactor Unit 4of the Chernobyl nuclear powerplant. In order to connect thetwo sections, Mammoet will skidthe first part back towards thesecond part. The skidding oper-ation is scheduled for late 2014or early 2015, after which it willtake a year to install a fullyremotely controlled overheadcrane system and various moni-toring and control systemswhich will ensure the integrity ofthe structure for its designed lifespan of a minimum of 100 years.

Upon finishing all preparatoryworks, the complete arch,weighing approx. 35,000 tons,will be skidded over a distanceof 330 meters to Reactor Unit 4in approximately 1 week, com ple ting this exceptional project. n

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