Q: Would dumping anti-matter into the Chernobyl reactor when it was melting down stop the meltdown?
Randall’s response: “A. J. [submitter], in recognition of your Chernobyl response efforts, we award you the ‘For God’s Sake, What Were You Thinking?!’ Award. It’s shaped like a VHS tape of the Star Wars Holiday Special.”
My response: No. No. Oh God, no.
I’m going to assume that this idea was inspired by the practice of putting out oil well fires with dynamite, since that makes more sense than anything else I can think of.
Dynamite does not put out the fire by using up all of the oxygen in the air. Being an explosive, it already has all the oxygen it needs in its chemical structure. Instead, force of the explosion blasts all of the ambient oxygen away from the fuel source (the oil well). It’s basically the same principle as blowing out a candle, except on a massive scale.
The fire and explosion at Chernobyl were a complicated event. Basically, a combination of design flaws and human error during, ironically, a safety test caused the reactor to overheat, producing more than ten times its normal power output. This boiled the water coolant, causing a steam explosion, a possible fizzled nuclear explosion, followed by a graphite fire once the destroyed reactor was exposed to the air. It was the graphite fire that blew most of the fallout into the air.
The question is whether antimatter would have stopped the reactor from overheating in the first place. The details of how it happened are not all that important because the answer is a resounding no!
It’s fairly well-known that the more powerful hydrogen bombs, which use nuclear fusion, use atomic bombs (which use fission) to trigger them, because it takes too much energy to start nuclear fusion any other way. What is less well-known is that a type of bomb called a boosted fission weapon uses a small fusion explosion to trigger an additional, larger fission explosion.
When antimatter reacts with matter it produces a nuclear fireball, similar to a hydrogen bomb. This fireball is made of high-energy particles like pions and kaons instead of neutrons, but its effects are similar. The high-engery pions and kaons are easily energetic enough to split any atomic nucleus they hit—not just uranium from the reactor, but also the lead shielding and any other heavy metals in the structure.
Normally, nuclear reactors cannot blow up in a nuclear explosion because the fuel is not weapons grade. The radioisotopes are not pure enough to sustain an explosive reaction. But the pions and kaons will also split those other isotopes, and you would get a nuclear explosion, just like in a boosted fission weapon.
In other words, dumping antimatter into a nuclear reactor that is melting down is just about the only thing that could turn it into an atomic bomb. Congratulations, you just made Chernobyl a thousand times deadlier.