Chapter 18 Japan, the tsunami and nuclear reactor safety.
“Environmentalists have long been fond of saying that the sun is the only safe nuclear reactor, situated as it is some ninety-three million miles away” Stephanie Mills
It has been about a year since the massive tsunami hit Japan . This disaster had many tragic consequences, one of them being that several nuclear reactors suffered what are called “melt through” conditions. To prevent a complete disaster, several workers were asked to enter the plants despite extremely high radiation levels. I have been thinking about this situation and I think there are some relatively direct approaches to protecting people and preventing dire radiation poisoning in these types of scenarios.
The nuclear reactors involved in the accident are “boiling water” reactors. About 2/3 of the reactor is filled with water. Below the water are uranium nuclear fuel rods. These generate heat which boils the water and creates steam. The steam is directed into a turbine , and this generates electricity. That’s the basic mechanism involved when all is normal.
When the tsunami struck , the Tokyo power company TEPCO lost power , and this result in no electricity. In that situation, there is no cooling of the reactor. Normally there’s a balance between the cooling of the reactor and the heat produced by the nuclear reaction. This balance is disrupted and the water simply boils off completely. The temperature then shoots up to 4000 degrees very quickly, melting off the coating of the rods. After that the radiation leaks through the metal containment- it melts through.
This melt through is actually even more dangerous than a meltdown. It’s inhumane to let this type of situation occur and then send in workers to try and remedy the situation. I think this is a classic situation for having a “dead man’s switch”- a fail safe mechanism that cuts in when a melt through is threatened.
There should be a large ring like container at the top of the reactor that is normally shielded just as the nuclear rods are with a substance like Zirconium. This will ensure that they won’t accidentally trip during normal operation. Inside the container , you have a chemical substance that will coat the bottom of the pill shaped container and act as a buffer to prevent the rods from melting through.
The chemical substance inside the container should be released either automatically at a certain temperature threshold, or manually when an operator decides a melt through is imminent or by a robot to spare having human beings enter the high radiation area. I think suitable candidates for the substance are : ordinary sand, dry cement ,or perhaps glass. Glass will liquefy around 3000 degrees, and it should form an extra coating for the stainless steel bottom.
The idea is that in case of an imminent melt through, the reactors “dead man’s switch” would be tripped and the substance would drop down and coat the bottom. When the rods start melting the substance would be an extra coat and prevent a melt through. I’m certain there is an ideal candidate for this type of substance that a chemist could suggest. This type of safety measure could fairly easily be retrofitted into existing reactors since you can add the ring to the top of the container and just put in some electronic switches for release. The switches should be designed for robotic access so that in a really bad situation you can send in a robot and engage the failsafe mechanism.
I’m sure everyone is familiar with the glass cases that display the message “ In case of emergency, break glass.” My suggested idea could have a message like “ In case of imminent nuclear melt through , break ring”.
Discuss and enjoy!