Reply To: What can we do with $189 Billion?

[zapkitty]

fixed your quotes up above

Tulse wrote:
Once you need [em]any[/em] sort of steam-turbine-generator setup, that presumably wipes out almost all the capital savings, right?

Yes, the steam turbine gear, generator, supporting waterworks and the maintenance for it all are the largest portion of the costs of building and operating a current fossil or fission power plant.

And, as with a fission plant, a D-T fusion plant would also use its neutron output to heat water to create steam to turn turbines to power a generator etc. etc.

This has been regarded as the de facto standard design for fusion reactors as the D-T reaction is the easiest to achieve and ~80% of the energy output of the D-T reaction goes into the neutrons produced.

Tulse wrote: Sure, you might be able to get away with a smaller turbine and generator, but I would think the main cost is the physical plant and gear associated with [em]any[/em] sort of steam generation.

One way around it would be to discount the neutronic output of the D-T reaction as a loss… to only use it for breeding tritium from lithium.

But this would require a high gain factor from the reactor. Let’s say the reactor has an energy gain factor (Q) of ~10… ITER is expected to have a Q of ~10 and the follow-on DEMO project a Q of maybe 25.

So with a Q of 10 then 1 MW of input would get you 10 MW of output. That would be about 2 MW of directly convertible fusion products and 8 MW of neutrons.

(Unlike steam turbines the various direct conversion processes can be [em]very[/em] efficient. 80% efficiency is a reasonable goal.)

So if you discount the neutron output then the 2 MW left over becomes ~1.6 MW after direct conversion.

Your gain factor of 10 becomes a factor of 1.6… but you get rid of the expensive, bulky and costly to maintain steam-related gear.

The tech details in the release are almost non-existent but it’s possible that this approach would be worthwhile. And maybe Helion figures they can finesse these ratios a bit.

… so that pdf mentions a ~50 MW reactor… but is that the total fusion output or is it 50 MW electric delivered to the grid?

50 MW total output would get you 8 MW to the grid… like an FF module but with the added expenses of intense neutron flux, tritium breeding and handling and highly radioactive components in the waste
stream.

If it’s 50 MW to the grid then the raw fusion output would be in the 310 MW range … with ~248 MW worth of neutron flux to just breed tritium, radioactivate the burn chamber and, of course, to be converted into heat and rejected from the reactor somehow.

Tulse wrote:
In other words, if they’re not fully direct generation, I’m not sure how they can claim that there is any significant capital savings.

If they intend to direct convert what they can, and just use the neutrons for tritium breeding, then the description could make sense.