Regarding looking for deep geothermal pockets, you forget a detail: besides the difficulties related to drilling, it is still necessary that the water manages to stay hot time to reach the surface ... A pipe of several kilometers that make a sacred radiator!
Grelinette wrote:the "minimal benefits" that we derive from it, namely, to heat water only a few hundred degrees, if I may say so!
By the way, do you know what temperature from a nuclear reaction is actually used to heat the water that will drive the turbines at the end of the process to produce electricity?There are some values on the internet,
of the order of 300 to 400 degrees in the primary circuit, ie the circuit whose water will directly recover the heat produced by the nuclear reaction, (
See the EDF website) ...
while the nuclear reaction is capable of producing some 15 000 000 of degrees Celsius. (We "play" with fifteen million degrees to use 300!
).
The water is heated to about 330 ° C.
It circulates in closed circuit between the reactor and the exchangers (steam generators). In the exchangers it cools to about 290 ° (if my memory is good), then goes back into the reactor.
The entire circuit is maintained under a pressure of 3 bars so that the water remains in the liquid state.
You speak of nuclear fission as a flame of which one would only use a small part of the heat; this is not the way to see things.
A flame needs a minimum temperature to be serviced. Nuclear fission occurs regardless of the temperature.
If the fuel is completely isolated, the temperature can rise to extreme levels because the energy produced remains in place. That's what happens in a bomb.
If we take this energy, we prevent the rise in temperature. This is what happens in a power plant.
The temperature is stable when the power taken is equal to the power produced by the reaction.
In a power plant, the power drawn is related to the demand of the network, it is a deposit. It is therefore necessary to adapt the power of the nuclear reaction continuously so that the temperature of the circuit remains stable.
The power of the reaction is controlled by the absorption of neutrons, using boron diluted in the water of the primary circuit and graphite bars between the fuel elements. The more neutrons are absorbed, the less is left to sustain the reaction.
When we absorb more neutrons than the reaction produces, it slows down (we say that it converges).
When the reaction produces more neutrons than we absorb, it accelerates (we say it diverges). In this situation, you have to react quickly or you will see the reaction run out of steam.
It is for this reason that there is a slow control means (concentration of boron in water) and a means of rapid regulation (depression of the graphite bars in the reactor).
Precision in passing: we could control the reaction only with the graphite bars, the problem is that they cause an irregular wear of the fuel elements (those of the top are almost always surrounded by the bars, they do not wear out almost , while the bottom ones are almost never except when the reactor is stopped). So they choose rather to regulate the average power thanks to the amount of boron and to move the bars of graphite only for the short term variations.
I reassure you, the disposition of the elements of uranium in the reactor makes that a runaway is not possible: even if the reaction diverges strongly, one will be always able to absorb more neutrons than it can produce some.
Where it becomes annoying is when you do not cool down enough and the reactor starts to melt. Because suddenly we end up with large piles of molten uranium that are no longer crossed by boron water or graphite. There is a risk of not being able to regulate the reaction: it diverges freely and it is the catastrophe (Fukushima, Chernobyl).
The amount of fuel to be collected in a compact manner so that the reaction diverges without possible control is called critical mass. It depends on the type of fuel (for uranium 235 for example it is 48 kg).
Several small stable blocks that are suddenly crushed against each other (using a detonation for example) thus achieve this critical mass. This is how we light a bomb A.
Well I'm a little scattered, but all that is to say that there is no waste in a reactor:
- the water is certainly not heated very strong but its flow is enormous, the power of the boiler is high
-The reaction is controlled and therefore slowed down, but suddenly it can last longer (exactly like a battery): all the available energy is therefore well and truly used in the end
(Well, that's not quite right, because we replace the fuel well before it has become completely inactive, of course)
A note on performance:
A pressurized water reactor of the P4 type (for example) produces a thermal power of 4500 MW. The output electrical power is 1300 MW. The rest is divided into thermodynamic losses (turbine efficiency), heat losses (pipe insulation) and consumption of the power plant itself (pumps, easements etc.)
