CHERNOBYL, UKRAINE — As nuclear workers in Japan struggle to contain radiation from the Fukushima reactor, world attention is turning back to Chernobyl, Ukraine. There, people prepare to mark the 25th anniversary of the explosion that blew the roof off Reactor Number 4.

Soviet planners designed Chernobyl in the 1960s to become the largest nuclear power station in Europe.

Instead, Chernobyl is remembered today as the site of the largest nuclear disaster in the world.

Late on the night of April 25, 1985, Yuri Andreyev left his shift as an engineer at Nuclear Reactor No. 4. Ninety minutes later, a safety experiment went awry. The fuel rods melted down, an explosion blew the roof off, and a raspberry-colored light spewed into the night sky.

When Andreyev returned to work, he saw a scene of devastation. After stepping over the discarded boots, jacket and helmets of fire fighters, he stood in the ruined computer control room and looking up saw blue sky.

Twenty-five years later, Andreyev runs Chernobyl Forum, a political lobby for Ukraine’s 100,000 surviving ‘liquidators’ or clean-up men and women. After weeks of heroic work, the liquidators had succeeded in sealing the plant in an improvised steel and cement ‘sarcophagus.’

But that was not before […]