Another '60s Nuke Accident

January 21, 1968:

A B-52 bomber crashes near Thule Air Base, contaminating the area after its nuclear payload ruptures. One of the four bombs remains unaccounted for after the cleanup operation is complete.The aircraft was carrying four hydrogen bombs on a Cold War "Chrome Dome" alert mission over Baffin Bay when a cabin fire forced the crew to abandon the aircraft before they could carry out an emergency landing at Thule Air Base. Six crew members ejected safely, but one who did not have an ejection seat was killed while trying to bail out. The bomber crashed onto sea ice in North Star Bay, Greenland, causing the nuclear payload to rupture and disperse, which resulted in widespread radioactive contamination. The United States and Denmark launched an intensive clean-up and recovery operation, but the secondary of one of the nuclear weapons could not be accounted for after the operation completed. USAF Strategic Air Command "Chrome Dome" operations were discontinued immediately after the incident, which highlighted the safety and political risks of the missions. Safety procedures were reviewed and more stable explosives were developed for use in nuclear weapons.
In 1995, a political scandal resulted in Denmark after a report revealed the government had given tacit permission for nuclear weapons to be located in Greenland, in contravention of Denmark's 1957 nuclear-free zone policy. Workers involved in the clean-up program have been campaigning for compensation for radiation-related illnesses they experienced in the years after the incident. In March 2009, Time identified the accident as one of the world's worst nuclear disasters.

Wow, two separate accidents just over 2 years apart.  It is amazing what occurred under Cold War secrecy.