On April 26, 1986, disaster struck the Chernobyl Nuclear Power Plant in Ukraine. The accident took the lives of 31 people that day, though the total number of people whose deaths can or will be directly attributed to the radiation is unknown, as estimates are widely varied. The area was evacuated and still to this day the Chernobyl Exclusion Zone covers 2,600 km2 (1,000 sq mi) where humans are only allowed to enter with written permission. Though humans are unlikely to re-inhabit this land, wildlife has surged.
While radiation has certainly caused mutations in some of these animals, it is astounding that the area has been able to come back as much as it has. However, human poachers are still proving to be a problem.
Check out this documentary called Radioactive Wolves that gives more details about the biodiversity in the Chernobyl Exclusion Zone: