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Two interesting things to see here, of many. They are really planning the sites to be temporary compared to the solar/wind/ and other industrial power plants th
by hairytrog 6y ago
Two interesting things to see here, of many. They are really planning the sites to be temporary compared to the solar/wind/ and other industrial power plants that have little or no plan for returning their sites to the original virgin soil. And two, they seem to use a molten salt loop like in concentrated solar to meet variable demand without changing the power level of the reactor, which you can't really do because of Xenon poisoning. So it's like a natural gas plant in its ability to deliver power, but clean and holds 20 years of fuel inside the reactor.
- simonebrunozzi 6y ago> which you can't really do because of Xenon poisoning Can you clarify this part? You mean that channging the power level of the reactor would cause Xenon poisoning?
- hairytrog 6y agoI highly recommend HBO's Chernobyl. Explains a lot this stuff. Basically, as a nuclear reactor operates, it is turning the Uranium into lots of other stuff. One component of this other stuff is Xenon-135, which absorbs neutrons and basically gets in the way of nuclear reactions. This is not an issue if you keep the reactor on because there are enough neutrons to keep things going and overcome the Xenon absorption. But if you turn the reactor off, you now have no neutrons from the fission reactions and lots of neutron absorbers. There is so much absorption that it's impossible to start up the reactor for a couple of days. That's why nuclear reactors operate at constant power and only turn off to refuel. This MMR also operates at constant power, which would also have benefits for cycling issues, and uses the molten salt loop to store heat and then use it when it's needed.
- jacobr1 6y agoAh, the the molten salt loop is like a flywheel?
- phamilton 6y agoMy read is that it's somehow the inverse of a flywheel. A flywheel means consistent output for variable input whereas this is consistent input leading to variable output. Or maybe I'm way off.
- Teknoman117 6y agoThat's my understanding as well. Rather than ramping the power output up or down with demand, you keep it at a constant power level and basically use the molten salt loop as a battery -> store energy when you're outputting more than is required, draw energy from it when you need more that you are producing. The multi-gigawatt nuclear installations are typically supplemented by natural gas "peaker" plants to deal with higher demand than the reactor output, but lose any extra power produced. If I recall correctly, the naval reactors (submarine and surface vessels) are the only ones that are designed to rapidly shift their power output.
- littlestymaar 6y ago> The multi-gigawatt nuclear installations are typically supplemented by natural gas "peaker" plants to deal with higher demand than the reactor output, but lose any extra power produced. In France, the load variation is directly handled by the nuclear plants themselves[1], even if there are also some natural gas running (and most of the time their output is more regular than the one of the nuclear plants, so their must be drawbacks to big load variations on a gas plant as well). [1] https://www.rte-france.com/eco2mix https://www.rte-france.com/eco2mix
- Dylan16807 6y agoThat's just one way you can use a flywheel. A flywheel is the equivalent of a battery/capacitor. It can smooth inputs, or it can smooth outputs, or it can simply save power for later.
- PaulHoule 6y agoWhen a reactor is "poisoned" with Xenon, the Xenon absorbs a large fraction of neutrons that otherwise would cause fission. If you don't want to wait for the Xenon to decay you could construct a reactor that has a larger control swing than you would need otherwise -- for instance you could put in more and denser control rods. In that case, however, you need to have a lot of "excess reactivity" and also a lot of neutrons lost in the control rods under normal use, which in turn means the "neutron efficiency" is worse. (If you're not planning to breed Pu239 or U233 maybe you don't care) Note the Xenon concentration can vary in different parts of the reactor so you have to manage the "oscillations" in space just as you do in time. Not a catastrophe, but definitely a hassle.
- drcongo 6y agoThat's an excellent explanation, thanks!
- ncallaway 6y agoScott Manley made a more condensed form of the explanation of the nuclear physics involved here: https://www.youtube.com/watch?v=q3d3rzFTrLg https://www.youtube.com/watch?v=q3d3rzFTrLg (~21 minutes). It's an excellent explanation of the processes. The HBO show is also an excellent drama and worth a watch.
- Dylan16807 6y agoYou can't shut it off on a whim, but lots of reactors can drop to half output or one third output without much trouble. It probably doesn't make a big difference on the current grid, but if you have a significant fraction of nuclear power then the ability becomes useful. (I don't know if those mechanisms are applicable to this design.)
- sbierwagen 6y agohttps://en.wikipedia.org/wiki/Iodine_pit https://en.wikipedia.org/wiki/Iodine_pit
- rtx 6y agoGreat point, power density should be calculated based on land usage.
- ajross 6y agoAnd unlike a natural gas plant, it costs 3-10x what the equivalent generating capacity in renewables would cost. I come to post this Same Thing every time this discussion comes up. It's not about safety. Everyone serious understand nuclear, even current technologies, is "safe enough" to be useful to build out. Nuclear is outrageously expensive, though. And new reactor designs don't seem to be making much progress on that. Look, I think nuclear is fine. But as a numerate and earnest environmentalist, I don't see where the case for it lies. Right now, we should be building out solar and wind as fast as we can, because they're good and safe and CHEAP. And when we get to that last 5-10% where we need buffering capacity that we're currently getting via gas? Yeah, maybe then we can talk about nuclear. But even then... meh. What's the case on trying to finish the job on electrical generation vs. putting those same dollars into low hanging fruit in other areas of the energy puzzle? Nuclear needs to make its case on a balance sheet before it makes sense to talk about.
- Wowfunhappy 6y agoSo, why did so many countries/companies originally build nuclear reactors, if the economics inherently don’t make sense? Has something changed?
- layoutIfNeeded 6y agoYes. Regulations.
- dv_dt 6y agoI think a lot of countries built reactors when the economics of Nuclear reactors as well as the economics of renewables were unknown with respect what they would look like in scaled deployment. Modern looks at the operating costs vs time to build, vs modern construction practices from the US, France, China, et al seems say the economics of Nuclear reactors have stalled or increased, while the economics of renewables continue to make accelerating improvements.
- Baeocystin 6y agoThe economics are what they are do to the legal burden and regulatory overhead more than the technology itself, at least here in the US.
- littlestymaar 6y agoExcuse me, could you be more specific about why you think Xenon poisoning is relevant here? I think I just missed your point.
- necheffa 6y agoXenon is both a fission product and a neutron absorber. So if your reactivity dips too low you won't have enough neutrons buzzing around to sustain the reaction and will have to wait for the xenon to decay before you are able to start up again.
- littlestymaar 6y agoI know very well what is Xenon poisoning, I just fail to see the point they were making.
- jhayward 6y agoIn a situation where you want to rapidly ramp a generator's output up or down, Xenon poisoning narrows the window of reactor control system authority. This prevents the reactor from achieving full power on a reasonable time scale.