How are the meltdowns at Chernobyl and Three Mile Island similar and how are they different?

In brief, both accidents involve gross failure of a nuclear reactor. The two reactors are of different types, so there are some things that are unique to each plant. Both had the reactor cores damaged catastrophically. And in both cases, radiation was released ourside fuel element cladding and outside containment barriers. What is different is that in the Chernobyl disaster, the atomic pile caught fire. I was built using graphite blocks for moderators. At Three Mile Island (TMI), there was no fire. The radiation released at TMI was some nasty stuff including fission fragments from failed fuel element cladding, but it was released in limited quantities. TMI was an accident. In Russia, things were different. It was a disaster. At Chernobyl, as the core burned, massive clouds of highly radioactive fission byproducts (from the failed fuel elements) were caught up in the fire column and swept aloft with the smoke and heat. This caused the surrounding area to have to be evacuated and some of it was actually abandoned. The small city of Pripyat became a ghost town. This newly constructed community of about 50,000 or so was abandoned. People just walked away. They literally left everything behind and departed with just the clothes on their backs. There were a number of fatalities at Chernobyl, and none at TMI. Some reactor workers and a number of emergency personnel responding to the fire died of radiation sickness. And a number of civilians lost their lives within a few weeks of the accident. One account logged by a helicopter pilot (several choppers dumped water on the fire from aloft) said that in the night, the column of smoke and debris from the fire glowed in the darkness due to the radioactivity. Helicopter pilots were among those who died as a result of their heroic efforts to douse the flames. Links are provided to relevant Wikipedia articles.