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

Compact nuclear fusion reactor is 'very likely to work,' studies suggest

nytimes.com

Post reply on HN
Print view View original

281–290 of 373 posts

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#281

Post by jnxx »

pfdietz wrote: post #110
Baeocystin wrote: post #77

Earlier quoted context omitted.

>The plasma heats up, but how do you turn that into useful electrical energy? I appreciate that many people are commenting 'you couple the plasma to a working fluid', but I think the original comment was more along the line of how you couple a confined plasma to a working fluid. By definition the plasma is in a hard vacuum, magnetically bottled. What, then, is the coupling method? Thermal photons escaping confinement…

80% of the energy from DT fusion comes out as neutrons, which enter a blanket and deposit energy there by collisions and nuclear interactions.

> which enter a blanket

So, what is that blanket made of?

It needs to be a material which:

- can withstand high temperatures and radiation

- does not becomes radioactive itself

- facilitates production of Tritium by breeding

- operates in very high magnetic fields, which means high forces

No such material is known so far.

It is a bit like some engineer from 1700 said: "Well, you could just build a more efficient and compact and light steam engine, and connect it to a machine which has flapping wings, and then you have a transport vehicle which can carry people across the Atlantic ocean at supersonic speed, and at little cost."

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#282

Post by kamaal »

mchusma wrote: post #72
jhoechtl wrote: post #52

Honest question: Has man-made nuclear fusion ever happened? Or is it theory, happening on the sun?

Yes man-made nuclear fusion is quite "easy". The hard part is getting more energy out than you put in. The sun does this all the time, basically by having so much mass that hydrogen gets sucked in by gravity to collide with other particles. Keeping hydrogen close enough to smash into each other is hard, the sun is just so big that it can do that. Hydrogen bombs do this by using other explosives to push hydrogen toget…

>>The hard part is getting more energy out than you put in.

I thought this was impossible due to law of conservation of energy.

Well eventually we get lucky with things like gravity, and water cycles doing the work for us by giving us rivers and we build a dam around it.

But you can never design a process where you can take more than what you put in.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#283

Post by tuatoru »

notJim wrote: post #146
dnautics wrote: post #127

Earlier quoted context omitted.

You don't know that. What if you had spent 1000x the budget of the manhattan project on building an atom bomb in the year 1789? You would have gotten squat.

I don't think that's quite an apt comparison. The fundamental physics of an atomic bomb were not well known until the late 1800s. Apparently the Manhattan Project cost about $23 billion in 2007 dollars. ITER apparently had an initial budget of around $5 billion in 2005-6. By now, the construction cost is estimated to be at least $22 billion. It seems plausible that if we throw $15 or 20 billion at it in 2006, we coul…

> The fundamental physics of an atomic bomb were not well known until the late 1800s.

Er, don't you mean the early 20th century?

Rutherford's exegesis of the nuclear model of the atom was published in 1911.[1]

1. https://en.wikipedia.org/wiki/Rutherford_model

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#284

Post by tuatoru »

willis936 wrote: post #19
isoprophlex wrote: post #8

I never quite understood the math behind power densities in a fusion reactor. In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW? Is the density of the plasma so much higher in a fusion reactor? Also, something else I never grokked, how d…

The density is actually lower than the sun in magnetic confinement fusion (MCF) devices because we can’t squeeze plasma together as hard as the sun’s mass can. Inertial confinement fusion (ICF) can squeeze harder than MCF devices, but has serious unaddressed engineering issues. The trick is in higher temperature plasma. The sun fuses protium (lone protons). We don’t have the confinement necessary on Earth to do this,…

Project Rho has lay-person accessible detail on type of fusion reactions.[1] Well worth a read. The takeaway is, if we can't do D-T fusion, then don't even think about any of the other kinds. They're orders of magnitude harder.

1. http://projectrho.com/public_html/rocket/fusionfuel.php

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#285

Post by tuatoru »

jnxx wrote: post #281
pfdietz wrote: post #110

Earlier quoted context omitted.

80% of the energy from DT fusion comes out as neutrons, which enter a blanket and deposit energy there by collisions and nuclear interactions.

> which enter a blanket So, what is that blanket made of? It needs to be a material which: - can withstand high temperatures and radiation - does not becomes radioactive itself - facilitates production of Tritium by breeding - operates in very high magnetic fields, which means high forces No such material is known so far. It is a bit like some engineer from 1700 said: "Well, you could just build a more efficient and…

Not such a bad analogy, as the blanket will get hot, and the heat will be used to turn water into steam, which will power generating plant. Just like in the 18th and 19th centuries.

It would have had to have been an unusually well informed and far-sighted engineer though, as Savery's engines first worked in 1698 and the first for-sale commercial engine, Newcomen's, wouldn't happen until 1712. And they were incredibly inefficient: 0.01% to 0.1%.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#286

Post by Retric »

ClumsyPilot wrote: post #183
m0zg wrote: post #109

Earlier quoted context omitted.

Just the little bit responsible for Chernobyl and Fukushima is not a part of the design at all. No big deal. :-)

I am really tired of this line - the taunami killed 18,500 people. The reactor incident killed no-one through radiation and 32 people through physical injuries. One failure of Banqiao Dam killed an estimated 240,000 people. That's more than all people who have ever died from anything to do with nuclear, reactors and bombs combined. Air pollution kills about 2,000 people every single day. Reactor incidents are like pl…

Killing people is hardly the only issue. Rendering large tracts of land uninhabitable is extremely expensive. All told 4 nuclear reactors have had major issues, 2 subs and 1 power plant run by the USSR, and then another one very recently by Japan. Plus several near misses.

That’s a significant percentage of total reactors ever built including what was considered a safe design. We could go 1000 years without another incident, but from an insurance standpoint what would you charge a new power plant next to NYC? That means you need them in an a less expensive area, but everyone feels their area is valuable. That causes vast NIMBY issues and heavy regulation.

In theory modern Nuclear should cost less and be both clean and safe, but people gonna people both inside and outside the industry.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#287

Post by tuatoru »

kamaal wrote: post #282
mchusma wrote: post #72

Earlier quoted context omitted.

Yes man-made nuclear fusion is quite "easy". The hard part is getting more energy out than you put in. The sun does this all the time, basically by having so much mass that hydrogen gets sucked in by gravity to collide with other particles. Keeping hydrogen close enough to smash into each other is hard, the sun is just so big that it can do that. Hydrogen bombs do this by using other explosives to push hydrogen toget…

>>The hard part is getting more energy out than you put in. I thought this was impossible due to law of conservation of energy. Well eventually we get lucky with things like gravity, and water cycles doing the work for us by giving us rivers and we build a dam around it. But you can never design a process where you can take more than what you put in.

You're forgetting the mass-energy equivalence, E = mc^2.

Both fission and fusion are elaborate ways of converting a small fraction of the mass of the fuel to energy.

Also, "you can't get more than you put in" applies to closed systems. Reactors are open systems.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#288

Post by phicoh »

baking wrote: post #229
ada1981 wrote: post #159

Earlier quoted context omitted.

This is a great mental model. I'm curious about applying this in areas of one's own life. Certain things that you'd actually accomplish faster, by starting later and leveraging the compounded time / resources that would have been spent pursuing it earlier.

OT, but if solar panels last for over 20 years and get at least 5% cheaper every year, you save more money by waiting to install them than you do by installing them.

That does not factor in the money you make with the solar panel. I.e., if having a solar panel nets a profit of 10% of the cost of the solar panel, than installing one now makes more money than waiting a year.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#289

Post by DennisP »

jnxx wrote: post #276
varjag wrote: post #260

Earlier quoted context omitted.

That's a luxury problem at the moment. A fusion reactor that can sustain positive output operation for 5 years is still a dream.

It is a total show-stopper because you don't have the amount of Tritium to power such a reactor.

We have plenty of lithium. All D-T fusion designs breed tritium from lithium, using the high-energy neutrons from the reaction.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#290

Post by DennisP »

jnxx wrote: post #275
physicsguy wrote: post #259

So, I'm a physicist, and I went to a number of talks from people involved with the JET fusion reactor over the years, though fusion is not my area. And my understanding is not that it's difficult to make plasma, or even build a reactor in particular that is the main problem (though instabilities can be problematic), but it's that the internal structure degrades very rapidly and becomes highly radioactive, because you…

Applied physicist here. The other thing is: Existing fusion concepts need to use a reaction between Deuterium and Tritium, otherwise it's just infeasible. Deuterium exists in nature and can be produced with some form of isotope separation. Tritium, however, does NOT exist in nature, and can only be conceivably produced in three ways: 1. Inside thermonuclear bombs 2. In heavy-water reactors, e.g. CANDU design, which r…

SPARC uses molten FLiBe salt as both coolant and breeding blanket.
Post reply on HN