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Friday, 02 May 2014 12:24cat

New Safe Confinement Arch To Cover Chernobyl Reactor 4

Written by  TheStructuralEngineer.info
The New Safe Confinement Arch will stand for 100 years The New Safe Confinement Arch will stand for 100 years Tim Porter

The Chernobyl nuclear disaster occurred 28 years ago on April 28, 1986. Construction is now underway on the New Safe Confinement shield, a movable structure that will cover Chernobyl’s Reactor 4 to protect the area from radiation. In the past, engineers had not been able to design a permanent way to contain the site’s radiation levels should the aging shelter collapse. The 32,000-ton arch being built will last for 100 years. The final stage of cleanup will begin once the shield is slid into place.

The 300-foot tall steel arch will cost $1.5 billion to build. It is being financed mostly by the United States with 30 other countries also contributing. In addition to the dangerously high radiation levels that force the arch to be constructed near the reactor and then slid into place on Teflon pads, engineers faced many challenges while designing the New Safe Confinement Shield. After the shield is in place, workers will not be able to scrape and repaint the structure.  This normally would lead to the structure rusting and it would eventually fail. The head construction manager for the project points out the while normally steel structures can last for well over a century, they are painted regularly to avoid rust. The Eifel Tower, for example, is painted every 15 years. The arch’s interior and exterior will use rustproof stainless steel but the rest of the arch trusses and bolts will be made from conventional steel. Dehumidifiers will be installed to treat the air that will be circulated around the arch to avoid rust. The first half of the arch also needed to be lifted over 300 feet into place by 10 cable-gripping jacks. The 20 million pound structure is one of the heaviest objects ever lifted.

The arch was also designed to ensure worker safety while it is being constructed. The first half was built in a way that shields workers from the reactor’s high radiation levels even though the arch is being constructed a few hundred yards from the reactor. As a precaution, workers cleared contaminated debris and replaced the top layer of soil at the site to ensure that radiation levels were kept low. Each worker must stay in designated areas while building the arch, and the site’s radiation levels are constantly monitored.

If construction stays on schedule, the arch will be completed by 2017. Once finished, Ukraine will eventually remove the unstable structures in the area and any remaining fuel. This will help to mitigate any chance that radiation eventually reaches groundwater. The final stage of cleanup is expected to last up to a hundred years. The technology to remove the fuel from Unit 4 does not currently exist according to Chernobyl’s radiation specialist. It took over a decade to remove the fuel, by remote control, from other less severe nuclear disaster sites. One possible solution is to let the reactor sit untouched inside the steel arch because the radiation will be contained.

There is concern about Ukraine’s long-term commitment to cleaning up the area. It is not yet clear where the money to start the process will come from. The country’s political turmoil and tension with Russia have only increased people’s fears about Ukraine’s ability to handle the cleanup. For now, though, the project has financing for at least another year.

Sources: NY TimesInhabitat

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