 Complete the following phrase:  Meanwhile, the laboratory was also helping to design the reactor for the worlds first nuclear-powered submarine, the U.S.S. Nautilus, which steamed for more than 513,550 nautical miles 951,090 km. The next nuclear reactor model was Experimental Boiling Water Reactor, the forerunner of many modern nuclear plants, and Experimental Breeder Reactor II EBR-II, which was sodium-cooled, and included a fuel recycling facility. EBR-II was later modified to test other reactor designs, including a fast-neutron reactor and, in 1982, the Integral Fast Reactor concepta revolutionary design that reprocessed its own fuel, reduced its atomic waste and withstood safety tests of the same failures that triggered the 