Thirty years ago, the world experienced its worst nuclear disaster at the Chernobyl power plant located in the former Soviet Union, now modern day Ukraine. Chernobyl’s number four reactor suffered a catastrophic power surge on April 26, 1986, triggering a meltdown and explosion that led to the evacuation of the surrounding area. The fallout from the nuclear meltdown exposed millions of people to radiation across Eastern Europe and other parts of the Soviet Union. Experts estimate that the long-term radiation effects will take the lives of at least 9,000 people. “Such catastrophes do not respect state borders,” said Ukrainian President Petro Poroshenko at a memorial event held Tuesday. The concrete sarcophagus that surrounds the reactor — built at the time of the accident and meant to be only temporary — continues to leak radiation to this day. A new steel structure will be built to cover the reactor and prevent further leaking, according to PBS NewsHour science correspondent Miles O’Brien.

nuclear radiation — the energy particles or rays that are given off from a radioactive element, such as uranium, as it decays nuclear reactor —  a device used to generate power, in which nuclear fission takes place as a controlled chain reaction producing heat energy that is generally used to drive turbines and provide electric power