In order to vaporize something you need a huge amount of energy , a nuclear bomb has this energy capacity so it vaporizes itself and stuff around it upon explosion , a nuclear reactor core doesn't have such a level of enrichment nor critical mass to achieve these conditions.
The blast at Chernobyl was huge no doubt , thick reinforced concrete walls and structures collapsed.
To me it seems most of what got out was either solid objects (fuel pellets, control rods, graphite core elements , some piping and everything else that got along the blast shockwave) then everything else was mostly smoke from the fire and dust.
Take for example the 9/11 when the twin towers fell there were large dust clouds created , also whenever a building falls even small few story ones much dust goes up, would you also say that the building vaporized itself? Or can we simply conclude that dry cement (the wtc towers had thin cement floor slabs to finish off each floors surface area) creates dust even when simply being drilled or scratched with a sandpaper not to mention total destruction upon a complete vertical collapse.All in all I doubt the core vaporized itself , it exploded yes maybe some tiny bits got vaporized but then after the explosion it lost it's critical mass and all that happened from then was a rather slow melting of the leftover steel and concrete due to a heat source creating huge temperatures.
Although I think it's hard to say the exact amounts of C14 or other releases simply because at the moment nobody really gave much attention to it as everyone was too busy trying to contain as much as they can and save what can be saved.Also I don't get why you talk so much about core vaporization , any radioactivity release is just as bad , what would it matter , the smoke too contain particles as dust etc.P.S. Since you posted while I was writing , well you are right , since i was in such a unit myself I can say there really isn't anything that can burn with such a flame , everything is either metal or reinforced concrete.
I'm not an expert I don't know whether graphite can burn so much , maybe it can if it's surrounded by a large heat source that happens to be radioactive at the same time.
The few people who saw it that night also described bright flames and sparks shooting out.
Well maybe check out the "Windscale accident" which happened in 1957 in UK. They too had a graphite core reactor, a very simple design , it's only purpose was plutonium production.They too had the core "on fire" because some fuel rods overheated and melted themselves although If I recall the core itself didin;t catch fire.Well the total power also wasn't so high but well who knows.
I don't want to dismiss the eyewitness account but remember also that eyewitness account is the most contradictionary evidence there is especially when the eyewitness himself has gone through something as severe and traumatizing both mentally and physically as a nuclear reactor explosion when you are it's operating crew.
the firefighters also said back then that they picked up the glowing graphite and fuel elements ejected and throw them to one another because they didin't know what it was but they were attracted to it because of it's strange glow, now after 30 years those who survived which are few , tell a different story , they now say they actually knew that it was half molten uranium rods they were holding in their hands.
Now which case you believe more? From my experience and knowledge I definitely can say that they knew nothing of how dangerous the things were that night nor that they handpicked live uranium for fun, because if they would have known they would have never went anywhere near that place.
So much for eyewitness accounts.
Now, some numbers.