Plausibility Check: 580 kg HEU Goes Loose from Ulba, Kazakhstan

[Workable Goblin]

A nuke that can only demolish 200' for steel latticework, the equivalent of a construction crane, probably won't match the damage done in 9/11.

No, it would probably be quite a bit worse...less in raw blast damage and more in the ZOMG, radiation! aspects, admittedly, but still.

My reference point for the degree of damage this can cause is the Oklahoma City bombing, which was the equivalent of a 5 ton device; the 1998 embassy bombings, which had an explosive power no greater than 20 tons; and the 1983 Beirut barracks bombing, which had a yield of about 10 tons. Comparing to those, detonating a 200-ton yield device in a large downtown area would likely cause hundreds of deaths and thousands of other casualties, mass panic, and, in general, an enormous impact. It would absolutely be among the worst terrorist attacks ever (9/11 is a huge outlier here, with 4 times the deaths of the next most significant terrorist incident).

If you managed to locate fissile material and gather the resources to turn this into a working nuclear weapon that is your only chance for this to occur would you be satisfied with 200t? I sure as hell wouldn't.

The point is that even a device that "fizzles" is still going to do a huge amount of damage and cause mass hysteria and panic, even before people figure out it was a small nuclear weapon and not a large conventional bomb. Any terrorist organization would be pleased with that, even if they were also disappointed it wasn't bigger.

 

[Andras]

Reactor grade fuel doesn't have as high a % U235 as weapons grade fissionables. While is possible to fission 20% using a very large implosion design, it's not practical at all. You'd still need to get it to about 80% before it's really usable in a crude fission device. 40-50% is usable as a second stage w a Pu core.

 

[Delta Force]

Reactor grade fuel doesn't have as high a % U235 as weapons grade fissionables. While is possible to fission 20% using a very large implosion design, it's not practical at all. You'd still need to get it to about 80% before it's really usable in a crude fission device. 40-50% is usable as a second stage w a Pu core.

Military nuclear reactor fuel is usually enriched to weapons grade. Some civilian reactors also run (or ran) on highly enriched weapons grade fuel, including plutonium, although they are being converted to run on lower grade fuel due to proliferation and terrorism concerns.

 

[Andras]

Military nuclear reactor fuel is usually enriched to weapons grade. Some civilian reactors also run (or ran) on highly enriched weapons grade fuel, including plutonium, although they are being converted to run on lower grade fuel due to proliferation and terrorism concerns.

Naval reactors appear to run around 50%, and they are the highest grade for reactor power. Basic weapons grade is 80%, and higher is better. A crude device will not work on reactor grade fuel. 40-50% only works if it is the secondary stage with a PU core.

 

[Delta Force]

Naval reactors appear to run around 50%, and they are the highest grade for reactor power. Basic weapons grade is 80%, and higher is better. A crude device will not work on reactor grade fuel. 40-50% only works if it is the secondary stage with a PU core.

The Alfa class is thought to have used fuel enriched to 90%, or weapons grade. However, the Soviet Navy used various types of fuel compositions. Most used were composed of a mix of uranium and aluminum and would have required chemical separation to yield usable material, although some were composed of uranium oxide, which is directly usable in a nuclear weapon. The November class submarines used fuel enriched to 90% as well. The link mentions that a naval base continued to receive shipments of fuel for first generation nuclear submarines well after the retirement of those submarines and the collapse of the Soviet Union.

However, it's true that most naval nuclear reactors do not run on highly enriched fuel. Only the USN typically does. The PRC and France prefer low enriched fuel, while the Soviet Union/Russia typically use fuel enriched below weapons grade.

 

[BlueTrousers]

No, it would probably be quite a bit worse...less in raw blast damage and more in the ZOMG, radiation! aspects, admittedly, but still.

My reference point for the degree of damage this can cause is the Oklahoma City bombing, which was the equivalent of a 5 ton device; the 1998 embassy bombings, which had an explosive power no greater than 20 tons; and the 1983 Beirut barracks bombing, which had a yield of about 10 tons. Comparing to those, detonating a 200-ton yield device in a large downtown area would likely cause hundreds of deaths and thousands of other casualties, mass panic, and, in general, an enormous impact. It would absolutely be among the worst terrorist attacks ever (9/11 is a huge outlier here, with 4 times the deaths of the next most significant terrorist incident).

According to NUKEMAP, even a 0.2 kiloton yield at the World Trade Center's South Tower would kill more than 22,000 people and injure another 18,000 people, and collapse several buildings including both towers, without even considering the effects of fallout - a low-yield device, by its' nature, will be very dirty. It's hard to imagine a terrorist organisation being unhappy with those results.

 

[Horton229]

Naval reactors appear to run around 50%, and they are the highest grade for reactor power. Basic weapons grade is 80%, and higher is better. A crude device will not work on reactor grade fuel. 40-50% only works if it is the secondary stage with a PU core.

The materials in question were, as far as I can ascertain, believed to have been 90% enriched - i.e. weapons grade.

A lecturer of mine speculated that it was something to do with how the fuel rods were made for the liquid metal reactors, but he'd had a few pints.

 

[Horton229]

The point is that even a device that "fizzles" is still going to do a huge amount of damage and cause mass hysteria and panic, even before people figure out it was a small nuclear weapon and not a large conventional bomb. Any terrorist organization would be pleased with that, even if they were also disappointed it wasn't bigger.

A terrorist organisation may well be happy with a fizzle, or even a radiological weapon.

The OP was more interested (as I understood) with a more advanced type of weapon. If you have 580kg of HEU a fizzle a well funded and resourced organisation would have 'wasted' an 'opportunity' if they end up with a 1kt fizzle.

 

[b0ned0me]

It depends on the weapon type, some fizzles can't even destroy the tower they were mounted on.

Fizzles are no rare thing, even in 2006 60 years after the A Bomb was proven to work Nth Korea had a test that fizzled. I'd guess that no NGO could amass the sort of resources that Nth Korea expended to fuck up their bomb.

Really? Every fizzle I have ever heard of was either due to experimental designs, or trying to cut the fissile mass to the absolute minimum, or a combination.

Implosion designs are incredibly complex but very efficient - if they work. Hand someone a massive pile of weapons grade HEU and they will build gun bombs - because while they use a lot of U235 they will work unless the people involved are total numpties.

Little Boy was the first nuclear weapon ever used - a gun type design that used 64kg of HEU of which only 1.3% fissioned, to give 15kt. They never even felt the need to test the desigm since it was essentially guaranteed to work. All the complications start to arise when you want to push the efficiencies upwards to get the most out of a limited amount of fissionables. Fat Man used implosion on 6.2kg of Pu, burning 15% of it to give 20kt.

 

[Horton229]

Really? Every fizzle I have ever heard of was either due to experimental designs, or trying to cut the fissile mass to the absolute minimum, or a combination.

The first test by NK in 2006 is generally accepted to have failed. The yield estimates are from as low as 0.1kT upto 5kT - way below what a normal first test would be. The second test was also under 5kT. The third was ~10kT. Building a tiny yield weapon deliberately is technically more difficult than a standard 15-20kT device so it is extremely unlikely these were anything but failures.

Assuming they had adequate material, it does suggest that as stated earlier, the design is not the hardest part (nor getting the HEU) - it's the whole industrial complex to produce the associated technology. Given that the gun type was used without testing in 1945, it seems unlikely that these failed attempts by North Korea were anything but implosion devices.

The lack of fissile material may have forced the Koreans' hand in terms of going for the more complex, but more efficient, implosion weapon.

 

[Riain]

Really? Every fizzle I have ever heard of was either due to experimental designs, or trying to cut the fissile mass to the absolute minimum, or a combination.

Implosion designs are incredibly complex but very efficient - if they work. Hand someone a massive pile of weapons grade HEU and they will build gun bombs - because while they use a lot of U235 they will work unless the people involved are total numpties.

Little Boy was the first nuclear weapon ever used - a gun type design that used 64kg of HEU of which only 1.3% fissioned, to give 15kt. They never even felt the need to test the desigm since it was essentially guaranteed to work. All the complications start to arise when you want to push the efficiencies upwards to get the most out of a limited amount of fissionables. Fat Man used implosion on 6.2kg of Pu, burning 15% of it to give 20kt.

I'd suggest that any bomb made by some NGO using uranium acquired from Ulba would be experimental and therefore liable to fizzle.

Little Boy was simple as far as nuclear weapon design goes, but it was still a complex piece of kit that requires considerable complex detail design and engineering to work. It required a neutron initiator for example, which is a complication that may not be easily duplicated by some NGO which has gotten the Uranium.

 

[Alternate History Geek]

I'd suggest that any bomb made by some NGO using uranium acquired from Ulba would be experimental and therefore liable to fizzle.

Little Boy was simple as far as nuclear weapon design goes, but it was still a complex piece of kit that requires considerable complex detail design and engineering to work. It required a neutron initiator for example, which is a complication that may not be easily duplicated by some NGO which has gotten the Uranium.

It did not require a neutron initiator - the ABNER initiators were added as an afterthought, just to make absolutely sure. Even without them, Little Boy would have been initiated within a tiny fraction of a second by a neutron or neutrons originating from spontaneous fission or background radiation.

A target designed to stop the projectile once insertion is complete is called a "blind target". The Little Boy bomb had a blind target design. The deformation expansion of the projectile when it impacted on the stop plate of the massive steel target holder guaranteed that it would lodge firmly in place. Other designs might add locking rings or other retention devices. Because of the use of a blind target design, Little Boy would have exploded successfully without the Abner initiators. Oppenheimer only decided to include the initiators in the bomb fairly late in the preparation process. Even without Abner, the probability that Little Boy would have failed to explode within 200 milliseconds was only 0.15%; a delay as long as one second was vanishingly small - 10^-14.

My emphasis.

 

[b0ned0me]

The first test by NK in 2006 is generally accepted to have failed. The yield estimates are from as low as 0.1kT upto 5kT - way below what a normal first test would be.
...
The lack of fissile material may have forced the Koreans' hand in terms of going for the more complex, but more efficient, implosion weapon.

Everything I have read on the DPRK tests says that it was a plutonium imploder - which is very challenging for a first effort by a small country doing it all themselves. Since the quantities of HEU needed for a gun weapon tend to be nation-bankruptingly expensive, everyone seems to go for implosion despite the difficulty.
Nonetheless, fizzles are very rare. A handful or two out of thousands of test shots.

I'd suggest that any bomb made by some NGO using uranium acquired from Ulba would be experimental and therefore liable to fizzle.

Experimental, certainly. But it is like comparing a steam engine to a turbofan. Which would you choose for your first effort at engine construction?

 

[Riain]

It did not require a neutron initiator - the ABNER initiators were added as an afterthought, just to make absolutely sure. Even without them, Little Boy would have been initiated within a tiny fraction of a second by a neutron or neutrons originating from spontaneous fission or background radiation.



My emphasis.

We know that now, but back in 45 there was enough doubt that the neutron imitator was included. Would our hypothetical bomb maker be accomplished enough to make a gun type bomb that will work without the help of the initiator?

I'm a sceptic about the whole thing, from recruiting a bomb designer through to machining the uranium to successfully putting in the right place.

 

[Horton229]

We know that now, but back in 45 there was enough doubt that the neutron imitator was included. Would our hypothetical bomb maker be accomplished enough to make a gun type bomb that will work without the help of the initiator?

I think you answered your own question - back in 45 there was doubt. Today there is just so much information in the public domain that, by definition, was not available back then, that there are no doubts about the gun type needing an initiator. That said the OP is talking 1994 which means there was significantly less information available.

It is no doubt difficult - as mentioned above though, I do not think it is the design that is the problem. It is the construction and the engineering challenges that make this difficult. But without the need to do ANYTHING to get the key fissile material needed, I think it is plausible to build a weapon, and keep it secret. Of course, the more complex you try make it, the harder it becomes to guarantee success without testing.