Two specially constructed tanks were used. The first one, based on the abandoned plant's primary reactor containment vessel, held of water, was 55 feet (18 m) deep and 209 feet (70 m) across. At the time, it was the largest fresh-water filtered tank in the world. Additional scenes were shot in the second tank, an unused turbine pit, which held of water. As the production crew rushed to finish painting the main tank, millions of gallons of water poured in and took five days to fill. The Deepcore rig was anchored to a 90-ton concrete column at the bottom of the large tank. It consisted of six partial and complete modules that took over half a year to plan and build from scratch.