Most likely the US would only use small nuclear bunkerbusters to...

Most likely the US would only use small nuclear bunkerbusters to penetrate deep underground proccessing facilities that conventional bunkerbusters could not penetrate. Fallout could occur from dirty bomb effect produced by the escape of small amounts of radioactive material held within the facilities, if not completely burried by the blast, but this is unlikely. Nuclear or conventional bunkerbusters will make little difference, the risk would be the same. Result, higher petrol prices.