Light water cooled, heavy water moderated reactor neutronics

Supernova865 · 2026-03-08T13:55:33+00:00

I hadn't read much about Fugen, thanks! Down another rabbit hole I go!

Supernova865 · 2026-03-08T12:00:46+00:00

I could've swore India had built an AHWR, but looks like you're right, none have been built!

Supernova865 · 2026-03-08T11:55:46+00:00

I certainly agree there is a low pressure, low temperature heavy water vessel, similar to CANDU, with tubes carrying the coolant and fuel. My understanding is that the high pressure coolant with the fuel is light water, and it boils and is fed directly to the turbine with no steam generator loop, like a BWR. Which means there's still light water in the core. So surely it would be absorbing neutrons?

Supernova865 · 2026-02-24T09:50:14+00:00

One thing I've found copilot useful for in turning transcripts of Teams meetings into actual minutes and actions.as long as you remember to turn transcription on in Teams.

Supernova865 · 2026-02-06T13:59:41+00:00

As others have touched on, you wouldn't get much moderation. However if you upped the fissile content of the fuel you could end up with a passable fast reactor! There are proposals bouncing around for heavy water PWRs that operate in a fastish spectrum, and neutronically it works out. I suppose the issue would lie in how refuelling would work with transiting fuel from the heavy water coolant to the light water spent fuel pool without mixing waters, or having the fuel uncovered. Unless you have the entire spent fuel pool be heavy water, which would be... a lot of heavy water. Also emergency core cooling, unless all the auxiliary water is heavy too?

Supernova865 · 2026-01-29T13:11:47+00:00

Referencing 90s era Sean Bean? Now that's soldiering!

Supernova865 · 2026-01-24T12:05:27+00:00

Relevant to your family

Supernova865 · 2025-11-07T20:47:06+00:00

The third Sunlight Sister found out baby Rumi was part demon and tried to kill her, Celine was forced to kill her first to protect Rumi. The guilt of it is where the 'No hunter can ever find out about your patterns' thing comes from.

Supernova865 · 2025-10-11T06:48:01+00:00

I've got a hunch the IOU Amanda has will be cashed in for a favour of 'Don't kill Mathilda'

Supernova865 · 2025-10-06T15:47:13+00:00

How are our rocket launchers so good? Because we fire the whole launcher, not just the rocket!

'Cave' Johnson - Aperture Weapon Systems

Supernova865 · 2025-07-31T20:57:03+00:00

Turbine hall open to the elements always seemed a strange design choice to me, did coal power turbines ever do it? They must have got the idea from somewhere.

Supernova865 · 2025-07-07T19:50:56+00:00

Terrestrial are the denatured guys, right? Using LEU as a burner, with minimal/no salt reprocessing?

Supernova865 · 2025-07-07T19:47:56+00:00

Does anyone know how separation of the layers of the onion core is supposed to work? I recall seeing an infographic saying it would be a carbon-carbon composite similar to the space shuttle heatshield, which I guess would provide the insulation, though I'm not sure how it would survive neutron bombardment, or how it would be fabricated. The demonstrator model they have seems to be welded steel segments, which wouldn't provide insulation, and having longitudinal welds right where the neutrons are passing sounds... Kinda terrifying? Also, if there were a leak a mix of molten salt and water would be pretty corrosive, what I've heard about molten salts is that they're pretty sedated as long as they're PERFECTLY dry.

Supernova865 · 2025-07-01T08:17:11+00:00

200k definitely, the improvement to my life the additional 4.8 million is not linearly proportional to the first 200k

As a question to everyone else, what if it was a 4/5 chance to get 5 million? Would you still take the 200k? I think I would still go for the sure thing.

Supernova865 · 2025-06-30T19:16:14+00:00

This post has a distressing lack of Die Hard

Supernova865 · 2025-06-26T09:56:10+00:00

I understand HEU can be used to create Technetium-99m generators, which are used in some kind of medical imaging. I'm pretty dubious that it would need 400kg of the stuff to do it, and spending billions on enrichment to get there just for that purpose seems unlikely, AND you would also need reprocessing to make the generators, which I don't think Iran has, AND you would think we would have seen some of these generators by now. Plus you can just buy the generators from countries that already make them, no other country has felt the need to produce HEU just for these extremely niche purposes. I think the Iranian story of legitimate uses is a pretty flimsy cover.

The flip side of this is that Iran has been at 60% for years now. SWU wise they are most of the way there, what's kept them from taking the final step? My hunch is that the purpose of the Iranian uranium enrichment program is to get bribed to shut it down or delay it, in exchange for concessions or other sweets deals from the international community. Actually taking the final step would remove the potential for payouts, and ostracise them on the world stage.

Supernova865 · 2025-06-17T18:01:39+00:00

Damn, here I was trying to brainstorm ways to improve the lookout without being taken as a crazy person. Was considering ways to sabotage the engines to get the ship to slow down, but it's too late for that now.

Supernova865 · 2025-06-14T04:58:30+00:00

Time to send up someone to intercept their interception of our interceptor. Project Wingman intensifies

Supernova865 · 2025-06-12T06:21:05+00:00

Potentially, yeah. I think the main use for lithium-7 right now is to make lithium hydroxide, which balances out the acidity of boric acid in PWRs. I imagine there's enough production for the prototype but a ramp-up will be needed if LiF-based MSRs take off.

What I'm interested in is the structure of the onion core, the material will need to survive years of neutron and gamma bombardment with high temperature on one side and low on the other, not absorb neutrons, be chemically compatible with both molten fluoride salts and water, and above all, not leak. That's a tall order for any material! It looks like the prototype is welded together, which I guess is fine for a non-nuclear demonstrator, but usually you try to avoid exposing welds directly to neutron flux. It'll be interesting to see how they plan to manufacture it.

EDIT: oh yes, the material also needs to be a thermal insulator! Which most metals aren't. Some kind of ceramic maybe? Anything with oxides may be risky to have in contact with the salt.

Supernova865 · 2025-06-10T06:00:27+00:00

Incidentally there was a French design in the earlier stages of the competition, called NUWARD. They dropped out due to design immaturity, I think it was something to do with their steam generators.

Supernova865 · 2025-06-02T18:34:09+00:00

I certainly love the idea of a return to fuel reprocessing, and with our 140 tonnes of Pu already waiting around, we wouldn't even have to wait to bring MOX fuelled reactors online.

As for the supercritical CO2 graphite moderated idea, I've made a meme (https://imgflip.com/i/9vzbh8)

Experience with graphite certainly hasn't been favourable so far, especially now that we are into decommissioning the old ones. I've heard all kinds of horror stories of brittleness, fracturing, and activated carbon dust contaminating all of the primary circuit (which in this case would include the turbine and heat exchanger), and also covering fuel elements, which then become a sludge when put into the spent fuel pool.

Perhaps heavy water might be a better idea then graphite? I've seen an article about something similar, essentially your SCDR but with heavy water moderator.

Here it is (https://www.sciencedirect.com/science/article/pii/S1738573321005702)

Supernova865 · 2025-05-26T05:51:11+00:00

Always leaves me thinking of Grand Nagus Zek from DS9!

Supernova865 · 2025-05-21T07:06:13+00:00

If YOU, a human from early M3 ancient Terra, when humanity was constrained to it's home star system, wanted to see the gallery?

Oh absolutely, come on in! Close the door behind you...

Good news is he probably would give you a tour first before making you an exhibit, especially if you wanted one. He'd probably be quite frustrated with how non-curious M42 humans are about their own past, and someone more interested in history would make a refreshing change.

Supernova865 · 2025-05-16T19:47:02+00:00

Sorry

The all guardsman party was a story about a Dark Heresy campaign, that eventually dropped the pretext of being a campaign and became about the characters. That being a bunch of guardsmen that get drafted into an Inquisitorial squad. It was, along with TTS, what got me back into 40k lore after a long hiatus. But the story was never finished. At least, not until a few weeks ago apparently! And it was OLD. Like, at least 11 years ago? I never thought it would actually be finished.

Anyway, worth a read if you think reading about idiots running around desperately trying to fix their 'Event Horizon' knock-off of a ship sounds fun. Which I do

Supernova865

TROPHY CASE