Who else here knows a little about these things?
I think they push these reactors to the point of being too dangerous.
A reaction takes place when you have a significant amount of this nuclear material close to ANOTHER significant amount.
That’s it.
They just put fuel rods next to each other and they heat up.
The temperature is kept in balance by coolant that then gets super-heated and generates steam in water in a different set of pipes, and this steam is used to run good old-fashioned steam turbines (electric generators)
The two sets of fuel rod water and steam generating water are never mixed.
(I am calling it ‘water’ for simplicity)
A ‘meltdown’ occurs when the fuel rods are so close to each other for too long that they heat up too much and begin to melt. Once they melt, they can actually melt into a pile of material that all by itself has enough critical mass to generate more reactions and heat up more and more.
This can theoretically melt through the bottoms of the reactor core, and down through the earth (to “china” - therefore the name “China Syndrome” from that idiotic movie)
In an emergency they ‘scramble’ which simply means drop down the one set of fuel rods to separate them and stop the critical reaction, and flood the coolant)
It would seem to me that simple gravity and a push button would drop one set of rods away from the other.
So.. to my original question. Is this ‘critical mass’ point so close to the catastrophic melting point that it can happen too fast for the separation to occur?
why don’t they just operate these things a little LESS efficiently, but far more safely? (i.e. NEVER put two masses so close that they can ever melt)
I know the closer together they are, the more heat generated- but the cost of a meltdown is far more than the electricity generated.
Fukishima would have gone down in history as a stunning success- if not for a lack of... BATTERIES to back it up.
They should have had at the very top of their list backup batteries and a helicopter to go get some.
In China, they call the “China Syndrome”, the “American Syndrome”.
Do you actually believe people that get degrees in nuclear engineering are not smart enough to understand basics and safety?
You grossly over simplify and then criticize those that do the actual work.
It was not a lack of batteries that caused the Fukushima Daiichi nuclear disaster.
Respectfully, your response is riddled with errors.
First, there’s a lot more to reactor design than “just putting fuel rods next to each other and they heat up.” The fuel rods are inserted into fuel assemblies which contain somewhere between about 60 and about 200 individual fuel rods. The fuel assemblies are then inserted into the reactor when it is shutdown (the Canadian CANDU reactor can be refueled while producing power). A reactor core will contain between about 120 to more than 800 fuel assemblies.
Postulated accident scenarios are analyzed prior to insertion of the fuel assemblies.
The temperature is not kept in balance by a super-heated coolant. In a pressurized water reactor (such as is being constructed in China, South Carolina, and Georgia), the water is pressurized to 2250 psi and is kept in a liquid state. The heat in the coolant is transferred, as you write, to water in a separate circuit at lower pressure where it does boil to steam which then powers the turbine-generator.
In a boiling water reactor (such as that used at Fukashima), the system is pressurized to about 1000 psi and the coolant boils at saturation temperature in the core and goes directly to the turbine-generator.
A meltdown does not occur when the fuel rods are so close together for too long. The fuel rods are fastened in the fuel assemblies and do not move. A meltdown occurs when the coolant is lost. The reactor is already shutdown, and the fission chain reaction has been shutdown.
While recriticality can in principle occur if a core melts, I don’t think that we have actually seen one.
In an emergency, the reactor is “scrammed”, which means that the control rods are inserted. No fuel rods are dropped. I have no idea what “flood the coolant” means? If certain sets of instrumentation responses are received, then a “safety injection” is triggered in which the reactor vessel is flooded with additional coolant due the instrumentation response indicating that the coolant system has a leak.
A reactor scram can be automatic or can be manually actuated. If it is a manual scram, then you are correct - a button (large red) is pushed and the control rods (in a pressurized water reactor) dropped in due to gravity. (The control rods are inserted from the bottom of the core in a boiling water reactor and are hydraulically driven).
Your final question is based on a misunderstanding of how a reactor operates.
When the uranium or plutonium fissions, it typically splits into two isotopes, both of which are radioactive. Their radioactive decay produces heat, which must be removed. When a reactor is shutdown, the fission chain reaction is immediately stopped, but this decay heat contiunes - when the reactor shuts down, the decay heat is about 7% of the power immediately before the shutdown. The amount of decay heat decreases with time. A meltdown occurs when this decay heat cannot be removed.