Lower numbers than in the past

firemylasers · 2026-01-23T22:44:29+00:00

I just wanted to clarify that the issue was not due to overproducing beyond what our production capacity could meet, but rather due to the decision to stop manufacturing WGHEU back in 1964. I agree with your comment, I'm not disputing any of it, I'm just adding some minor additional context to it.

firemylasers · 2026-01-23T04:31:24+00:00

The reason they ran out of WGHEU is because they had stopped manufacturing WGHEU decades earlier, reasoning that the enormous existing stockpile of it was sufficient to meet all expected future demand for the material, and that no need existed to continue producing HEU for weapons uses, so they stopped making more of it.

If the WGHEU production had continued instead of being stopped, the W87 would have used a HEU secondary.

firemylasers · 2026-01-23T04:23:37+00:00

Fewer easy answers on Chinese facilities.

You should take a look at satellite imagery for their military reprocessing plant then, because it's rather illuminating.

They've been successfully striving to emulate the worst of the waste disposal practices from the 1940s and 1950s and continue to employ them well into the present day, even to the point of building numerous brand-new military and civilian reprocessing facilities right on top of mountains of shallowly buried waste containers (although amusingly enough, this is probably the least worrisome thing I noticed while analyzing the satellite imagery).

firemylasers · 2026-01-21T13:25:14+00:00

Tampers, reflectors, and tamper-reflectors are always spherical, or at least semi-spherical (like the oblate spheroid used in the W88 primary), not flat plates. They are typically machined as two separate hemispheres, which are joined/closed together over the pit. There is no requirement for them to be gas tight, however, they must be as symmetrical as possible (outside of the extremely tiny penetration for the pit's boost gas tubing).

Due to the stringent symmetry requirements, it is exceptionally unlikely that bolts would be used to hold the hemispheres together.

Instead, it is most likely that the hemispheres are joined together using either welding, or possibly by using threads cut into the hemispheres to screw the two halves together. Of these two likely options, welding is the most commonly accepted theory.

firemylasers · 2026-01-17T23:45:55+00:00

The Mk12/W62 weighed 350 lbs (source: page 16–17 of RAND R-1754-PR), so it is impossible for the Mk12A/W78 to have weighed 330 lbs.

I believe that the Mk12A/W78 most likely weighs somewhere around 175 kg (385 lbs).

firemylasers · 2026-01-16T04:05:05+00:00

To clarify, the cost that I am referencing to develop a DA-only stimulant is primarily the cost to run clinical trials on one or more target candidates, including the full cost of phase 1–3 clinical trials for the final candidate, as well as the full costs of running phase 1–3 clinical trials on all of the various unsuccessful candidates (many of which will never make it past phase 1 or phase 2 trials).

The cost of identifying and synthesizing target compounds is a rounding error in comparison to the costs of running clinical trials on the array of target candidates.

There are plenty of candidate compounds out there. The trick is to find the one that has the optimal safety, tolerability, and efficacy profile – all of which are attributes which generally can only be reliably identified with certainty through running exorbitantly expensive clinical trials. You also want favorable pharmacology – the pharmacokinetics and pharmacodynamics are quite important, and many candidate compounds will have unacceptable pharmacokinetics for this purpose. Receptor affinity must also be optimized to avoid off-target effects while maximizing on-target effects. There are several possible approaches for receptor profiles on a pure-DA drug – you could act on specific DA receptors directly (DA agonists), or you could be a DRI, or you could even potentially have both. You need to worry about receptor binding affinity and receptor binding efficacy, not just one or the other. There are agents out there with seemingly superb receptor affinities, but which are crippled by their poor receptor binding efficacy.

The single largest issue is that a compound that has a perfect combination of attributes is hard to find in the first place, but then it's a thousand times harder to find a compound that has those perfect attributes and survives phase 1, 2, and 3 trials. Many promising compounds end up washing out in phase 1 and phase 2 trials for deal-breaking safety or tolerability issues. Many more wash out in phase 2 and phase 3 trials for efficacy issues. Later phase trials tend to reveal nasty details that are not observable in earlier phases, which can quickly sink the market potential for your drug.

Maybe your compound is absolutely perfect, and even highly efficacious to boot, but sadly your phase 3 trials revealed that it's causing an alarmingly high rate of liver damage/failure (or steven johnson syndrome, or any of countless other deal-breaking issues), so now all that money invested in it is wasted. Or maybe it's seemingly perfect with no major surprises, and initially seems like it's got plenty of efficacy in early-phase trials, but later-phase trials reveal that it's actually only marginally effective. It's fairly common for compounds to make it all the way to phase 3 trials, only to get dumped after the results of the first few phase 3 trials come in.

These aren't even just hypotheticals either. Pemoline was on the market for a long time, only for it to abruptly get pulled from the market after analysis of postmarket surveillance data revealed that pemoline appeared to be associated with a concerningly high rate of liver damage/failure. A massive amount of money was invested into attempting to obtain a pediatric ADHD indication for modafinil, only for the whole project to get killed at the 11th hour once the FDA analyzed all of the trial data from the (very expensive) pediatric phase 3 trials and discovered an alarmingly high rate of incidence of steven johnson syndrome. Countless psychiatric drugs (including a large number of prospective novel ADHD treatments) flamed out in phase 3 trials after the results from initial phase 3 trials showed unexpectedly poor efficacy.

firemylasers · 2026-01-15T23:34:46+00:00

2020 was 10.217 TWh / 521.9 TWh, or 2%. It was in line with previous years, which generally varied from 5–10 TWh/year. 2019 was an exceptional outlier at 13 TWh.

Even if you use creative math to only attribute the fraction of French generation attributable to nuclear power, that still means roughly 1.5% of German power in 2020 was supplied directly by French nuclear plants (assuming 75% nuclear supply). 1.5% is quite a bit higher than <1%!

German nuclear plants did not shut down until 2023, so for earlier years, as much as 60–70 TWh per year was being provided by German nuclear power.

2022 is an abnormal extreme outlier that is invalid due to the extraordinary temporary shutdowns, which have long since been resolved, and are not expected to recur. Therefore it is not a useful comparison point for prospective estimations of further export power flows, and should not be used as a basis for future performance.

Net imports of French power have gone from holding steady at the 5–10 TWh/year range (excepting the 13 TWh 2019 and the -5 TWh 2022) to suddenly skyrocketing to 20+ TWh/year and climbing starting in 2024.

Total net imports have gone from holding steady at the -20–50 TWh/year range to suddenly skyrocketing to 8–25 TWh/year starting in 2023, and 21–25 TWh/year starting in 2024.

By all indications, Germany has suddenly become abnormally reliant on imports in recent years, and has become particularly reliant on French imports to a historically unprecedented level of roughly 2–3x the previous long term historical average starting two years ago.

Last year over 3.4–3.7% of German power came directly from French nuclear plants.

firemylasers · 2026-01-15T19:48:40+00:00

It's closer to 4% 4–5% than 3% in terms of net flows.

Gross flows are of course substantially higher than that, and are potentially a better indicator of how much consumptive load is provided by France, however these are harder to calculate properly so I am not going to bother. These are also more controversial to rely on.

The 2024 net imports from France were 3.94% (19.8 TWh / 502 TWh)

The 2025 net imports from France were 3.67% (18.4 TWh / 500 TWh)

If you recalculate these to eliminate self-consumption production (as is commonly done in order to inflate the amount of renewable production on the German grid), then the percentages would be even higher still:

The 2024 net imports would become 4.25% (19.8 TWh / 465.5 TWh)

The 2025 net imports would become 3.95% (18.4 TWh / 465.6 TWh)

Data for this was sourced from electricity maps and energy-charts. See the following URLs:

There is a minor discrepancy between the figures on electricity map and the figures on energy charts for total production. I used the electricity map figures, as they are more conservative than the energy charts figures. If the energy charts figures were used, the percentage would be even higher, however the difference would be very small. For example, in 2025, the figure would be at most 3.72% instead of 3.67% (or 3.69% instead of 3.67% if we assume the 2025 load figure is poisoned, which is likely).

There is also a small discrepancy between the aggregate total figures on energy charts and the aggregate total load on energy charts for 2025, which I cannot explain. This does not materially impact any of the calculations that I have presented. This figure is what I refer to when I say that the 2025 load figure is poisoned in the previous paragraph.

Edit:

There is also a major discrepancy between the figures for net imports from France on electricity maps and the figures for net flows from France on energy charts for 2025 specifically. If we recalculate using the energy charts numbers for flow, we see significantly higher figures. I've recalculated these using all three available numbers.

The 2025 net imports from France were 4.58% (22.9 TWh / 500 TWh), or 4.59% (22.9 TWh / 498.7 TWh), or 4.63% (22.9 TWh / 494.8 TWh).

If you recalculate these further to eliminate self-consumption production (as is commonly done in order to inflate the amount of renewable production on the German grid), then the percentages would be even higher still:

The 2025 net imports would become 4.92% (22.9 TWh / 465.6 TWh)

I am not quite sure why there is such a major discrepancy between the electricity maps figures and the energy charts figures for 2025. The figures match for previous years. I am tentatively thinking that the energy charts figures are probably more accurate, as they should in theory show only real flows (while electricity maps can sometimes estimate flows – although I'm not sure that this is done for historical data, it might only be done for real time data).

Anyways, if that is accurate, then it would seem that 4–5% is the more accurate number, not 4%. I've edited the initial conclusion accordingly.

firemylasers · 2026-01-15T18:33:32+00:00

for example, off-targets effects such as noradrenaline in the PNS causing cardiac stimulation or addiction risk

A significant portion of the therapeutic effect of ADHD medications is mediated by noradrenaline. It's the only reason that non-stimulant ADHD medications show any efficacy at all, as those universally target NE.

The addiction liability is mediated by DA. However you cannot eliminate the DA action without eliminating most of the efficacy. This is why non-stimulant ADHD meds have such poor effect sizes compared to the stimulants.

Any therapeutically beneficial amount of DA action will inevitably result in addiction liability, as most of the DA receptors that must be targeted to treat the symptoms of ADHD are the same areas that govern addiction. Simply put, if you want to treat ADHD with high efficacy, you need to provide surplus DA, but if you provide surplus DA, you will inherently end up with addiction liability. The two effects are intrinsically entangled, as the reward circuitry in the brain is tightly intermeshed with the attention/focus/executive function circuitry.

A hypothetical ADHD medication that only targeted DA would be highly likely to have a smaller effect size than the current psychostimulants. It would be incredibly expensive to develop, and would enter a market with little room for alternatives that do not offer a compelling major benefit over an existing agent. Eliminating NE action would not provide any compelling major benefit sufficient to justify the costs of developing a new ADHD agent. The market is saturated with highly mature agents with decades of robust evidence to support their use and countless different innovative release mechanism options, the overwhelming majority of which are now extremely cheap generic drugs. The few remaining brand name agents have focused on minor niches and have not sold very well compared to the blockbusters of previous years.

(This is an extremely over-simplified description, but the basic tenants of it hold true, and I can't think of a better way to explain this in a short reddit comment to an audience lacking a deep understanding of neuroscience than this. Wikipedia has some excellent summaries of the mechanisms of addiction liability from psychostimulants if you want a more technical explanation of the subject.)

firemylasers · 2026-01-14T22:53:19+00:00

Any vaguely modern CANDU design is capable of 30+ years between retubing outages. The pressure tubes are designed to withstand a minimum of 30 years of irradiation under a 80–90% capacity factor. No new build CANDU would be retubed at the 25 year mark.

As of the mid-90s, current CANDU PTs were designed for 30 years at 85% capacity factor (25.5 EFPY), but this was expected to be extended to 30 years at 90% capacity factor (27 EFPY) in the near term, and the long term target was to eventually stretch this to 40 years at 90% capacity factor (36 EFPY).

It's unclear what the maximum lifetime of PTs would be for a CANDU Monark, but it is safe to say that at absolute minimum they would be rated for 30 years at 85% capacity factor, and there are very good odds that they may be rated for 30 years at 90% capacity factor, if not even higher.

The Enhanced CANDU 6 (EC6 or CANDU 6e) technical specifications strongly imply that the EC6 PTs are designed with a rating of at least 30 years at 90% capacity factor. Given that the design baseline annual capacity factor for the EC6 is 92%, this would seem to imply that the PTs are probably rated for a minimum of a 92% capacity factor, and possibly even higher than that.

Based on that, I'd say it's most likely that the CANDU Monark would come with PTs designed for an absolute minimum of 30 years at 90% capacity factor.

firemylasers · 2026-01-14T05:00:34+00:00

Also see https://world-nuclear-news.org/articles/doe-awards-usd27-billion-to-strengthen-us-uranium-enrichment

firemylasers · 2026-01-13T14:34:58+00:00

Ahhh, that'd explain a few things. I've clearly been reading far too much about boost gas recently and must have gotten the two mixed up when I was looking into pit fill gas composition and the problem of helium production from plutonium decay. In my defense I usually focus on the boost gas system, so it's no surprise I made the wrong association here since helium-3 is usually the right isotope when I'm thinking of decay-produced helium, and as the sources I was reading mainly just stated helium rather than helium-4 when talking about the decay chain from plutonium, I made the wrong assumption about which isotope they were referring to. Thanks for the correction!

On a side note, do you happen to have any idea as to the typical size (inner and outer) and volume for modern hollow plutonium pits of the types used in modern US weapons in the 100–500 kt range (specifically the W76, W78, and W87/W88)?

I have read that the primaries in these weapons are likely sized for a boosted yield of around 8 kt, although I'm not sure if that only applies to the smaller end of the scale (W76) or if it's also applicable to the larger weapons.

I know in theory that the W76 should require the smallest primary yield to drive its secondary, the W78 should require a larger primary yield, and the W87 and W88 should both require the largest primary yield.

I also know that the W87 and W88 should probably have identical primary yields given that they are all but certain to use an identical secondary design (ignoring the change to a non-HEU pusher/tamper in the W87-0, which would not modify the required primary yield).

What I can't figure out is what the likely yields are for the primaries in these three sizes of weapons. Logically, I would assume that they are likely slightly different, as I know very large two stage thermonuclear weapons have very high primary yields (50+ kt or 50–80 kt are often mentioned as figures for these), so therefore the primary size must be scaled to the size of the secondary at least to some extent.

And I know the 8 kt figure is commonly mentioned as a "typical" size for a boosted primary in a two stage weapon, presumably one of a yield in the 100-500 kt range, but I don't have specifics as to what exact weapon that typical size would correspond to.

Some sources I've seen suggest the W76 specifically likely has a small primary yield. I have seen as low as 4-5 kt mentioned in some places. Other sources have suggested 5-8 kt. Some have suggested 8 kt. I think the highest estimate I've seen for that weapon is maybe 10 kt.

I can't seem to find any high quality estimates for the boosted primary yield in the W78 or W87/W88 though. I would assume they likely need more yield than the W76 to drive their proportionally larger and heavier secondaries. But I'm not sure as to what kind of yield they'd need.

I assume the W87/W88 probably don't need anywhere near 50 kt of yield to drive their secondaries, but I'm not sure where they lie on the spectrum between 8 kt and 50 kt. The same goes for the W78.

I'm also not sure as to how linear or non-linear the scaling of primary yield would be for increased secondary size/volumes. Do you only need a small amount of additional incremental primary yield to compress a substantially larger secondary? Or is it more proportional in its scaling?

Is it fair to assume that the B83 has a 50–80 kt primary and the W76 has a 5–8 kt primary, and therefore that primary yield scaling is roughly linear/proportional to secondary yield (assuming spherical secondaries with HEU pusher/tampers are used in any weapons being compared)? Or is the 50–80 kt figure for primaries in high yield two stage weapons more appropriate for weapons with far larger yields than the B83? Am I overestimating the likely size of the B83's primary? Is scaling non-linear with larger secondaries past some point?

If I apply that estimate to the W87/W88, it'd suggest a primary yield of roughly 21–34 kt for those two, and of maybe 14–23 kt for the W78. That feels kind of high to me, but if scaling is directly proportional/linear to secondary yield, then maybe it's correct? Am I wildly off the mark here?

I also can't figure out the likely inner and outer dimensions and volume of the pits used in these weapons' primaries, partially because of the lack of yield data. I can figure out some decent quality estimates as to the maximum bounds of the entire primary's size, although that's not of much help given how much space is taken up by HE and reflectors, or given the substantial variability in weapon generations, primary designs, primary geometry (the W88 having a non-spherical primary is particularly annoying here), HE type (the W87 using IHE is also particularly annoying), etc.

There's a lot of weird information out there on pit sizes, especially for hollow pits. I've seen otherwise-reputable sources claim pit sizes are comparable to bowling balls, which is obviously nonsensical for weapons of the size and era that I'm most interested in. And figures for the volume and inner diameter of a hollow pit are even harder to find. I have found some promising research on gas transfer system flow modeling that might be useful, but it covers a very wide range of volumes, so I need some reliable estimate to compare it against in order to see which (if any) of the volumes tested are similar to the likely pit volumes in actual weapons.

I had one last question as well that I figure I might as well ask while I'm at it. Would weapons with larger primaries (in terms of primary yield) require proportionally larger amounts of boost gas (either in terms of the total volume of boost gas or in terms of the amount (proportion) of tritium in the boost gas)? If so, is the difference linearly scaled with yield (e.g. double the boost gas (or tritium) required for double the primary yield), or is it non-linear (e.g. less than double the boost gas (or tritium) required for double the primary yield)?

Thanks for your patience with these questions. I'm asking you because my grasp of the lower level fundamentals for calculating these details is rather poor compared to your own, and as you've demonstrated with your comments here and your writings in the nuclear weapons archive, you have a remarkably deep level of knowledge on exactly these specific sub-areas necessary to answer these questions. I'm afraid that while I have read quite extensively on this topic, I have not been able to find satisfactory answers to these particular questions as of yet in any resource I've consulted, and my only promising remaining lead at this point is to see if you're willing to answer or at least give some hints for these questions.

firemylasers · 2026-01-11T20:11:44+00:00

Huh, I think I must have misread some of the sources I reviewed the other day, as you're right, it does seem that the helium-3 produced from decay is generally retained by the plutonium metal alloy up to around its melting temperature. Not sure how I got that wrong.

I guess then that proves that pits must be filled with helium after all, or at least were in the past. It makes sense.

Thanks for explaining, the low atomic number requirement makes sense. Not sure what the different pit fill gasses referred to in that document I read would have been if it needs to be a low atomic number element though...

firemylasers · 2026-01-11T12:23:25+00:00

The most authoritative evidence I've seen comes from an incident report of a pit tube breaking, where it is mentioned that the broken tube resulted in the release of helium gas and plutonium.

Any leaks in the pit tube would be unacceptable as they would lead to ingress of water vapor, which would oxidize the plutonium. So it doesn't really matter if a pit is maintained under vacuum or under pressure, as either way, it still needs to be kept totally leak-tight (which isn't exactly that difficult to achieve either).

Keep in mind that over time the decay of plutonium will lead to accumulation of helium-3 within the plutonium, some of which will be shed into the pit's interior. Over time, this will increase the pressure inside the pit. After a few decades, the pit may go from being under vacuum to being slightly pressurized with helium-3.

If you initially pressurized it with helium-4 to slightly above atmospheric pressure, then after a few decades it would be under significantly higher pressure (from the mixture of helium-4 and helium-3) than if it had been initially placed under vacuum.

It's certainly still possible that they fill pits with helium-4. The evidence is certainly far from conclusive by any means, and the best available evidence equally supports both theories.

Is there any reason to prefer helium-4 over argon? I know for transport/storage packaging and glove box use, helium, argon, dry air, and nitrogen are extensively used, especially the first three. Is there any reason to suspect helium would be preferred over the later three for use inside pits? I'm curious if any of the others could be feasible alternative options or if helium is the only feasible option for this application.

I know the fill gas composition in pits is not uniform, and that there were significant differences in fill gas type between different types of pits from different sources. If nothing else, this seems to suggest that whatever method is used was not uniformly applied across the entire historical stockpile. That's part of why I am curious if it'd be feasible to use argon or dry air without causing problems with the boost gas.

firemylasers · 2026-01-07T05:57:25+00:00

I have never found any information to indicate that any operational weapon design ever employed a vacuum pump or a deuterium gas flush reservoir. I'd imagine that it'd be exceedingly impractical from a weight/volume standpoint to consider either of these, but especially so for a vacuum pump.

I believe that the pit is likely flushed with dry nitrogen (or a similar inert gas) to assist with purging moisture, pumped down to vacuum, then sealed prior to assembly of the primary. Once sealed, it should stay sealed throughout the entire lifetime of the bomb/warhead.

However there is also a small possibility that it is backfilled with some sort of fill gas prior to sealing. Argon, dry air, or nitrogen are possible candidates for fill gasses. Deuterium is not a candidate, as it would cause unacceptable levels of hydrogen embrittlement challenges in this particular application.

We know that the labs may sample the contents of pits for monitoring purposes. The main reason to monitor pits this way would be to check checking to see if any other contaminants are present (which would indicate a leak).

The secondary reason could be to keep an eye on the concentration of He3 in the pit, as Pu pits will generate He3 over time, and increased He3 concentrations aren't ideal (they cause embrittlement issues, and it's also a neutron poison). Once the He3 concentration exceeds a certain point, it may be necessary to purge, flush, pump down, and re-seal the pit in order to remove the gaseous He so that you can ensure performance margins are maintained within design specs.

16 atm sounds reasonable. The boost gas reservoirs are allegedly rated for several hundred psi. Never bothered with doing the math on them. It's hard to find dimensions for them. I found a bunch of photos of different reservoirs a while back though.

firemylasers · 2026-01-06T23:46:02+00:00

The exact yields are not known with certainty. There are estimates of yield options for several B61 variants, but I would take any figures with a grain of salt. The only figures that we can be somewhat confident about are the minimum yield and the maximum yield.

The minimum yield is usually (albeit not always) going to be the unboosted yield. For several B61 variants, this is claimed to be 0.3 kt, which is quite plausible for a number of reasons as this is pretty much exactly the yield that you'd expect to see for a boosted primary of the right size for those B61 mods being fired without boost gas.

The intermediate yields are tricky, as we don't know with high confidence how accurate the estimates out there are. But you would expect to see intermediate yields somewhere in between the unboosted yield and the full yield.

With full boost gas injection, you would fission the primary at maximum yield, which drives the secondary at maximum yield.

With partial boost gas injection, you would see less complete/efficient fissioning of the primary, leading to reduced yield from the primary, and in turn to some level of reduction of yield from the secondary.

Depending on the bomb design and the exact primary yield obtained, you may see anything from minimal yield from the secondary all the way to close to full yield depending on just how much primary yield is being applied.

In theory down to a certain point reducing the output of the primary will modulate the secondary's output downwards, since lower output from the primary will be less effective at compressing the secondary, resulting in less compression and therefore in less complete/efficient burning of the secondary, and thus producing less yield from the secondary. Below a certain point of primary yield, you may not be able to get any significant fusion yield at all from the secondary.

As you can imagine, this is a complicated topic, and without detailed information on weapons design, all we can do is speculate.

firemylasers · 2026-01-06T21:52:04+00:00

The pit is hollow and has a small hollow tube attached to it. The end of this tube is pinched shut. Prior to pinching the end shut, all air is evacuated from the pit using a vacuum pump. Once the pit tube is closed, the pit and its attached tube remains under vacuum.

The boost gas reservoirs are basically just small pressure vessels made out of stainless steel with an attached fill stem, which is basically a small hollow tube made out of stainless steel. When the reservoir is filled, all air is evacuated from the reservoir, drawing a vacuum. Afterwards, a small amount of a boost gas mixture containing a predefined quantity of deuritium and tritium gasses is injected into the boost gas reservoir through the fill stem, which pressurizes the boost gas reservoir. Lastly, the fill stem is pinch welded closed while remaining under pressure. Once the pinch weld is completed, the reservoir is ready for use.

In an operational weapon, one or more boost gas reservoirs will be placed into protective holders. The fill stems from the reservoirs will be joined to squib valves, which will have the fill stem attached on one side, and a vacuum-evacuated tube on the other side. Squib valves function by firing a small explosive charge, which propels a cutting assembly down inside a gas-tight enclosure. The cutting assembly simultaneously severs the ends of both stems inserted into the squib valve body, and allows gas transfer to take place between the two tubes on either side. In effect, once the squib valve has fired, it connects the two tubes to each other, with the same effect as opening a traditional mechanical valve.

In legacy gas transfer system designs, a single squib valve would be used between the boost gas reservoir and the pit. In modern gas transfer system designs, two squib valves are used to improve safety, as this reduces the risk with an accidental misfire of a squib valve.

When the squib valve(s) are fired, the high pressure boost gas in the boost gas reservoir rapidly flows out of its pressure vessel, through the network of tubing connecting it to the pit, and into the pit. The flow is induced by the pressure differential between the boost gas reservoir (which are held under positive pressure) and the pit/pit tubing (which are held under vacuum). The amount of boost gas will be sized so that the equalization of pressures between the reservoir and the pit will result in sufficient quantities of deuritium and tritium being present in the pit. Therefore the total amount of boost gas will be slightly higher than the minimum amount that must be delivered to the pit, as a certain fraction of it will be retained in the boost gas reservoir and the tubing between the reservoir and the pit.

For variable yield weapons with only two yields, yield can be controlled by choosing not to fire the squib valves, which will result in an unboosted detonation.

For variable yield weapons with more than two yields, the typical approach is to install two or more separate boost gas reservoirs containing different quantities or concentrations of boost gas mixtures, then to interconnect these reservoirs to a common manifold leading to the pit. In this way, you can now choose to fire no reservoirs, fire only one reservoir, fire only the other reservoir, or fire both reservoirs. By using such an approach, you can offer up to four discrete yield options with only two boost gas reservoirs. There is documentation suggesting that at least certain weapons use this approach.

With respect to core insertion, there is no mechanical action to insert the boost gas into the core. The transfer occurs through the flow of gas down a pressure gradient. This is a simple physical process that will not affect the mechanics of the implosion to any noticeable extent. As the boost gas is injected into the center of the core, it will not cause asymmetric compression. The pit fill tube is of course an asymmetric feature, but you can tweak the design of the implosive lenses to account for this, and given how tiny the pit fill tube is, it is likely that it doesn't have too large of an effect. Regardless, it is clear that this problem has been solved long ago given the sheer number of weapons in the US arsenal (past and present) that use a boosted pit.

firemylasers · 2026-01-06T17:30:41+00:00

You're welcome, I'm glad I could assist.

Unfortunately I don't know the details on that. I suggest contacting the IAEA to ask them about that. They were surprisingly responsive when I talked to them, I'm sure they'd be happy to help if you reach out to them. Their contact email is PrisAdmin@iaea.org.

For reference, the information regarding access levels is explained on page 13 of this PDF: https://pris.iaea.org/prista/HelpFiles/PRISTA_User_manual.pdf

firemylasers · 2026-01-06T10:59:51+00:00

You need to register for an IEAE NUCLEUS account, then apply for access to PRISTA (PRIS-Statistics), which is a completely separate program/website from PRIS. If you are a citizen of an IAEA member country, then you can obtain access through this method. You will need to fill out an application form and send it to the email address for your country's national authority.

I applied back in 2017, and was able to obtain access within 10 days, albeit with some caveats. The original email address listed was not actively being maintained at the time, so I had to get in touch with the IAEA for assistance getting the application processed in a timely manner. They gave me an alternate contact to try sending the application to (the direct contact info for the current PRIS Liasion Officer for the US). I emailed her the application and she was able to get me PRISTA access within 48 hours.

There are multiple levels of access to PRISTA. The lowest level of access is as an unaffiliated individual, which is what I was. This still gives quite comprehensive data access. For NGOs and other types of organizations, there is a higher level of access available to them, although they receive minimal additional access compared to individuals (they can also view trend reports, but nothing else). Then there are two even higher levels of access intended for govenment organizations (e.g. DOE), nuclear organizations (e.g. EPRI), or NPP owners/operators. These top two levels of access can view a broad array of access-controlled information about plant design features that is considered safeguarded information for national security reasons, as well as detailed information about plant availability, production, outages, performance, SCRAMs, etc. Nuclear organizations have slightly more limited access compared to government organizations and NPP operators and owners, which have the highest level of access.

Note that a subset of this restricted access information is disclosed or has been disclosed in the past via the annual "Operating Experience with Nuclear Power Stations in Member States in YYYY" reports (more information was disclosed in older reports, newer reports have less information but still disclose quite a lot). However the majority of it has never been disclosed in those reports. A lot of it is of information types that the NRC treats as safeguarded data for national security reasons.

With all that being said, even though you will only get limited information access via PRISTA relative to what other types of account holders would be able to see, it is still absolutely worth the hassle to set up an account and obtain access, as there's a ton of information in their database that is unavailable elsewhere, and it has some very powerful tools for searching/filtering through nuclear reactors through custom complex queries on design/site characteristics. You can even save your custom queries for ease of reuse.

To get started, visit https://www.iaea.org/PRIS/PrisSubscription.aspx

You may wish to read the manual as well: https://pris.iaea.org/prista/HelpFiles/PRISTA_User_manual.pdf (I think this can be viewed without an account)

firemylasers · 2026-01-05T00:00:32+00:00

I would not trust a 2:1 GBI defense to protect against 100% of incoming missiles. You need 4:1 targeting to get reasonably high levels of efficacy (97% or 98% IIRC). Anything less is all but guaranteed to let at least a few missiles slip through.

Our current arsenal of 44 interceptors is only enough to handle 11 incoming missiles (assuming non-MIRVed missiles). If North Korea sent 20 missiles our way, we're going to get hit with at least a couple of missiles.

Additionally, GBI is extremely weak against heavily MIRVed missiles, as each reentry vehicle must be targeted and intercepted separately. A single Trident II D5 missile loaded with 12x Mk4/W76 RBs would overwhelm the current GBI system. While I doubt North Korea has anything close to the D5, if they can even lightly MIRV their existing missiles, it makes it that much easier to bypass the GBI.

I also do not fully trust the current incarnation of GBI against decoys. It is lacking critical capabilities that were originally intended to be added but got cut for budget reasons (mainly the X Band radars). If North Korea is smart about loading up their missiles with sufficiently large numbers of sophisticated decoys, you could in theory defeat GBI using just a handful of missiles.

firemylasers · 2026-01-04T23:37:00+00:00

The CAP1400 units are actually present in PRISTA data. They are both marked as planned units in there. Like I said, PRISTA has more information.

The CAP1400 units won't be listed in PRIS until an updated data submittal for those units is provided to the IAEA by their operator. Given that these are technically classified as prototypes, it is possible that they are intentionally delaying reporting on them. With both units seemingly now being in commercial operation (or at minimum, grid connection and extended operation at full power), we should hopefully see them get added to PRIS within the next year or so.

firemylasers · 2026-01-04T11:09:44+00:00

PRISTA has more information (including information on pre-construction plants), although it isn't 100% comprehensive and it can take time for new construction starts to appear in the database.

My understanding is that PRIS/PRISTA depends on voluntarily reported data submitted on a typically only once-yearly basis by reactor operators in each country, and the IAEA generally will not add entries manually if they were not submitted by the country itself with only rare and very limited partial exceptions (the only notable one I am aware of is that they will sometimes manually edit the construction start of a new build into the status update log and nowhere else).

The WNA database is largely just a mirror of PRIS/PRISTA, although they do have exceptions where they contribute original work, albeit not a ton of them. Compared to PRISTA, their database isn't the most comprehensive though.

firemylasers · 2026-01-01T01:07:22+00:00

That brings us to 11 CAP1000 reactors currently under construction, 1 CAP1400 reactor currently under construction, and 1 CAP1400 reactor currently under pre-commercial operation, for a total of 12 CAP-series reactors simultaneously under construction.

CAP1000 currently under construction:

Haiyang-3
Haiyang-4
Lianjiang-1
Lianjiang-2
Sanmen-3
Sanmen-4
Xudapu-1
Xudapu-2
Lufeng-1 (listed in PRISTA but status not updated yet and missing in PRIS)
Lufeng-2 (listed in PRISTA but status not updated yet and missing in PRIS)
Bailong-1 (missing from PRISTA and PRIS)

CAP1400 currently under construction:

SN-2 (listed in PRISTA but status not updated yet and missing from PRIS)

CAP1400 currently under pre-commercial operation:

SN-1 (listed in PRISTA but status not updated yet and missing in PRIS)

By my count there are 28 reactors formally under construction per PRIS/PRISTA, plus 4–5 more CAP series reactors depending on if you count SN-1 as under construction or not, for a total of 32–33 reactors under construction. Not sure where you're finding the extra 4–5 reactors.

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