Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

US Department of Energy: Fusion Ignition Achieved

energy.gov

Post reply on HN
Print view View original

791–800 of 1001 posts

Re: US Department of Energy: Fusion Ignition Achieved

#791

Post by wizofaus »

twic wrote: post #429
subsubzero wrote: post #372

Earlier quoted context omitted.

Do we know how much tritium is needed for a city's energy generation? What about a state etc? Reason I ask is the only uses I have seen for tritium is on old watch dials made in the pre-90's. Curious how much of this resource is out there.

Take spullara's numbers: 2.01410177811 u = 3.34449439340696e-24 g deuterium 3.01604928 u = 5.008267217094e-24 g tritium 17.6 MeV = 7.832863e-19 kWh energy Divide through, and you will see that you need 4.27 ug/kWh of deuterium, and 6.39 ug/kWh of tritium. A random source [1] says that New York will use 50.6 TWh per year by 2027. That would require ~216 kg/yr of deuterium and ~323/yr kg of tritium. This is all assumin…

That such a small amount of matter could generate so much power is pretty remarkable. I might be way off base but from what I can find online it seems you'd need over 2000 times as much uranium?

Re: US Department of Energy: Fusion Ignition Achieved

#792

Post by moloch-hai »

eropple wrote: post #620
SiVal wrote: post #612

Earlier quoted context omitted.

Iron is always spoken of as the dividing line, but I'd like to know whether iron is exactly on the line, on one side (which?), or it depends. IOW, does fusion of iron atoms release energy (hydrogen side of the line), absorb energy (uranium side of the line), neither, or either (depending on conditions)?

As I understand it, iron is the first element that absorbs energy under fusion, and therefore won't fuse further. Could be wrong, though.

It will happily fuse further. It just won't support the outside of a star against gravity, while doing it. So the star collapses, fuses lots more stuff even heavier than iron, and then explodes. Most of the iron and heavier stuff fuses into the core of a neutron star, the ultimate in energy-consuming fusion.

Re: US Department of Energy: Fusion Ignition Achieved

#793

Post by eru »

floxy wrote: post #686
w0mbat wrote: post #577

Earlier quoted context omitted.

Their total power draw from the grid was 300 megajoules and they got back about 3 megajoules, so don't start celebrating yet. Source: New York Times.

I guess we should take this as a lesson in communications. The "breakeven" thing is a red-herring that should have been have been left out of the message, or at least only mentioned as a footnote. The critical ELI5 message that should have been presented is that they used a laser to create some tiny amount of fusion. But we have been able to do that for a while now. The important thing is that they were then able to…

> [...], or the ginormous fusion of the sun.

The sun actually has very little fusion per cubic metre or per kg.

Per volume the core of the sun produces only a quarter of the heat of the human body (and per kg it's even less, owing to high density).

That's why our fusion reactors can't just mimic stars, they have to far surpass them to be useful to us.

Re: US Department of Energy: Fusion Ignition Achieved

#794

Post by eru »

tuatoru wrote: post #742
hackbinary wrote: post #679

Earlier quoted context omitted.

300 MJ is about 83 KWh. In the UK is 1 KWh is £0.34 So, this costs £28 in electricity to run this experiment. The experiment is a momentary thing. Clearly there is now some work to, but now this is becoming an engineering problem of how to extend, sustain, and scale this process.

To have a hope of supplying grid power, they need to scale up the energy gain by four orders of magnitude and reactor run time by 12 orders of magnitude. Those are just two of the engineering problems. It'll be a while, and I doubt it will ever compete with solar, wind, and storage.

> [...], and I doubt it will ever compete with solar, wind, and storage.

Maybe not on earth, but there are applications in deep space.

Re: US Department of Energy: Fusion Ignition Achieved

#795

Post by eru »

bmmayer1 wrote: post #103
jkelleyrtp wrote: post #33

> LLNL’s experiment surpassed the fusion threshold by delivering 2.05 megajoules (MJ) of energy to the target, resulting in 3.15 MJ of fusion energy output, demonstrating for the first time a most fundamental science basis for inertial fusion energy (IFE) Yesterday, everyone was complaining about the 2.2:2.0 ratio, but now we're working with 3.15:2.05. With modern lasers, that'd be a total Q of 0.375 assuming 100% ef…

This is a stupid question but I don't know anything about fusion: How is it possible for X energy to create X+Y energy in output? Doesn't that violate some fundamental law of physics?

The analogy is that settings a pile of wood on fire requires a small amount of fire to start a big fire.

Energy in total is still conserved, but it makes engineering sense to compare the size of the starting fire to the total inferno created.

Re: US Department of Energy: Fusion Ignition Achieved

#796

Post by vlovich123 »

opportune wrote: post #699
vlovich123 wrote: post #652

Earlier quoted context omitted.

I think you're hand waving too many of the problems away and letting your imagination run way ahead of reality. > no need for fission plants Not sure why this is a goal in and of itself. Everything you said is available today with fission and yet still too expensive to remove CO2. Fission has a more real shot at getting to the right price point before fusion even gets off the ground so why not push for more arrows be…

Energy is an input to basically every single thing we make or do. In economic models it’s often been found that “technology” parameters (inversely) correlate almost entirely to energy prices. If energy cost very little, we could do previously unviable things like vertically farm and let farmland go back to nature, smelt ore onsite, or run simulations/models for a fraction of what they cost now.

That’s what I’m saying. Why are you assuming that energy costs for fusion would suddenly be lower? These plants take a lot to build and it’s not like the primary cost for fission is the fuel. It’s the recoupment of massive capex spend, cooling, maintenance, highly trained personnel.

I’m trying to show you that fusion isn’t going to magically rain energy mana down on us. It’s just fission with less waste (if you discount newer fission designs) except and potentially safer (if you discount newer fission designs) It’s likely significantly more expensive given it’s a more complicated reactor and we’ve built 0 commercially (and even with this achievement we’re not that much closer).

My point is, if you’re looking for boundless carbon-free energy, fission reactors already meet all the needs. Additional investments would get reactors that would generate waste competitive with fusion (and in fact can consume all existing generated waste as fuel) and are similarly safe (no runaway reactions).

I would encourage you, if you’re serious about carbon-free boundless energy, to devote your advocacy to advancing fission reactors. They’re here and there’s a straightforward R&D path to get the new reactors (regulatory hurdles are another thing). Fusion reactors won’t be here in any reasonable time frame (even if we had a workable design today it would take many decades to build them and then upgrade the grid).

Re: US Department of Energy: Fusion Ignition Achieved

#797

Post by eru »

eklitzke wrote: post #262
spullara wrote: post #165

Earlier quoted context omitted.

If you look at the mass before of their fuel, 1 deuterium atom + 1 tritium atom: 2.01410177811 u + 3.01604928 u = 5.03015105811 u vs the mass of the fusion products of 1 helium atom and 1 neutron: 4.002602 u + 1.008 u = 5.010602 u You'll notice that even though we started with 5 neutrons and 2 protons and ended up with the same number there was some additional binding energy that is unaccounted for in the new configu…

Tangentially related, but I think this is an interesting fact, all the atoms in our universe/galaxy/solar system with a mass up to that of iron are formed in the core of stars in stellar fusion. Hydrogen fuses into helium, and as a star nears the end of its lifetime you get heavier elements like lithium, carbon, and so on. Under normal stellar fusion no elements heavier than iron will be produced, and iron is only el…

If I understand this right, I think some of the lighter than iron elements are also created in those exotic processes. But yes, unlike for the heavier-than-iron elements, the lighter ones are _also_ created in normal stellar fusion.

Re: US Department of Energy: Fusion Ignition Achieved

#798

Post by moloch-hai »

wizofaus wrote: post #788
rerdavies wrote: post #786

Earlier quoted context omitted.

Tritium has a half-life of 12 years so there is no deep pool of tritium upon which to draw. The primary source of tritium on earth is cosmic-ray interactions in the upper atmosphere that produces 7.5Kg of tritium a year worldwide.[1] Isn't that going to cause a serious problem if it requires 323Kg/yr of tritium just to power New York City? [1] https://www.sciencedirect.com/topics/earth-and-planetary-sci...

Apparently no, because it can be made by the fusion process itself, via contact with lithium, and there's enough proven reserves of the latter to supply us for 100s of years.

Nobody knows how to get tritium at PPB concentration from the thousand tons of radioactive molten FLiBe it is dissolved in. You have to process all of it every day because you need that tritium for fuel tomorrow.

Re: US Department of Energy: Fusion Ignition Achieved

#799

Post by TeeMassive »

yk wrote: post #630
TeeMassive wrote: post #473

Earlier quoted context omitted.

H-bombs use the hydrogen to produce more neutrons which boosts the fission process. It still is a fission bomb.

No, you can have a fusion booster, like in the "Sloika" [0] design, but for a Teller-Ulam design, that is a H-bomb, you use a nuclear primer to ignite a fusion reaction and by far the most energy comes from the fusion part. [1] [0] https://www.atomicarchive.com/history/hydrogen-bomb/page-11.... [1] https://nuclearweaponarchive.org/Library/Teller.html

Half of the energy comes from the fissile "spark plug" that's inside the fusion material. Less than half of the energy comes from fusion.

It still very much is a fission weapon.

Re: US Department of Energy: Fusion Ignition Achieved

#800

Post by TeeMassive »

Analog24 wrote: post #575
TeeMassive wrote: post #473

Earlier quoted context omitted.

H-bombs use the hydrogen to produce more neutrons which boosts the fission process. It still is a fission bomb.

You have it backwards. The fission component is just the "trigger" for the fusion element, which produces the vast majority of the energy release.

Half of the energy comes from the fissile "spark plug" that's inside the fusion material. Less than half of the energy comes from fusion.

It still very much is a fission weapon.

Post reply on HN