MIT-designed project achieves major advance toward fusion energy • Hacker News Board

Re: MIT-designed project achieves major advance toward fusion energy

#371

Post by lambdatronics » Thu, Sep 09, 2021, 4:23 PM UTC

rnhmjoj wrote: post #50

anonuser123456 wrote: post #17

Earlier quoted context omitted.

> What's the catch this time? This is D-T fusion. Which means you have to have T. Which currently comes from fission reactor and has a half life of 15 years. So the plan is to use a molten salt blanket with Be to breed T. But Be isn’t scalable for consumption, so maybe lead eventually. That’s probably do-able, it just slows down the rate new reactors can come online since Pb is not as good a neutron multiplier. Once…

> But are they surmountable AND cheaper than existing nuclear or other energy sources? DT fusion solves the two biggest arguments that are always raised by nuclear energy opponents: storage of nuclear waste (it doesn't produce high-level waste) and safety (it's not perfect but it can't explode). I wouldn't call it a "meh", even if it comes off as much more expensive than fission.

Yeah, but nuclear energy opponents aren't the reason fission isn't getting built -- it's primarily about the cost.

Re: MIT-designed project achieves major advance toward fusion energy

#372

Post by lambdatronics » Thu, Sep 09, 2021, 4:30 PM UTC

nickik wrote: post #320

phscguy wrote: post #301

Earlier quoted context omitted.

Sadly no. While I think that it would work and probably be cheaper and easier than fusion, fission has an absolutely abysmal public image. People are terrified of radiation, even if the danger is very low. This means it becomes prohibitively difficult and hence expensive to build and run a fission plant because safety has to be prioritized so heavily. That is even if permission is granted to build in the first place.…

Fusion also produces radiation. So not sure why changing one word to the other should magically change public opinion. We can just rename fission to #goodenergy or something, that would be cheaper then developing fusion. People don't even know that nuclear reactors use fission, so the idea that this would change anything is crazy. People opposed will call fusion reactors 'nuclear' just like they do fission.

Yeah, I don't have much hope that the general public will understand the nuances here, especially if the greenies decide to mount a PR campaign against it. OTOH, we can call it "fusion" instead of "nuclear fusion" and that will undoubtedly help. (lol)

Fusion does indeed come with radiological hazards: a fire could release radioactive gas and dust. If designed right, the worst-case scenario would still be way less severe than for a fission plant -- and the worst-case scenario is really what stokes all the popular fears about 'nuclear'. OTOH, tritium leakage could mean that routine emissions are larger.

Re: MIT-designed project achieves major advance toward fusion energy

#373

Post by fouric » Thu, Sep 09, 2021, 4:30 PM UTC

codethief wrote: post #281

mchusma wrote: post #112

Earlier quoted context omitted.

You are right, people who flippantly dismiss fusion just don't understand it. -Fusion has made consistent improvement, roughly in line with expectations for the level of investment (20 years away predictions were considering if we invested massively, which we did not). - Fusion is in theory something that could give us true energy abundance. Want to just desalinate water like crazy? Want to extract gigatons of carbon…

> Fusion is in theory something that could give us true energy abundance. Well, at least for a few hundred years but then: > if you plot the U.S. energy consumption in all forms from 1650 until now, you see a phenomenally faithful exponential at about 3% per year over that whole span. The situation for the whole world is similar. […] the Earth has only one mechanism for releasing heat to space, and that’s via (infrar…

This idea seems like the CICO (Calories-In, Calories-Out) argument, and is misleading/wrong for exactly the same reasons - neither the Earth+people (or even just the Earth) nor the human body just stock energy like that linearly.

If you increase the amount of energy flowing into the human body, the metabolism increases as well (although almost never proportionally - there are many variables) to compensate.

Similarly, it's rather unlikely that humans will continue to use exponentially increasing amounts of energy, unless we intentionally do something to effect that. Human population growth, which is partially driving energy consumption, is not exponential (it would be exponential absent of resource constraints or cultural factors, but guess what - both of those are in effect rather strongly in the real world) - and neither is energy consumption per capita. For instance, from 2005 to 2020, the US gained 30M people[1] while keeping energy consumption roughly constant[2].

[1] https://datacommons.org/place/country/USA [2] https://www.statista.com/statistics/201794/us-electricity-co...

Re: MIT-designed project achieves major advance toward fusion energy

#374

Post by gghyslain » Thu, Sep 09, 2021, 4:37 PM UTC

fouric wrote: post #373

codethief wrote: post #281

Earlier quoted context omitted.

> Fusion is in theory something that could give us true energy abundance. Well, at least for a few hundred years but then: > if you plot the U.S. energy consumption in all forms from 1650 until now, you see a phenomenally faithful exponential at about 3% per year over that whole span. The situation for the whole world is similar. […] the Earth has only one mechanism for releasing heat to space, and that’s via (infrar…

This idea seems like the CICO (Calories-In, Calories-Out) argument, and is misleading/wrong for exactly the same reasons - neither the Earth+people (or even just the Earth) nor the human body just stock energy like that linearly. If you increase the amount of energy flowing into the human body, the metabolism increases as well (although almost never proportionally - there are many variables) to compensate. Similarly,…

You can’t just look at electricity consumption. You have to look at total energy consumption. Including the energy necessary to produce the goods you consume. And that is increasing exponentially.

In a way, the US (and Western countries) are outsourcing their energy consumption.

Re: MIT-designed project achieves major advance toward fusion energy

#375

Post by codethief » Thu, Sep 09, 2021, 4:39 PM UTC

gpm wrote: post #352

jeremyjh wrote: post #349

Earlier quoted context omitted.

> If we send big blobs of lava into space I honestly can't tell if you are joking. The energy expenditure to get anything into orbit would produce more heat than you are offsetting.

Depending on the design of the system, the energy could well be expended in orbit and not contribute to the heating of earth (think about designs like a space elevator). He's basically describing a giant air conditioner... it's definitely theoretically possible.

> it's definitely theoretically possible.

In theory yes, but in practice: Not so much.

Even if we put aside GP's concerns, shooting big blobs of lava into space would require heating up the lava/rock in the first place. But this process doesn't happen on its own (through thermalization) given the average temperatures on Earth, meaning that the process of moving waste heat (from the environment, i.e. air/ocean) to the lava will once again decrease entropy (of the combined lava + air/ocean system) and you thus need to move the missing entropy elsewhere. (Meaning that you have to do work to accomplish this heat transfer / dethermalization and you will once again incur waste heat.)

Sure, we could also try to tap the heat bath of the Earth's core but then we would build a deep-Earth elevator to transport lava and solid rock (or, say, water) back and forth and GP's concerns apply once more.

There's another option, though: Don't build an air conditioning system/fridge – use thermalization with another (lower-temperature) system. That is, don't take lava (or anything that needs to be heated beyond ambient temperature) – "just" take rock at (Earth's) ambient temperature, move it to a lower-temperature $PLANET and then move cool rock from $PLANET back to Earth. I doubt this would be very efficient/fast, though.

In any case, the difference between the two approaches is that an air conditioner (or a fridge) cools things below ambient temperature and requires additional energy for that (which it will expel as waste heat), while the second approach "simply" moves energy from the heat bath that is Earth to some lower-temperature reservoire (i.e. $PLANET). If $PLANET and Earth were thermodynamically connected not just through the exchange of infrared radiation, this would happen by itself over time through thermalization.

Re: MIT-designed project achieves major advance toward fusion energy

#376

Post by codethief » Thu, Sep 09, 2021, 4:43 PM UTC

regularfry wrote: post #327

codethief wrote: post #297

Earlier quoted context omitted.

> into motion Kinetic energy will end up getting converted to waste heat nonetheless. > or bound carbon This seems hard to imagine. We're dealing with waste energy here, so a very high-entropy type of energy. Bound carbon is low-entropy, so the conversion is impossible[0] unless we put that entropy elsewhere. As an analogy, consider a fridge: It brings your food from a high-entropy (high-temperature) to a low-entropy…

We're not necessarily talking about a closed system, though. If you've got an energy supply that rounds to limitless, constructing planet-scale heatsinks starts to look tenable.

> We're not necessarily talking about a closed system, though.

Short of shooting hot lava into space[0] we pretty much are because, once again, thermalization through radiation is governed by Stefan-Boltzmann's law and there's no way around that.

[0]: https://news.ycombinator.com/item?id=28468182

Re: MIT-designed project achieves major advance toward fusion energy

#377

Post by codethief » Thu, Sep 09, 2021, 4:46 PM UTC

zo1 wrote: post #355

codethief wrote: post #303

Earlier quoted context omitted.

> but interstellar travel would not be much of a challenge with that sort of energy abundance. I don't think I agree. 1) The extremely high (but still finite) amount of energy required to evaporate the Pacific Ocean is still much less than the infinite energy you need to accelerate even one single space traveler to the speed of light. Infinity is weird. Of course we won't be trying to reach the speed of light but the…

Not quite sure I follow. On earth we're mostly limited to radiation to get rid of excess heat, I understand that part. But on a space-ship, can we not just expel the heat via mass? I.e. We super-heat some dense materials and just shoot them out.

Where will you be getting all that mass from, though?

> We super-heat some dense materials

This won't work as you would need to put in additional work (leading to additional waste heat) in order for this process to lower ambient temperature. The only thing you could do is shoot stuff out that's precisely at ambient temperature, compare https://news.ycombinator.com/item?id=28471620 .

Re: MIT-designed project achieves major advance toward fusion energy

#378

Post by acchow » Thu, Sep 09, 2021, 4:58 PM UTC

ifdefdebug wrote: post #289

codethief wrote: post #281

Earlier quoted context omitted.

> Fusion is in theory something that could give us true energy abundance. Well, at least for a few hundred years but then: > if you plot the U.S. energy consumption in all forms from 1650 until now, you see a phenomenally faithful exponential at about 3% per year over that whole span. The situation for the whole world is similar. […] the Earth has only one mechanism for releasing heat to space, and that’s via (infrar…

Well if we transform solar into electric then into motion or bound carbon, that should actually help reduce the heat balance?

But then what do you do with that motion?

Eventually it all decays to heat, as per the 2nd law of thermodynamics

Re: MIT-designed project achieves major advance toward fusion energy

#379

Post by codethief » Thu, Sep 09, 2021, 5:17 PM UTC

Aeolun wrote: post #333

codethief wrote: post #303

Earlier quoted context omitted.

> but interstellar travel would not be much of a challenge with that sort of energy abundance. I don't think I agree. 1) The extremely high (but still finite) amount of energy required to evaporate the Pacific Ocean is still much less than the infinite energy you need to accelerate even one single space traveler to the speed of light. Infinity is weird. Of course we won't be trying to reach the speed of light but the…

> The extremely high (but still finite) amount of energy required to evaporate the Pacific Ocean is still much less than the infinite energy you need to accelerate even one single space traveler to the speed of light. True, but how many tons of space junk can you accellerate to 95% of light speed for the same amount of energy?

Quick back-of-the-envelope calculation:

    Approx. mass of Pacific Ocean[0]: m_ocean = 7.1×10²⁰kg
    Specific heat of water: c = 4.2kJ/(kg · K)
    Temperature of Pacific Ocean: T_1 ~ 293K
    Temperature at which water starts boiling: T_2 ~373K

=> Energy needed to make Pacific Ocean boil:

    E_heat = c m_ocean ΔT = c m_ocean (T_2 - T_1) ~ 3×10²⁶ J

On the other hand, the relativistic kinetic energy formula is:

    E_kin = (γ-1) m c²,

where γ = 1/sqrt(1-v²/c²) = 1/sqrt(1-0.95²) and m is the space junk's mass.

Setting E_kin = E_heat therefore yields:

    => m = E_heat / [(γ-1)c²) = 3×10²⁶ J / (2.2×10¹⁶ m²/s²)] = 10¹⁰ kg

For comparison: The mass of all of humanity combined is somewhere between 10¹¹kg and 10¹²kg. Now those numbers do look somewhat comparable but:

- We haven't taken into account the space ships required to transport everyone

- E_heat was waste heat but since practically all energy will become waste heat at the end of the day, E_heat gives us a pretty good estimate of the total energy we will have (had) access to.

All in all 0.95·c doesn't seem feasible for moving humanity to Proxima Centauri, given E_heat. For moving 10¹⁰ kg of space junk, sure, though I'm not sure what you were planning to do with all that space junk in the first place?

[0]: https://en.wikipedia.org/wiki/Pacific_Ocean

Re: MIT-designed project achieves major advance toward fusion energy

#380

Post by codethief » Thu, Sep 09, 2021, 5:19 PM UTC

gghyslain wrote: post #374

fouric wrote: post #373

Earlier quoted context omitted.

This idea seems like the CICO (Calories-In, Calories-Out) argument, and is misleading/wrong for exactly the same reasons - neither the Earth+people (or even just the Earth) nor the human body just stock energy like that linearly. If you increase the amount of energy flowing into the human body, the metabolism increases as well (although almost never proportionally - there are many variables) to compensate. Similarly,…

You can’t just look at electricity consumption. You have to look at total energy consumption. Including the energy necessary to produce the goods you consume. And that is increasing exponentially. In a way, the US (and Western countries) are outsourcing their energy consumption.

> Including the energy necessary to produce the goods you consume.

Exactly, the original link I posted is more or less an argument against infinite economic growth.