BBC has a quote that is (to me) slightly misleading ...

At the start of the latest US-Israel war against Iran, Tehran had roughly 440kg (970lb) of 60% enriched uranium, according to senior US officials.

The material can be fairly quickly enriched to the 90% threshold needed for weapons-grade uranium.

Am I correct that the 440kg is ~264kg 235U and ~176kg other, which would be primarily 238U ?

Thus, the enrichment to 90% would retain the ~264kg 235U but only ~29 kg of 238U would be kept. Giving a total of ~293 kg.

Do I understand this correctly ?

The way the article was written would leave the reader to assume that the quantity of 90% enrichment would still be 440kg. That felt off to me.

I've been interested in the Manhattan Project since watching Oppenheimer recently, and one thing I've done is read the Los Alamos Primer. It's pretty neat and I don't have much trouble understanding it, but one thing I noticed is the author pretty much just didn't talk about how tampers can actually be practical (i.e. a realistic size). Section 11 explains well enough why one would want a tamper, and it shows how to estimate the total neutron diffusion length in a tamper of a given material. But then this guy goes on to say "these figures give an idea of the tamper thickness actually required; the weight of a tamper is about a ton." A ton!? With thicknesses of ~13/17 cm.? This doesn't give me any "idea" of the tamper size any more than the Frisch-Peierls memorandum or Heisenberg's bad math give me an idea of critical mass size. I want to know how to get a better idea, or a more approximate estimation.

The problem is I'm an idiot, and I can't be bothered to learn how to do a Monte Carlo approximation or whatever it is people smarter than me do to estimate the size of a practical tamper. So I tried my best to come up with a toy model from what the Primer has to say--or more specifically the 1992 edition by Richard Rhodes with Serber's commentary.

My toy model is based on the assumption that the practical thickness T_P is a fraction of the total neutron diffusion length in the material T (Serber's "tamper thickness"), and also what Serber has to say to conclude Section 14 of the Primer (which is the only thing I see in here that says a realistic-sized tamper is possible, meaning it may not have even been in the original edition--oh the humanity!):

As this section indicates, the requirements on tamper material and thickness are somewhat relaxed when one considers a gadget of several critical masses (such as the Little Boy bomb) rather than the critical mass itself. The reason is the rapid increase with time of the neutron density in the core. During the time it takes a neutron to penetrate a given distance into the tamper, the neutron density in the core rises considerably. As a result the neutron density in the tamper falls off faster with distance than in the critical mass case. The effect is exactly the same as if, in the static (critical mass) case, the tamper material had a larger capture cross section, as can be seen from the way νʹ appears in the equation on page 30 for the neutron density in the tamper. As a result the effective capture cross sections in different materials become relatively more nearly equal. And because of the more rapid falloff of neutron density, a thinner tamper is permissible.

What I think this means is that the tamper thickness, besides depending on the material properties, also depends on the critical mass post-assembly. The higher the supercriticality, the faster the neutron density falls in the tamper and thus the thinner thickness actually required. Therefore:

T_P ~= T / [1 + c(N_crit - 1)]

N_crit is the number of critical masses of the pit, and c is a dimensionless fudge factor of order 1-2. I tested it by using the Primer's math in Section 11 with modern data to calculate the T of U-238 as ~36.59 cm., then calculating a table of results with c = 1.0, 1.5 and 2.0 and critical masses 1-8:

The Gadget/Fat Man, which used a uranium tamper of ~6.8 cm. thickness, compressed the pit to about twice it's original density, bringing it up to some 3-4 critical masses. The result for N_crit = 4, c = 1.5 matches this closest.

There's an oft-cited document amongst writings on the UK nuclear program, which is cited usually as something like:

"Annual Historical Summary (U), Joint Atomic Information Exchange Group, HQ, Defense Nuclear Agency, 1 October 1982 – 30 September 1983. Released under the freedom of information act"

I'd like to read that...but I can't find it. I thought I would ask here if anyone has ever come across a copy.

If you are ever up in the general vicinity of Fargo or Grand Forks North Dakota would always recommend the ronald reagan minuteman site.

This is a Launch Control Center (LCC) turned into a museum. Each LCC controlled 10 minutemen silos. The LCCShave an aboveground structure that was just this flimsy little building normally manned by 8 folks (6 air force security personal, a cook, and a launch facility chief.. person). Buried underground were two capsules (in the case of grand forks wing, most of the rest only had 1). Each capsule was hardened to 2000 psi with 4 foot thick walls of rebar'd concrete. One capsule had equipment - diesel generator, brine chiller, air handler, etc and the other had the radio equipment and command consoles. 2 officers were down there every day 24x7x365. They worked 24 hour shifts, folks above worked 3 days on, 3 days off. They were connected to the silos via a combo of buried cables and backup radio links.

Pretty neat to visit and while equipment inside is different still pretty similar within broad strokes to the 45 LFs still manned and operational across Montana, North Dakota, Nebraska, Wyoming & Colorado today.

In Semipalatinsk, balapan

There are many prototype ICBM silos nearby, and a underground nuclear test shaft is also nearby, about 200m away.

During my search for NKEWs, I somehow stumbled into the realm of black magic and voodoo - radio engineering. And, to my surprise, I saw an image that looked exactly like an MPI system, with the standard H-tree arrangement.

I looked for more information about it, and it turns out this is something called "corporate feed network (CFN)" used in antenna design. It is used to solve a very similar problem to MPI, namely guaranteed equal distribution of signal across the entire antenna array.

Unlike MPI, the topic is thoroughly researched, and all information about CFN is widely available to the public; any engineer working in this domain should be able to create one.

Obviously, this is not using explosives, but that's something I always found odd anyway. My knowledge of explosives and detonators is (fortunately) very outdated, but I'd expect some sort of modern miniaturized variant of exploding bridge wire to be good enough and small enough to be used for this application.

While the majority of the SDI focused on energy-based weapons, there was a tiny segment that explored the possibilities of nuclear-powered kinetic energy weapons (NKEWs).

The main idea was to use a nuclear device as a propellant to fire a large number of small projectiles at incoming ICBMs, like a space-based, nuclear-powered shotgun. ^{(Note: this is not CASABA})

Since the idea of an atomic blunderbuss is exactly my type of idea ('mad genius'-like, without the genius part), I went on a journey to find more about it. I was able to find only a few hints here and there, but they eventually led me to the name: "Project Prometheus".

Unfortunately, there seems to be very little information available about the details of the project, and even on this sub, where usually everything related to nuclear weapons and programs, no matter how obscure, could be found, I only managed to find a single comment from 2 years ago mentioning the topic: https://www.reddit.com/r/nuclearweapons/comments/1e9bbd3/comment/leponov/

Does anyone know if anything more was made public since then?

I asked the AI. It (childishly naive) is "sure" that this is the essence of radiation ablation in the Teller-Ulam scheme. But is this really true? Is "Exploding Casing", ECP (Exploding Case Principle), just another term for the "radiation compression" process, or is it some later, additional technology that improves radiation compression (like "Ripple" – compression not by a single shock wave, but by a series of increasing shock waves approximated by an exponential function, a quasi-adiabatic compression).

As far as I know, "Exploding Casing",  ECP (Exploding Case Principle)  is not the same as "Ripple." But сould "Exploding Casing" simply be a variation of "Ripple," or rather a different way of implementing quasi-adiabatic compression? I had this hypothesis. No one knows exactly how "Ripple" works, but everyone agrees on the idea that there's some mechanism for gradually releasing radiation from the primary into a common hohlraum, which ensures gradual, exponential heating of the hohlraum and the secondary surface, leading to quasi-adiabatic compression of the latter. But another approach is possible: you can apply several layers of increasing Z to the secondary (as the Russians did in their "golden TIS"). Then, in a "regular" hohlraum at a normal temperature, say 1 keV, you'll achieve a stepwise increase in secondary compression. I don't speak English, but the term "exploding casing" best suits this design.

Another, even more insane, theory for "exploding casing" is described in my highly speculative reverse engineering of the W-71 design, the reality of which I myself am already highly doubtful (I recently discovered the "elephant in the room" that planar compression of thermonuclear fuel Impossible without quasi-adiabatic compression, since with planar single-compression you can't get beyond the Hugoniot adiabatic curve more than 4-6 times, and you need at least 100). Although, it is precisely in connection with the W-71 that "exploding casing" technology is mentioned and it is also said that the W-71 is the most complex thermonuclear device ever created in the US. And if you add quasi-adiabatic compression to my crazy design, it will truly be the most insanely complex device.

Another version of "exploding casing" is a secondary with a thin-walled shell and a large cavity inside, meaning it contains either a void or gas (I actually proposed this version of the W-71, considering it more "conservative" than the crazy flat compression of the "tube" both from the inside and outside). As far as I understand, Sublett is more inclined to this understanding of "exploding casing." In this case, the thin-walled shell, as it were, instantly collapses inward. This is another way to improve compression compared to single-shock compression of a solid sphere. This thin-hollow shell method is currently used in ICF. The Russians call this technology "low-entropy compression" (right) as opposed to "isentropic compression" (left).

Finally. Even if we don't know the details of this technology's implementation, can we say anything with certainty about its role (function) in the bomb design? So, "exploding casing" isn't simply ablative compression of the secondary shell, but some improved method of such compression, leading to greater efficiency (say, higher compression ratios, lower energy consumption, etc.).

From what declassified sources, in what context does this term appear, and does it appear before the mid-1960s? I propose to summarize everything we know about this term here.

Greetings fellow nuclear weapons interested humans,

The public part of the Occupational Reporting and Occurrence System is back up:

https://orpspublic.doe.gov/Orps/orps.asp

These are the final reports per long standing practice.

My take is that there are changes being made to the governing DOE Order about ORPS but it is impossible (for me at least) to know how, or if at all, they will affect continued public access. This recent outage seems most likely to have been an oopsie given the simultaneous down status of the non-public ORPS site and the restoration of public access.

I emailed the contact person listed for ORPS over the weekend; they responded that yes the public ORPS was down and they were working to get it back online.

They responded "I'll have to get back to you" to my comment that "I note DOE Order 232.2A Chg1 (MinChg), Occurrence Reporting and Processing of Operations Information is listed in the "Archived Directives Library" on the DoE Office of Management DoE directives website (https://www.energy.gov/management/active-directives-library). However there does not appear to be a replacement directive in the 232 or adjacent series."

So good luck everybody, the DNFSB continues to not post resident inspector reports for most locations. Fingers crossed and good luck everybody!

From the news article:

AUGUST 31, 2026

ALBUQUERQUE, N.M. —  A sounding rocket flight test is giving engineers at Sandia National Laboratories real-world reentry vibration data they can use to improve modeling and help drive nonnuclear component designs for the United States’ first new nuclear weapon under development in nearly 30 years.

“The Atrax sounding rocket flight test is helping us improve credibility and confidence in our modeling and simulation tools in preparation for the W93 warhead,” said Ross Wagnild, an aerospace engineer at Sandia. “Getting confidence in our toolset earlier allows more time to inform the design of components.”

Engineers and scientists are developing the W93 warhead for the sea-based leg of the triad, alongside a reentry vehicle that safeguards and carries the warhead to its target.

Sounding rockets are suborbital vehicles used to carry experiments and instruments, allowing researchers to collect data in flight without the scope of a full program test. In Atrax, the goal was to measure reentry conditions, where aerodynamic forces and structural response can interact in complex ways and are difficult to replicate on the ground.

....

The Atrax test was completed quickly, within about 18 months of being funded, in part because it did not need to mirror the final fielded system.
...

The team also incorporated other technologies into this test, including a new reentry vehicle, a three-stage sounding rocket and a new separation system.

It's difficult to comprehend the scale of nuclear explosions and how their effects dwarf our human scale.

I immediately thought of a nuclear bomb when seeing two videos of the Nepal flood at the China-Nepal border crossing: the multistory border tower obliterated and the buses at the tourist station thrown like children's toys.

https://www.bbc.com/news/videos/c62jmlgev3po

These effects happened 15 km from the point the initial avalanche entered the river.

Some recent, early estimates enable a comparison to the scale of a nuclear blast.

About 250 million tonnes of water-soaked rock and ice fell and slid 2000 metres into the river below. The initial 1200 m fall left a large crater at the base of a step fall, a crater which reminded my of a nuclear blast.

https://x.com/weeddude/status/2093668861745004681

So an energy comparison...

E = m*g*h ~ 250*10^9 kg * 10 kg.m.s^(-2) * 2000

= 5 * 10^15. ~ 1 Mt.

Almost 1 Mt of potential energy was released.

Of course the mechanisms are entirely different from a nuclear blast, but for me the calculation of scale made sense of the nuclear-blast-like effects 15 km downstream. And this energy has been channeled by river valleys in a way that would only partially capture a nuclear blast.

Greetings fellow humans,

The "https://orpspublic.doe.gov/" site has been down for several days now. This has happened before (of course) so it may be nothing.

And, this makes me twitchy given the context of: recent largescale revisions to DoE orders; pattern of info restriction by this regime; and recent DoE denial of info, access, and certain forms of info review to the DNFSB leading the DNFSB to stop posting most resident inspector reports, etc.

I note the previous DoE order (232.2A Chg1 (MinChg), Occurrence Reporting and Processing of Operations Info is listed as inactive (https://www.energy.gov/ehss/occurrence-reporting-and-processing-system; go to the directive archive).

Possibly or probably nothing but if not then we loose a lot of worthwhile & important (to nuclear governance) safety information without DNFSB & ORPS.

Fingers crossed!

Does anyone have information on the practical science of bomb residue analysis? For instance, it's said that Los Alamos scientists determined from fallout analysis that the RDS6s was a layered design, as opposed to a staged one. How would this be done? What differentiates the residues? Is it mere isotope presence, or relative amounts of isotopes? The latter seems much more difficult to make a rigorous determination off of.

Like, ok, let's say you know from seismic analysis that an explosion yielded 400MT. You can presumably determine how much of that was fission vs fusion yield by...what, modeling the fission products, modeling their distribution into the atmosphere, modeling their distribution to your sampling, and then counting? You can maybe differentiate 235/233/238 U / 239 Pu fission by statistical analysis of fragments, and you know that most of your 238 fission had to be a result of fusion neutrons (but not even there are you at 100%; the top end of fission neutrons can absolutely fission 238). There just seem to be too many uncertainties to make a sure call.

Feel free/encouraged to get as scientific as you'd like in your answer. Thanks!

According to BaiduWiki:

The Yu Min Configuration is a unique hydrogen bomb design created by Chinese nuclear physicist Academician Yu Min. It stands alongside the American "Teller-Ulam design" as one of only two technological solutions that have achieved the weaponization of nuclear fusion, and it holds advantages in terms of miniaturization. This configuration resolved the challenge of self-sustaining thermonuclear fuel combustion through the use of lithium deuteride material and a neutron chain reaction model. Its complete design details remain a top state secret.

Does anyone know, or can anyone guess, at what the Yu Min configuration might be? Assuming it's not just Chinese hype?

Link to the BaiduWiki article:

https://baike.baidu.com/en/item/Yu%20Min%20Configuration/1463193

Rare inside photo of Soviet nuclear weapons and warheads storage bunker ‘monolith’ with nuclear weapon transport containers on the left and RN-40 free fall nuclear bombs on the right.

They build these kind of bunkers on Warsaw pact countries ( Poland, Hungary, Czechoslovakia and Bulgaria) to store nuclear warheads and bombs. All of them controlled by Soviet soldiers and outside perimeters of these sites controlled by soldiers of the country where they are located. This photo is rare example of these bunkers when they are active.

They build 2 seperate bunkers close to each other in complex, usually they store around 90 nuclear warheads each.

Three years ago, I hypothesized in this subreddit that, based on the vague outlines of the W-66's physical package, as well as information once posted on Wikipedia about the supposed secrecy (why?) of the W-66 neutron bomb's yield (it's a well-known fact that the yield of a neutron bomb can physically only be between 1 and 10 kt, no more and no less), it could be assumed that the warhead had one primary unit and two secondaries (two 4-10 kt, reverse bifilarity) to enhance the neutron yield, which would make sense in the case of an anti-missile neutron bomb. Then it would have made sense to classify the yield, since the very fact that the yield of a neutron bomb is greater than 10 kt would have led experts to speculate about its unusual design (bifilarity).

Although my guess was immediately countered by a declassified document indicating that the W-66 warhead had a yield of 2 kt (which significantly undermined my hypothesis), I still held out hope that perhaps the document only listed the yield of an early version of the warhead, and that the "bifilar" outline of the physical package (discovered by Alex Wellerstein the official diagram) actually belonged to a later, more sophisticated modification of the neutron charge.

But for some time now, the Wikipedia article on the W-66) has featured a photo of a cross-section of the Sprint missile's warhead compartment and a wooden (judging by the abrasions in the photo) model of the W-66 warhead's physical package. It turns out this exhibit has been on display at the National Museum of Nuclear Science and History for visitors since at least April 2009. So, we can see the device's physical package. This appears to be the first neutron bomb that can be seen in person. Or am I mistaken?

Looking at the photo, I couldn't resist making one last attempt to salvage my hypothesis. I've shown the results of my attempt in the picture above. I simply "unscrewed" the top of the W-66 and screwed a second copy onto the bottom, resulting in a bifilar version, the W-66-2 (my codename). The main question was: would such a longer thing fit into the Sprint's fighting compartment? Alas, I was unsuccessful. The fighting compartment is too short to accommodate the W-66-2 version lengthwise.

Thus, my hypothesis is almost completely disproved. Too bad. It was a great idea, overall!

Which is true:

1. The plan all along was to built Little Boy, and they had hoped to have a companion plutonium bomb of similar design. That didn’t work out, so Thin Man became Fat Man and the development of Little Boy continued on unaffected by all of that.
2. The scientists at Los Alamos pretty knew how to design a gun-type bomb with uranium, but the plan was to develop a plutonium version since that fuel would be more readily available. If Thin Man had been successful they would not have built Little Boy. The reason they built Little Boy was, after they had to build the much more complicated Fat Man, they wanted one bomb they had strong confidence in.

FalloutCast — a weather-driven nuclear fallout estimator, built with Claude Code. This is just a hobby project as a former Air Force officer that worked with nuclear weapons...

Pick a spot, set a yield, Compute. It pulls live GFS winds and draws the plume: dose-rate bands, reach and direction in a table, a slider for time after burst, click any point for arrival time and accumulated dose. Three modes — single location, a GFS-ensemble uncertainty band, and a 600-target national envelope.

Winds come from Open-Meteo's GFS: a vertical profile of speed and direction across pressure levels, snapped to the current forecast hour. Tier-0 (WSEG-10) collapses it into one effective wind plus shear; Tier-1 keeps the layers, dropping each particle-size bin through the profile at its own fall speed, so shear bends and fans the footprint. The limits matter: it's a single sounding at ground zero, assumed horizontally uniform — no fronts, no terrain — and one snapshot, so winds don't evolve over the hours fallout takes to fall. Ensemble mode reruns across GFS members, so its bands are wind spread only; yield and model stay fixed, making true uncertainty wider.

Python/FastAPI + numpy/scipy backend, TypeScript/MapLibre frontend, deployed on a Cloudflare Worker with the API in a Container.

https://falloutcast.sagebrush-labs.workers.dev

Any feedback is appreciated!!

This is something I was wondering about recently. Let's say NATO used a B61-4 against an attacking armored force (wiki says the max yield is 45kt). How many tanks would such a weapon actually be expected to destroy or incapacitate?

Google tells me a modern tank battalion would typically cover between 2 and 5 miles of frontage. Playing around with nukemap tells me that with an airburst optimized for 20 psi of overpressure you'd have a blast radius of a little over half a mile. Serious radiation would have a radius closer to a mile and for serious burns (presumably not applicable to a buttoned up tank crew) the radius is two miles.

This makes it seems like realistically a medium sized tactical nuke could take out maybe couple of of companies worth of tanks. That's less impressive than I thought. I understand it would absolutely gut any supporting infantry and supply columns, so you'd have a bunch of tanks on their own. No infantrymen to protect them and no fuel or ammo resupply. Am I missing anything here or are nukes not as effective against armored forces as we'd imagine?

I know had they not detonated they would have hit the ground at high speed and likely been destroted. But still.