The 25th anniversary of the Chernobyl nuclear disaster is next month. On April 26, 1986, a series of explosions destroyed Chernobyl's reactor No. 4 station and several hundred staff and firefighters tackled a blaze that burned for 10 days and sent a plume of radiation around the world in the worst-ever civil nuclear disaster. More than 50 reactor and emergency workers were killed at the time. Assessing the larger impact on human health remains a difficult task, with estimates of related deaths from cancer ranging from 4,000 to over 200,000. The government of Ukraine indicated early this year that it will lift restrictions on tourism around the Chernobyl nuclear power plant, formally opening the scene to visitors. It's expected, meanwhile, that a 20,000-ton steel case called the New Safe Confinement (NSC), designed as a permanent containment structure for the whole plant, will be completed in 2013.