There is no real "time" period that it took to clean up, because people have different views about different places.
Some parts of the cities were covered in weeks, while some took months. It took almost a year for the radiation to fully
go away in some areas.
In the US, the cost of cleaning up the radioactive pollution created by the nuclear weapons complex has been estimated
at US $ 365 billion, almost as much as the cost of building a nuclear weapon.