Reply To: turn heat into electricity

[Maya]

zapkitty wrote:

…?

Could you explain why you think that “at least hundreds of gigawatts” are required for a commercial fusion reactor?

Even the largest current fossil and fission power plants are at most 1-2 gigawatts per unit.

Or did I misunderstand and it’s the fusion concept you mentioned that requires that minimum size to be viable?

Yep, you did. The discussion is about fusion. Which costs more to build and run? Savannah River Site or ITER? And remember how little power ITER will produce. Fusion power plants will be economic monsters that have to be actuarially sound. I think this is part of the problem with the public perception about fusion. There’s a lack of economic reality in the proposals. Iff you could build a fusion reactor that is super cheap, that might change, but somehow I doubt that’s going to happen.

zapkitty wrote:
… a 21 terawatt pB11 reactor?

Why on Earth (and where on Earth) would you want to build a single reactor that would supply over half again the entire world’s current power needs?

It’s about cost and economics. In order for fusion to be seen as a replacement that can idle other plants it must not only produce enough power to justify its cost, it likewise must produce power so abundantly that it expands that market. Do you think that energy consumption will remain constant over the next 50 years? I don’t. I think it will skyrocket.

zapkitty wrote:
The pB11 reaction is aneutronic in nature and units built along the lines envisioned by Focus Fusion, Tri-Alpha and the Polywell concept would be in the scale of a few megawatts to a gigawatt or so and their neutron flux would be pretty damn small.

It seems that you’ve set impossible-to-meet criteria and I look forward to learning what you envision as the solution to them 🙂

I don’t think so. I think the criteria are grounded in hard reality. I don’t believe that megawatt class fusion reactors will ever be economical in any foreseeable future. On this particular point the issue isn’t technical. It’s economic. Why would anyone build a megawatt class reactor that would be such a colossal construction for a single one-off? And the four key issues I described are part of the reason why I don’t think they’ll be economical. Even if you lower the power output you will still have phenomenal pressures to deal with. Have you looked at the structural loading on ITER; a reactor that can barely power a lawnmower? They’ve got the numbers on their website if you’re curious. Even at these totally uneconomical power levels it experiences several million kg*s of force to its structure. These pressure calculations are pretty basic calculations. And before you think that’s just because of those magnets, ask yourself, why do the magnets need to exert all that force? Answer: pressure. Now, given a favorable reaction rate ask how much fuel product must be present to get a worthwhile power density in the plasma and you will see my point. As you pack the material closer and closer the pressure necessarily goes up. Power and pressure have a defined mathematical relationship in thermonuclear fusion and they scale together as a square.

Yes, I know, youtube is replete with one venture capital con after another talking about producing fantastic amounts of fusion power with virtually no mention of pressure. But that’s not reality. It’s fiction and IP games. If that doesn’t make it clear, you can also run a power calculation and estimate equivalent reaction force against the vessel. That will also make it clear. It doesn’t matter how you _do_ the fusion. The problem here is more fundamental than that. Fusion at bottom is a power conversion problem of a magnitude of which the public is not generally well aware.

In the case of fission plants producing 1 or 2 gigawatts, the energy transfer is through very large, very heavy turbine machinery that distributes what would otherwise be pressure on a fusion reactor vessel. But, it’s still only a couple of gigawatts. But more fundamentally and to my point, fission doesn’t rely nearly as much on pressure (or reaction forces generally) … because its fission … not fusion.

If you have an Ph.D in physics and will sign an NDA I’d be glad to share my thoughts on a solution with you. I’m not being hokey or pessimistic at all. I believe there _is_ a solution, but it’s not on youtube and there is a lot of incentive out there to sell intellectual property instead of creating fusion power. If we’re going to solve the fusion riddle we have to understand what the technological impediments actually are, and very few people do. Sadly, academia isn’t helping because they want the big bucks for what they well know is nothing but pure science with no near-term application merit. That’s my take on con-Fusion Wonderland.