If water stops neutrons completely, then protection designed for ITER will also do so. I have read that neutron embrittlement of reactor walls limits safe operation time of a fission reactor. Reactor contains high pressure hot water (for steam turbine) and all fuel. If it breaks, result is Tsernobyl/Fukushima again. If fusion reactor breaks, small amount of mostly non radioactive hydrogen escapes. I don't know how much fuel fusion reactor has, but it cannot be much. Wendelstein 7-x stellarator used 1 mg of helium in its first plasma test. So both suffer from neutron embrittlement. It is safety issue for fission.
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Breakthrough in Nuclear Fusion
- Thread starter David99
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If water stops neutrons completely, then protection designed for ITER will also do so. I have read that neutron embrittlement of reactor walls limits safe operation time of a fission reactor. Reactor contains high pressure hot water (for steam turbine) and all fuel. If it breaks, result is Tsernobyl/Fukushima again. If fusion reactor breaks, small amount of mostly non radioactive hydrogen escapes. I don't know how much fuel fusion reactor has, but it cannot be much. Wendelstein 7-x stellarator used 1 mg of helium in its first plasma test. So both suffer from neutron embrittlement. It is safety issue for fission.
nwdiver
Well-Known Member
Fusion relies on magnetic containment and high temperatures/pressures to promote fusion. Fission is to some extent the opposite... it needs to 'thermalize' or 'moderate' basically slow down neutrons to maintain a chain reaction. In fission reactors the water isn't simply a shield... it's an active part of the process. Slow neutrons are more likely to cause fission than fast neutrons so the fuel assembly is submerged in water; the water is a very good moderator due to the hydrogen in H2O (the closer something is to the mass of a neutron the better it can slow it down vs simply deflecting it).... you can't submerge a fusion reactor in water and maintain fusion.
To further drive home the point on how difficult it is to get fusion to work vs fission... you don't really need to force U235 to fission... if you can get a neutron to stick to it... U236 is very unstable and doesn't require much additional energy from the neutron to split. It's so easy that for centuries there existed a natural fission reactor in Africa. The physics of what we're attempting with fusion exists no where else in the universe so far as we're aware. The concept of replicating the sun on earth sounds nice until you realize that the power of the sun is mostly a result of its size... the human body actually radiates more energy/kg than the sun.
The point is that while fusion would be awesome and we should certainly pursue it... we are still very very far away from making it work and the odds of it saving us from our fossil fuel addiction are lower than the odds of powerball providing for your retirement. Wind, Solar and storage can and will work... for every $1 we devote to researching fusion ~$10k needs to go into deploying wind, solar and storage.
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These reactions happen a lot during Supernovae explosions. The speed of Sun's fusion power is limited by the lifetime of He2 isotope which is produced by fusion of two H nuclei. It's produced only at high temperatures and it's held together only very weakly, so there's not much time for it to react. In contrast, reactions with deuterium are so easy that pretty much all deuterium burns away immediately.
It's more difficult to ignite He3-based reactions, so the obvious first step is to use much easier D+T reaction. And it's not like we actually _need_ the Moon for He3 - it's produced naturally by decay of tritium.
Another fun fact: we actually already have energy-positive fusion reactors. Japanese JT-60 would have been energy positive if fueled with D+T instead of D+D. And so we're pretty sure that we know how to scale it - it's a complicated task, but not an impossible one.
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No, I'm not confusing anything. The actual usable output of real utility-scale solar power plants is 0.125 MWh per year. I.e. it requires 8 square meters to generate 1MWh of energy per year ( http://www.pnas.org/content/112/20/6277.full.pdf ).
So generating 100000 TWh per year (let's assume that switching to electricity can improve efficiency) will require just 8*10^5 square kilometers of panels. That's a 900x900 kilometer square. And this doesn't even solve the problem of energy storage.
Of course, solar power has some other advantages - it can be used to offset the peak air-conditioning use. And it's OK for residential energy supply.
Actually, without storage, solar can't offset peak AC use since peak consumption occurs in late afternoon/early evening, as opposed to peak solar, which is hours earlier. The problem is that without storage there is zero slack; if the power source is a minute late, it's too late.
Grid scale energy storage seems to me to be near the top of the things we need to deal with.
Actually though, to me, 4th generation nuclear seems the obvious answer, it's just not socially acceptable. Why mess around with something like fusion, that's at best very difficult, when it seems very likely that a minor advance in metallurgy will allow 4th generation fission to solve the energy problem for several centuries. While I'm very doubtful that fusion will be practical within 30 years, I'm pretty sure we can work it out within 300, or we'll have come up with something completely different.
Grid scale energy storage seems to me to be near the top of the things we need to deal with.
Actually though, to me, 4th generation nuclear seems the obvious answer, it's just not socially acceptable. Why mess around with something like fusion, that's at best very difficult, when it seems very likely that a minor advance in metallurgy will allow 4th generation fission to solve the energy problem for several centuries. While I'm very doubtful that fusion will be practical within 30 years, I'm pretty sure we can work it out within 300, or we'll have come up with something completely different.
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nwdiver
Well-Known Member
So here are some real world numbers... my PV array consists of 42 panels and each is 1.7m² for a total of ~72m² and the array produces 17MWh/yr. (17MWh/yr / 72m² = 0.24MWh/m²/yr) That's roughly twice the output of 1MWh/8m²... your statement about a solar plant producing 0.125MWh/yr makes no sense... Did you mean 0.125MWh/m²/yr? Solar farms typically have at least single axis tracking and a more favorable angle than my rooftop array for ~20% more production.
You've got an extra zero in your required energy number unless you're referring to global demand in which case you're 50k TWh shy. US energy consumption is ~10k TWh.. not ~100k.
So let's scale this up to make the numbers more manageable... how much area to generate 10k TWh/yr?
.24MWh/m x 1M = .24TWh/km (There's 1 Million m² in a km²)
10k TWh / .24TWh = 42000 km² or 4.2*10^4 km². That's a 204x204 kilometer square.
Orders of magnitude can be tricky to work with... you either had a typo or a math error :wink:
Even using your number of 0.125MWh/m²/yr generating 10k TWh/yr would only require ~80k km². For perspective there >100k km² of paved surface in the US.
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stopcrazypp
Well-Known Member
Key part of the report he linked where he got the numbers:
"The lowest land use requirements are for NGCC plants, wind, and roof-mounted PV. We consider roof-mounted PV to have zero direct land use because the land is already in use as a building. For ground-mounted solar power, we consider the entire power plant because the modules or mirrors are so tightly spaced that agriculture and other uses are not feasible in the unoccupied areas. Considering only the space physically occupied by the installation, the area requirements decrease by a factor of 2–3 compared with the values in Fig. 1E (8)"
Basically his numbers for land use are higher because they consider the land use for the whole plant (including empty areas). The report however actually counts roof mounted PV as zero impact since that reuses buildings.
nwdiver
Well-Known Member
Right... also if you take out the extra '0' in his energy required number the numbers make more sense :wink:
That's why he's off by a factor of '10'.
I think I figured out what he meant by 0.125MWh/yr and edited my response.
Yes, I assumed some PowerWall-style local storage. Or an equivalent grid storage, just to move the peak by several hours.
I like fission, "nuke'em till they glow, then shoot'em in the dark" is my motto. I have a betalight keychain and I worked at nuclear power plants.
However, let's not kid ourselves - it's not going to be popular.
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Did you count the shaded area? Also, a factor of 2 difference is pretty much nothing for these kinds of estimation.
The world's ENERGY use is 150000 TWh/yr, 15 times more than your estimate.
US EIA ( Elon Musk: How to power the US with solar - Tech Insider ) estimates that we'd need 191817 square miles (700 by 700 kilometers square) to replace the world's energy use with solar. Pretty close to my back-of-the envelope estimation.
nwdiver
Well-Known Member
...yup.... actually that's exactly what I said.... going off the title of your link I assumed it was 'How to power the US with solar'... by bad :wink:
Yes... we would need ~191k sq miles for the world. Pretty sure that globally we can cover that... again... that's less area than what we've covered with asphalt.
Fun Fact... the most abundant element on earth that's a solid at room temperature is also the most important ingredient in a solar panel... it's like it was meant to be :wink:
mangrove79
Member
I was going to start a new thread and post an article on the topic I read yesterday, but found this thread after doing a search. With the last reply being from 2015, it's a good timeline to gauge how far or how short we've come in 6 years.
Bottling the Sun (CNN Interactive, Bottling the sun: The world has been trying to master this limitless clean energy source since the 1930s. We’re now closer than ever)
Some topics covered by this article:
Bottling the Sun (CNN Interactive, Bottling the sun: The world has been trying to master this limitless clean energy source since the 1930s. We’re now closer than ever)
Some topics covered by this article:
- The ITER facility being built in France, a collaboration of 35 countries. It is only a research reactor, not power generation
- The stunning efficiency of fusion - 8 million to 1: 1g of fusion material = 8 tons of oil
- Is fusion truly just 30 years away, finally, given the breakthrough in Feb where 59 megajoules were produced in a 5-sec sustained reaction?
- The abundance of Deuterium and the rarity of Tritium (only 20 kg in the world, didn't know that)
- The complexity of the ITER facility (10 million parts) and delays. The timeline of 2025 for first plasma and 2035 for actual experiments.
- The article ends with this: "This sun, so to speak, will never set.”
Skotty
2014 S P85 | 2023 F-150L
ITER is like the Boeing of Fusion research. Could really use a SpaceX to light a fire under some asses.
mangrove79
Member
I grew up in the 80s and 90s hearing about EVs in the news once every few years, and it's always "this experimental vehicle will change the world someday". Years passed and nothing changed until Tesla came along. Now, EV is a reality and well on its way to replacing ICE even though it'll take many many years. I wish fusion is the next theoretical that becomes day-to-day reality in my lifetime. I've already given up hope on seeing humans achieving multi-planet status, and interstellar travel, but at least give me fusion. LOL.
I dunno that Fusion will ever be a significant amount of energy generation. It's inherently a thermal generator, so other generation sources like solar and wind will always be an order of magnitude cheaper.
nwdiver
Well-Known Member
May your wish be granted
Solar Panels | Tesla
Fun fact about the sun. It radiates ~0.0002w per kg. A human radiates ~6w per kg. So getting a 'sun in a bottle' would actually be incredibly useless. A giant ball ~90M miles away is FAR more useful.
As @miimura pointed out anything that needs to use heat as an intermediate step isn't going to be able to compete commercially with solar and wind for electric generation. I'd much rather see R&D funds poured into a cheap way to get H2 from H2O and convert CO2, H2 and energy into various hydro-carbon fuels. THAT would be game-changing.
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May your wish be granted
Solar Panels | Tesla
Fun fact about the sun. It radiates ~0.0002w per kg. A human radiates ~6w per kg. So getting a 'sun in a bottle' would actually be incredibly useless. A giant ball ~90M miles away is FAR more useful.
As @miimura pointed out anything that needs to use heat as an intermediate step isn't going to be able to compete commercially with solar and wind for electric generation. I'd much rather see R&D funds poured into a cheap way to get H2 from H2O and convert CO2, H2 and energy into various hydro-carbon fuels. THAT would be game-changing.
You really need to be able to do CHP so that the excess heat is useful. So, _if_ you can site the power plant in a way that you can readily use the excess heat the economics improve a bit. Maybe if they put it next to a factory that makes PV...
nwdiver
Well-Known Member
I think the applications where CHP is economically viable are a lot more niche than most people would suspect. The new Ford Class carrier is a good example of this. On the Nimitz class almost everything was steam powered... even the air conditioning was steam powered using adiabatic cooling. On the Ford ~everything is now electric. It's just a YUGE PITA to pipe heat around instead of running some wire. The nuclear facility I worked at had electric heat despite dumping all that process heat into the atmosphere. I always thought it was crazy that we were using electricity to cool the plant AND using electricity to heat our offices....
I’m not exactly sure what point is being made by the comparing radiative power / kg of the sun and a person is?May your wish be granted
Solar Panels | Tesla
Fun fact about the sun. It radiates ~0.0002w per kg. A human radiates ~6w per kg. So getting a 'sun in a bottle' would actually be incredibly useless. A giant ball ~90M miles away is FAR more useful.
As @miimura pointed out anything that needs to use heat as an intermediate step isn't going to be able to compete commercially with solar and wind for electric generation. I'd much rather see R&D funds poured into a cheap way to get H2 from H2O and convert CO2, H2 and energy into various hydro-carbon fuels. THAT would be game-changing.
Why not W/m^2? A person radiates ~ 50W/m^2 while the sun radiates at 5.42x10^16 W/m^2.
ITER if it works would be something like 20 W/kg
Large thermal power plants are expensive so it’s likely that a multi GW fusion power station will likewise be even more expensive compared to the falling prices of renewables.
Grid scale storage is still an issue but the difference in price would allow you to throw a lot of $$ at storage before the costs become equivalent.
However there are enough use cases for dense power production that I’m not willing to write off fusion just yet.
mangrove79
Member
Yep, that part got me confused as well. 99.9999% (and several more 9's) of the sun's mass is not part of the fusion process at any instance, counting them towards this w/kg number is irrelevant at best. And how this strange accounting leads to the "quite useless" conclusion about the exercise of "bottling the sun" is even more puzzling.
The sun uses its enormous mass, therefore gravity, to compress the atoms for fusion. Humans don't have that luxury, so we have to use heat. But that lack of mass is exactly what would make the w/kg number for a fusion reactor much much higher than the sun. All fuel put into a fusion reactor will be used to generate power.
The video was very helpful, though. I didn't know about the difference between Q and Q(plasma). Seems we have a long way to go, but progress is progress. Anyone doubting future possibilities only need to look what humans have achieved in the past.
nwdiver
Well-Known Member
To highlight the difficulty in productively harnessing fusion outside a star as I mentioned upthread.
This fascination with nuclear really confounds me. Is not the objective cheap, abundant and reliable energy? Nothing is cheaper or more abundant than wind and solar. If we could use that to manufacture hydrocarbons like propane would that not also make it just as reliable?
mangrove79
Member
Maybe because the stars aren't powered by wind and solar themselves? j/k. I don't know if it's really a fascination, at least for me it isn't, but rather "common sense" based on what I've read and heard. admittedly I'm probably ignorant on this topic compared to you. Wind and solar have always seemed to exist in that fringe space in a supporting role for many years, and there hasn't been any breakthrough technology on those fronts as far as I've heard. You still have those giant turbines on hills and coastlines, you still need tons and tons of space for solar panels. On the other side, fusion reactors aren't weather-dependent, have abundant fuel sources, small footprint, and can be closely located to power centers. They don't have any of the drawbacks of fission reactors. Assuming humans can keep making technological breakthroughs on magnets and efficiency, and can lower the cost, fusion seems to be the holy grail or clean sustainable power.
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