The Chernobyl liquidators were responsible for walking on the roof or reactor number four to remove radioactive debris. This debris included fuel rod particles and radioactive graphite control rods. The roof was so radioactive that more than 10 minutes on the roof would have been a lethal dose. these men had to wear lead suits weighing 30 kilograms and could only work from 30 seconds to 5 minutes on the roof.
If you look closely you can see the effect or radiation on the photographs. The white streaks are where film has been exposed to radiation.