SmokeyBloke
After WW2, and the bombing of Hiroshima, America did not discard Radioactive technology. Instead, they used it to make amazing technology, such as energy weapons and robots. They were at a horrible war with China, and a strange company known as Vault-Tec constructed 317 vaults across the country. What they did not tell America was that they were all secret experiments. One vaults door was set not to fully seal, another put everybody into cryogenic sleep. When China dropped the nuclear missiles on America, people ran into the vaults. There were not enough, and many who didn't make it were mutated into horrible creatures.
One vault in Boston, 218, was told to send 3 people ranging from 15-18 out into the Commonwealth, the name of the radiated land in Massachusetts. If it did not comply, all the residents in the vault would apparently die.