Ukraine suffered the world's worst recorded nuclear accident at Chernobyl. The explosion sent radioactive contaminants out over three continents.
Ukraine shares its borders with seven countries – Romania, Moldova, Hungary, Slovakia, Poland, Belarus and Russia.
Don Wildman: For over half of a century the Soviet Union was a land on the brink of annihilation. From World War II and the Nazi war machine launched the largest military campaign in military history to nearly 50 years of the Cold War, when nuclear holocaust was an everyday threat. For the Soviet Union the only way to survive was to go underground. From a subterranean fort where Soviet troops fended off Hitler's offensive and paid with their lives to a top secret submarine base shown for the first time on American TV and a highly classified, state of the art bunker built to house Soviet dictators and withstand nuclear armageddon.