Quickly, and without looking online to find the answers, which of the following is a nuclear meltdown?
Most of them should be pretty easy but there is a good chance I might have tricked you, because the correct answer is none of them. I’ll explain what I mean in a bit, but first I’m going to show you what a nuclear meltdown actually looks like.
But wait, Fukushima was totally a meltdown I hear you say. Yes, yes it was. But that was not what this picture was. This picture is of a hydrogen explosion. And this is a very important distinction that too many people do not realize. Meltdowns are not Explosions.
I get why people have this misconception as everyone always hears about the Chernobyl explosion and Fukushima exploding, but it’s disingenuous and purposefully so. A meltdown that happens in proper containment can no more spread radiation all over the countryside than your bowl of ice cream you forgot about until after it melted could spontaneously coat itself across your entire living room. It needs some external force to contribute to that happening.
Now meltdowns are still fairly dangerous on their own simply due to their temperature. To cause fuel bundles to melt takes several thousand degrees, (melting point of Zr used in bundle cladding is 1855 Celsius) but they can begin to buckle under their own weight as low as 550 Celsius. This can increase the fission rate of the fuel inside as it bends and gets brought closer to other fuel bundles that may also be sagging, which makes more heat, which pushes the reactor further along the path to a meltdown.
But remember, Meltdowns are not Explosions. No matter how hot the fuel gets, the fuel itself cannot and will never explode due to a nuclear reaction. This is due to there not being enough fissile material in a small enough area to create the conditions for a nuclear detonation. Hell even a solid chunk of 95% pure U235 metal the size of your fist can’t make a mushroom cloud without a lot of help. So there is no way that a bunch of 5% U235 oxide is going to have the horsepower to pull that off no matter how hot and bothered you let it get.
The heat of the meltdown might cause a steam explosion if the temperature rises fast enough and it vaporizes enough water fast enough to breach the pressure vessel or other part of the pressure loop like what happened at Chernobyl. Or the temperature might rise slowly but steadily and cause a chemical reaction between the cladding and the water to produce enough hydrogen to become explosive like what happened at Fukushima. I know it sounds like an academic difference at this point but it is very important for people to realize this because once again, Meltdowns are not Explosions! And if people keep conflating the two then we only end up with more needless fear and knee-jerk rejections because people are not getting the information they need to make fully informed decisions.
I keep harping on this because there is an example of a meltdown where no one was hurt, no landscape was contaminated, and all the safety precautions worked. And here’s the thing, it was Before Chernobyl happened and terrified the world. Three Mile Island. A nuclear plant right in the center of the US industrial heartland. Basically the worst possible place for something to go wrong. And what happened? Preparation and safety planning paid off and no one died or even was injured. Which is even more startling when you see what the core looked like after the event.
They call it a partial meltdown but this is still several tonnes of molten zirconium and uranium bearing ceramic that gave their best attempt at becoming a puddle. And yet there was no explosion, no damage to the building and no lasting impact on the surrounding environment or population. This is what proper nuclear safety looks like. Even in the face of the worst possible event, it is contained and mitigated with the loss of nothing but time and money.
Fun fact, lots of research is going in to making next gen nuclear reactors that have liquid fuels rather than the current solid fuels. There are lots of interesting reasons and persuasive arguments for liquid fuel reactors, but the most relevant to this is that you can’t have a meltdown if the fuel is already molten. If the reactor is already built to handle the rigors of containing a hot molten fuel either as a molten salt or a liquid metal then handling a sudden spike in power output is much easier because there is no pesky phase change from solid to liquid that ruins the ability of the core to shed heat.
So next time someone tries to scare you with the dreaded M word and how it would spread radiation and radioactive material all over the countryside remember this simple fact, say it with me now, Meltdowns are not Explosions!