This is about Kosmos 954. Kosmos 954 was a Soviet reconnaissance (spy) satellite that was part of the RORSAT (Radar Ocean Reconnaissance Satellite) program. This was a low-earth orbit satellite that used active radar to conduct surveillance on ocean traffic. Kosmos 954 was a pretty useful intelligence-gathering device, which circled the earth every 90 minutes in a 65 degree near-polar orbit, and could penetrate cloud cover to determine ship locations.
Photo of a RORSAT satellite in orbit.
Because Kosmos 954 used active radar, it required a great deal of power - more than a set of solar panels could provide. The power supply was a nuclear reactor with 110lbs of highly enriched U-235 that used liquid potassium/sodium coolant and used thermionic converters to generate large amounts of DC current for the radar system.
A diagram of the small reactor.
Kosmos 954 was launched in Sept 1977, but its orbit had become erratic by December. The Soviets secretly informed the US government that they had lost control of the satellite, and that the system that was intended to place the reactor package into a much higher orbit at the end of the satellite's useful life had failed.
On January 24, 1978, Kosmos 954 entered the earth's atmosphere and fell apart, scattering radioactive debris across western Canada - The Northwest Territory, Alberta, and Saskatchewan. Cleanup began immediately - on the day of the crash. Operation Morning Light started Phase 1, to recover as much radioactive debris as possible before it was buried in snow. This lasted until April, when Phase 2 began. Phase 2 ran through October of 1978, while the ground would be mostly free of snow.
At the end of the cleanup, only 12 larger pieces of the satellite were recovered, and less than 1% of its fuel was recovered. The most radioactive piece recovered was emitting 500 Rem, which would give a lethal dose in 2 hours to anyone nearby.
A recovered chunk of Kosmos 954.
As always, it is interesting to follow up to something that was on the news and learn more details than were available at the time.