Using a nuclear blast to seal the well is one such suggestion. The idea is not unheard of. The Soviet Union used the extreme heat of nuclear explosions to seal gas wells with melted rock on at least five occasions between 1966 and 1981.
Engineers have suggested that a nuclear explosion could destroy the wellhead, making the leak impossible to seal. Most importantly, detonating a nuclear device on land to seal a gas well is an entirely different proposition than using one beneath the sea floor to seal an oil well.