back to article Duff UK nukes risk 'popcorn' multi-blast accident apocalypse

Last week many Britons were amazed to read in the quality press that the UK's nuclear weapons are thought to have a "design fault" which could see a transport accident detonating multiple warheads in a devastating chain reaction apparently known as "popcorning". "More than 1,700 warheads are affected by the problem which would …


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  1. Pete Silver badge

    no way to know

    Given that it's over 40 years since any major power has tested a nuclear SYSTEM (i.e. put a bomb on a missile, fired it, got to the target and have it detonate) it's not unreasonable to say that none of the nuclear weapons we have today have ever been fully tested. Letting one off in an underground facility doesn't simulate the rigours of launch/space-travel, so there's no way to know if the device would work - or detonate, or fail due to adverse conditions whilst in flight.

    Even worse is that with the passing of time, all the engineers and designers who gained experience from the "live" tests are now either dead or retired. The people working on nukes today learned their trade second-hand from the people who actually blew things up. If they're new to the industry, their knowledge and experience is probably third-hand.

    While you can run some intensive computer programs to simulate the explosion and even the aging process inside a device, you're limited to simulating things you know about and can test in the real world. Will a nuclear device detonate if someone hit it in many places simultaneously? We'll never know, but I personally don't ever want to give one a kick, to find out.

  2. David Adams

    So it's a long shot then.....

    ..... But as anyone who reads Terry Pratchett will know, a Million to 1 chance will come off 99 times out of a hundred!

    We're doomed!

    The lead lined one with the tinfoil hat please.

  3. Adam Foxton

    "Nuclear technology equals little children dying in agony."

    Whereas with coal mines they just got blacklung and died by 15. If they weren't caught in a pit collapse.

    Coal mines and fossil fuel combustion technologies in general have killed more people in the last 100 years than Nuclear power has. Hell, the sun, wind and rain- all those lovely friendly smiling renewables loved so much by anti-nuke campaigners- have killed more in the last 100 years than Nuclear power. This is mainly evidenced by the fact that we can name the different nuclear accidents (chernobyl [incidentally, human error caused this rather than design flaws], 3-mile-island [human error + design flaws], Nagasaki, Hiroshima) but cant' remember where was flooded- it's a frequent occurance so no-one cares.

    What people don't realise is that anything suitably energetic to power our civilization is incredibly dangerous.

    Also, nuclear technology rocks and is still futuristic- even after 50 years. Its derived weapons have been used in war twice rather than at 600 rounds per minute somewhere around the world pretty much 24/7.

    Oh, and to get back on-topic, Popcorn nuclear detonations are unlikely, so don't worry about them.

  4. Anonymous Coward
    Anonymous Coward

    Shock! Horror! Probe!

    Nuclear weapons are dangerous?! Well blow me down and vapourise me.

    What will journalists find out next?

  5. Anonymous Coward

    Design fault? Yes.

    "It isn't that the current ones are thought likely to go off in such a scenario; it's just that you can't prove they won't, as this wasn't part of the design spec.

    Not really a design fault as such, then."

    No, hang on. If it *was* designed to withstand multiple impacts and it *didn't*, that would not be a design flaw, it would be a total f*** up.

    If it wasn't designed to withstand multiple strikes, that's a design flaw. It SHOULD have been designed that way. That's like saying vulnerabilities in Windows aren't design flaws because Windows wasn't designed to be secure. It should have been; ergo design flaw.

    Monsieur Sarkozy, can we borrow a pacific atoll to test one of our warheads please?

  6. Calvin Davidson

    Sorry, but...

    ... I think you'll find that smoking fags is the most evil thing you can ever do.

  7. Anonymous Coward
    Anonymous Coward

    I already stopped.

    Is it me, or have pretty much all papers resorted to blog style overtly inflamatory stories of late?

  8. Anonymous Coward

    yes Lewis

    But as I will be staying this summer in a flat that lost all it's windows to a accidental munitions explosion I would have to say why risk it with a nuke?

    It's not like I will ever benefit from these devices after all it doesn't actually bother me which bunch of ass hats I pay my taxes to.

    Would you really notice if you lived in a dictatorship?

    The only person I know who's tried it can't see much difference.

  9. Barry
    Paris Hilton

    And I thought that video games were the greater danger...

    ... and it turns out that nuclear weapons are actually more dangerous. Who'd have thought it?

    Paris: because a nuclear blast is 'hot'.

  10. Ken Hagan Gold badge

    Re: summer news drought have spent the last year making statements that would have had "August" written all over them in my youth. (I think the best recent one was "let's meet our energy requirements in an environmentally sound fashion by chopping down every tree in the land".)

  11. steve dixon

    Duff headline, more like it!

    "Duff UK nukes risk 'popcorn' multi-blast accident apocalypse"

    Is this one of the worst headlines ever in journalism?! Quite possibly. Sort it out, please.

  12. Ceilidhman


    More worrying is the propellant used, it's not that forgiving of being bashed around. A missile was dropped from a crane at Faslane sub base on the Clyde a few years back. If it had gone off, it would have likely spread the fissile core across much of Glasgow and surrounding towns due to prevailing winds. Not good.

    Incidentally, Faslane's emergency protocols for such an event extend as far as the perimiter fence, which is very reassuring for the rest of West Scotland.

    Mine's the one with lead lining

  13. Anonymous Coward

    Other great article, but...

    So "popcorn warhead design fault will lead to innocent kids dying in agony" can probably be filed in the same place you'd file "terror threat means all civil liberties must be suspended"

    It that the likelihood then mines the CRB suit with the lead lined codpiece

  14. Anonymous Coward
    Anonymous Coward

    JSP 538

    At a shelf worrying 552 pages long JSP 538 may well be dull but makes a fantastic door stop and pest control weapon.

    For further JSP related fun try "JSP 536 - Ethical Conduct and Scrutiny in MoD Research Involving Human Participants"; "JSP 320 - Permitted uses of Farm Animals" and "JSP 813 - Instructions for Service Bands and Military Musicians: The policy for all MoD bands and for the provision of musical support to the Services." A wealth of highly tenuous scary stories can be generate by a wilfull misreading of any of these, secure in the knowledge that no one (apart from Mr. Page) will try to wade through them to discover the mundane truth.

  15. Dodgy Geezer Silver badge

    A Prize for the best idea...*

    "Popcorning requires many implausible events to happen in sequence...."

    So if you think hard and create a near-impossible scenario, you can imagine people dying half a mile away from an accident with a nuclear bomb? Fine.

    I suggest that Reg readers start thinking about possible but implausible scenarios with tree-hugging institutions like bird reserves where the same numbers might die. For instance, boatloads of glacier-watchers could output so much diesel smoke that the snow around them melts and swamps their boat... (Oh, I forgot - that's already happening..)

    *prize offer invalid for persons living on planet Earth...

  16. Anonymous Coward

    Hmmm popcorn

    Now who's going to supply the salt/sugar for all that popcorn then?

    And who the f*#k has a screen big enough to need a nuclear 'accident' to create enough popcorn for the viewing.

    That being said, it might be enough to watch the lord of the rings trilogy in full. whilst only dying of boredom rather than hunger (is popcorn good enough substinance?)!

    But then I read the story and found it had nothing to do with cinema style food, more like hollywood style plots.

  17. Anonymous Coward
    Anonymous Coward

    Implausible = flying an airliner into a New York building

    Well, we were told it was implausible. Till it happened. Twice.

  18. Anonymous Coward
    Anonymous Coward

    @steve dixon

    You must be new here. </slashdot>

    Personally, I think it was a great headline. I remember thinking that the New Scientist article seemed a little bit FUDdy.

  19. Vladimir Plouzhnikov

    Fatal radiation exposure?

    For people within 1 km of the epicentre of a nuclear munitions dump going critical?

    I think these people will have other things to worry about - such as being pulverised by overpressure, burned to cinders, shredded by flying glass and buried under tons of rabble. A gamma ray overdose will not really matter much by that stage.

  20. Les Matthew

    quality press

    In the UK?

    That was a joke, wasn't it?

  21. Anonymous Coward
    Anonymous Coward


    If you really can provide a powerful enough kick to compress a plutonium core enough to trigger a nuclear explosion then I certainly wouldnt want to meet you!

    Note the article at no point mentions a nuclear blast - this is describing a situation that triggers part of the conventional trigger and subsequently dispersing bits of core and tritium over the surrounding area. Of course, a lot of the warhead is made of u-238 and is not radioactive.

    Note that even in the 'worst case' they dont suggest a fizzle or low yeild explosion.

  22. Jerry

    They're tougher than you think

    The world has a long and glorious history of 'broken arrow' incidents.

    The Americans have blown up, dropped, burnt and just plain lost a variety of nukes. To this day there is one sitting in the shallows off the East Coast of the US (oops, now just where exactly did I drop that nuke??)

    The design of them is inherently safe from accidental full detonation. You need to arm them with a mighty complex process that isn't fully completed until it's been dropped from the aircraft or even moments before intended detonation. Even if the initiating explosives go off in a fire you won't get a lot of nuclear energy released - mostly bits of plutonium spattered around the site.

    What is of more interest is what happens when you fly a nuke in just after another one has gone off properly. There is a huge amount of radiation and spare neutrons floating around that can prematurely trigger (fizzle) the following warhead if it's the wrong design. For this reason alone, the designs are made so that quite severe nearby nuclear events are highly unlikely to ignite a fully armed and ready to go warhead. This makes unarmed warheads pretty safe indeed.

  23. LuDo
    Black Helicopters

    No wonder

    all kind of jabber around the nuclear threat helps pushing the right-wing go-get-those-mullahs agenda

  24. Alex

    @Implausible = flying an airliner into a New York building

    Meh, it doesn't rly count when it's a conspiracy by the gov :P

  25. Steven Cox

    Am I the only one....

    that thinks that it it wont make much difference whether 1 nuke goes off or 3+ for this popcorning to happen (if it can) i am guessing that the nukes would have to be pretty close to each other so the over all result wont be that much different...

  26. Sean Aaron

    Bottom line, we don't need them

    These weapons have no use in the British military arsenal; given that we cannot even complete manufacture without components from the States they aren't even properly British!

    It's a complete waste of money renewing them; our submarine "fleet" would be more effective as a deterrent with weapons we would actually deploy like conventional warheads. If South Africa can give up their nukes in an arguably much more unstable part of the world then we certainly can!

  27. anarchic-teapot

    Bloody dangerous stuff, popcorn

    Broke a tooth on some at the cinema last week. Damn right it should be banned.

  28. Alan

    To paraphrase "Broken Arrow"

    I don't know what's scarier, popcorning nuclear accidents, or that it happens so often there's actually a term for it

  29. Anonymous Coward
    Paris Hilton

    1,700 warheads?

    Where does the Telegraph pick that figure from?

    We have fewer than 200 - the usual number quoted is about 170. Even at the height of the Cold War we never had more than 350.

    Bad typo, methinks.

    (Paris, because even she can tell the difference between 1,700 and 170, especially when it's the price of a frock.)

  30. Dave Bell

    Extreme Po[pco]rn

    Can't we just amend the new law on Extreme Porn and ban this horrifying threat to out precious bodily fluids?

    (New Scientist seems to be setting a new record here, even worse than when Farmers' Weekly reported on Chernobyl.)

  31. Chris
    IT Angle

    Small point...

    Do ANY of you have any idea just how tricky it is to make a fission (never mind fusion) bomb actually go BANG? As opposed to just 'fssstttt'?

    Trust me on this. It ain't easy. Indeed, if it were, there's quite enough unaccounted for bomb grade fissile material kicking about out there that we'd have heard just how easy it is - literally.

  32. TeeCee Gold badge

    Does it matter?

    Surely in the astonishingly unlikely event of a popcorning event with a selection of warheads, the most likely outcome is that one or more of them will go BANG properly.

    Thus neatly rendering any issues with the others irrelevant and determining whether popcorning was the cause impossible.

    Arses covered? Check. Next risk please.

    Right. Who vapourised my coat?

  33. Dunstan Vavasour

    Straw Man

    Spreading FUD from such implausible extrapolation is just a variant of the Straw Man approach. More usually they conclude with a "think of the children", so nice to see a variation.

  34. goggyturk

    No popcorn?

    Ceilidhman: "A missile was dropped from a crane at Faslane sub base on the Clyde a few years back. If it had gone off, it would have likely spread the fissile core across much of Glasgow and surrounding towns due to prevailing winds", doesn't the fact that it didn't pop off demonstrate that they are safe? Sounds like a single impact event to me..

  35. TMS9900
    Thumb Down

    So... wasn't news then? Just propaganda?

    ElReg: Can we have a hammer and sickle icon please? For propaganda dressed up as 'news'.


  36. Anonymous Coward
    Anonymous Coward

    @Calvin Davidson

    >... I think you'll find that smoking fags is the most evil thing you can ever do.

    Well, it is pretty cruel, but I didn't think we were allowed to call them fags anymore?

    >Implausible = flying an airliner into a New York building

    >Well, we were told it was implausible. Till it happened. Twice.

    When were we told that? Tall buildings have been an aircraft risk since aircraft first started flying. It's why they have flashing lights all over them.

    On the whole though, the nukes are useless and expensive, we should ditch them.

  37. Kane

    Re: So it's a long shot then.....

    I think you'll find it's 9 times out of 10 (but it might just work....)

    Mines the black leather one with "PEDANTIC" sewn on the back in shiny studs....

    (another Pratchett reference)

  38. Louis Cowan

    Next Rockstar title

    Grant theft nuclear paedo terrorist. Can't wait!

  39. 4a$$Monkey

    Nuclear technology equals little children dying in agony

    And it could cause the mutation of the general public into a zombie army of pedo-terrorists!

    Think of the children people!

    Coat > Mines the one with the chainsaw and boomstick

  40. James Anderson


    The danger the article seems to be concerned with is that the triggering machanism is accidently set off.

    No amount of bumping and banging will ever upset tritrium, uranium 235 etc.

    The hydrogen isotopes need to be saturated with gamma rays to set of the fusion reaction. The only practical way to acheive this is a conventional nuclear explosion (either classic WW II uranium 235 or the more rock n' roll fifities plutionium isotopes).

    So the mechanical triggering mechansim is the one to set of the conventional nuclear explosion. This involves putting lots of the stuff together to acheive critical mass very very quickly -- do this too slowly and you just get lots of heat and radation but no bang.

    There are lots of ways to acheive this but they all involve using chemical explosives (usually WW I vintage cordite) to move the lumps of isotope together withing the required timescales.

    So the only thing that could be set off by bumping and banging is the conventional explosive trigger. This mechanism can quite easily be tested to destruction by replacing the lumps of isotope with lumps of lead and putting it through various stress test (hitting it with punic war vintage rocks for example).

    Historicly nuclear weapons have an excellent saftey record and only killed the people they were pointed at.

    Now dont get me wrong I have always objected to nuclear weapons. But purly a matter of principle -- its wrong to kill civilians and infately more worng to do it en mass.

  41. michael

    @Adam Foxton

    "name the different nuclear accidents (chernobyl [incidentally, human error caused this rather than design flaws], 3-mile-island [human error + design flaws], Nagasaki, Hiroshima)"

    sorry to be a pedent but Nagasaki and Hiroshima where delibrate not acdients

    and you missed winscale/selifeild where the graphate at the core or the recator caught fire in one of tehre tests

  42. Matthew LaShure

    From experience...

    From my experience, it is always the thing that seems least likely, and the most remote of possibilities, that always happens.

  43. Cameron Colley

    RE: Implausible = flying an airliner into a New York building

    How was that implausible? Granted, not something most people would think about when talking terrorism -- but once the idea has been proposed it doesn't seem implausible (yes, I know there's hindsight involved here, but hijacking and suicide bombing in vehicles have been used for decades).

    I used to read Pravda ^H^H^H^H^H^H New Scientist back when it was about science, such a shame it's turned into Political Hype weekly.

  44. Anonymous Coward

    New Scientist...

    ...that'll be the type with a media degree then. aka: scientist mediocre.

    Dear HR department, a scientologist is NOT a geologist/phycisist/chemist/otherist that specialises in science!

    Seriously though where have all or scientists actually gone? and can I come too? theres just loonies left here....

  45. David Pollard

    Counterfactual testing?

    It's hard to know what to make of this story, even though sublining in D.Tel is usually clear enough to decipher.

    Is it a mish-mash pot-boiler alluding to the Elitzur-Vaidman bomb-tester (, a cover story for the re-working of Trident warheads into bunker-busters (arguably in contravention of arms limitation treaties to which the UK is committed), or part of a softening-up exercise for nuclear waste storage proposals which neglect the more effective denaturing that fourth generation reactors could afford?

  46. blackworx

    *Sigh* It's not nuclear...'s neucular. Neu-cu-lar.

    Excellent stuff. Always looking forward to your next article Mr. Page. Without exception they are engaging, educational and hysterio-bullshit-free. Hats off to you sir.

  47. Eddie Edwards

    What am I missing here?

    The warheads used in Hiroshima and Nagasaki were measured in kilotons. They devastated whole cities. The warheads we have today are measured in megatons. There is no missile shielding in the world that will not melt if standing 10 feet away from a megaton warhead going off. Of course they'll "popcorn" in that scenario. Who cares? One warhead going off at location A, ten going off at location A ... everyone's going to die anyway.

  48. Parax

    @What am I missing here?

    The difference between going Critical and going SuperCritical!

    but hey science hand carts and hell.. who cares.

  49. Anonymous Coward

    @Eddie Edwards

    Nuclear Reactors dont detonate like a bomb they blow apart like Chernobyl. This is the difference between going critical (chernobyl) and going supercritical (a-bomb) basically you have to contain the mass more and hold it together well beyond its critical mass, if its not held together it burts apart.

    Bombs do this very fast with very carefully balanced explosives, in a massivly controlled manner any other mechanism of joining the material together (eg nearby explosion) wont be in perfect balance and will cause criticallity and nuclear predetonation (aka fizzle) causing it to burst apart but not detonate this causes lots of radiation as stated 1km = 16xDeadly but not a very big blast.

  50. Dodgy Geezer Silver badge

    What are you missing here?

    You're missing your brain and associated thought processes, if any.

    A nuclear weapon is NOT an explosive. It's a machine, built to create the conditions which prevail in the Sun (for a short time!). If you hit or burn most machines, they do not start to operate, they break. So would a nuclear bomb.

    Explosives are used to move parts of this machine, in a similar way to large springs. These might explode if you hit the machine hard, but that's not a nuclear explosion. That would be the same as some springs in a clock jumping out if you hit it with a hammer or put it on a bonfire. But, like the clock, that doesn't mean the machine is operating, it means it's disintegrating....

  51. Anonymous Coward
    Anonymous Coward

    @Eddie Edwards

    What you are missing is that no one is talking about nuclear explosions here.

    A common misconception is that modern devices use more U-235 or Plutonium than the WWII devices. The WWII devices where extremely inefficient. The U235 bomb was only 2% efficient and the PU bomb about 15% (both were used in 1945). Modern devices are much more efficient.

    The upshot of this is that the amount of radioactive material in modern devices is in the kilos. Plutonium is actually pretty safe, you can even handle it safely for short periods of time as it only really throws out alpha particles.

    If a device 'popcorned' you would disperse plutonium over a small area (say an acreor less), which would be relatively easy to clean up, with no real lasting fallout. Tritium could be released, which may be in gas form and would disperse pretty quickly.

    Now even if the impossible happened and the primary nuclear trigger fizzled , you would be talking about a sub 10 kiloton explosion at ground level. The area affected would be most likely similar to the damage caused by the fuel depot explosion in Buncefield. Most of the power and radioactive fallout in a thermonuclear bomb comes from the 'secondary' device which is a further fission reaction with a fusion trigger. The secondary is usually made up of more plutonium with an optional amount of uranium 238 (Which is not radioactive).

  52. Nigel


    What you're missing is that the guy is claiming it could happen by accident, starting with an accident such as a warhead being dropped or caught in a fire.

    Which it couldn't. I'm not privy to any secrets, but the basic physics is well-known.These things are made out of a hollow sphere of Plutonium that is imploded, by means of many almost-simultaneously detonated explosive charges, to form a super-dense super-critical Plutonium mass at the centre.

    If the assemblage is distorted, or if the explosive charges are not detonated in exactly the right time sequence to within microseconds (maybe nanoseconds) the result will be just a conventional explosion and some Plutonium scattered around the neighbourhood. Very bad for anyone close at the time, very expensive to clean up afterwards, but definitely not Hiroshima.

    So in purely relative terms and thinking only about accidents, they're "safe".

  53. Dave

    To avoid the problem...

    ...we just need to make sure no one is allowed to take liquid in containers of greater than 100ml capacity anywhere near the weapons.

    Mine's the one that does not have Omnius Prime on the front.

  54. Scott

    Pardon me, I'm off to cower in my bunker.

    I might poke my head out in a few years. I'll see you guys then (if anyone's still alive).

  55. allan wallace

    @ anonymous coward's reply to Eddie Edwards.

    Quote "Plutonium is actually pretty safe, you can even handle it safely for short periods of time as it only really throws out alpha particles"

    Don't forget plutonium is actually VERY POISONOUS even if it's not, radioactively speaking, that dangerous.

    and if you dropped it on your toe and didn't have safety boots on, it could really hurt....

  56. PT

    RE: Implausible = flying an airliner into a New York building

    Indeed, who could ever have thought of such a thing. Even Tom Clancy, when he published the plot 10 years earlier, could only imagine the aircraft flying into the Capitol in Washington DC.

  57. Anonymous Coward
    Anonymous Coward

    "worst case"?!

    "In the worst-case scenario, people a kilometre away would receive a radiation dose of 100 sieverts - that's 16 times the lethal dose."

    Unless I've been ripped off and my hard-earned tax poonds have been frittered away on something that will fizzle rather than blow, people a kilometre away would only be exposed for that radiation for a very very short period of time before being vapourised by the rapidly expanding fireball. A typical mid-range hydrogen bomb (which is presumably what UK-owned warheads are) produces a fireball with a radius of many kilometres, and the blast wave and incident heat radiation is going to be leaving silhouettes of people frozen in attitudes of surprise, terror, or strangely shaped baggy-arsed trousers a lot further out than that. The WORST case is presumably multiple simulataneous detonations producing something like the Tsar Bomba, whose mushroom cloud punched right through into the stratosphere, and nearly blew the aircraft that dropped it out of the sky at a range of 100km. Oh and the glow was seen in Finland.

  58. Bloody_Yank
    Jobs Horns

    What were you blokes thinkin' ?

    I'm sure our 'merican made nukes are much safer ... our problem is we just can't keep track of them. The Air Force loads them on bombers and flies them around the country like they were friggin' UPS packages.

    I predict in the next 25yrs there will be a "nuclear event" somewhere in the world. Sort of like playing Russian Roulette with a map of the world and a shaky trigger finger.

    If not - I'll be dead and miss the whole show ! Oh Crap

    Balmer - cuz that crazy shit would press the button if it would boost sales

  59. Nigel

    You can handle Plutonium

    Quote "Plutonium is actually pretty safe, you can even handle it safely for short periods of time as it only really throws out alpha particles"

    Yes, you can. Richard Feynman did, while he was working at Los Alamos on the bomb. In his memoirs, he comments on how it felt warm (from the heat the radioactivity was giving off). He lived until 1988. On the other hand he died of a rare cancer.

    I have always suspected that the story about Plutonium being an extreme chemical toxin is a myth. However, radioactively it is EXTREMELY dangerous once it's inside you. Alpha particles are stopped by your skin (the already-dead outer layer thereof), but a tiny particle of an alpha emitter inside you massively irradiates the surrounding tissue, until it goes cancerous. Also Plutonium in solution gets locked into bone, cue leukaemia or bone cancer.

    Which is why a non-nuclear detonation of a nuclear bomb trigger would be very bad news for the people downwind of it.

  60. call me scruffy


    For the record the UK operates "variable yield" warheads that can be set between 300t (Note! Tons, not Kilotons!) and 100Kt... These are not the multi-megaton metropolis busters of the 60s!

    Also, unless we've broken a treaty, we also have drastically less than the 1700 warheads quoted in the article! At the moment a mere 48 warheads are available on patrol at any one time.

    (And personally since nobody's tried to nuke us yet I'd say that our nukes are doing _exactly_ what they were built for!)

    Heart, because I've learned to love the bomb.

  61. Peter Fairbrother

    UK atomic weapons

    Britain has "about 200" nuclear weapons, all of which are Trident warheads. Usually about 144 are in submarines, the rest are stored and maintained at Coulport near Glasgow. There are at present no foreign nukes on UK mainland soil.

    UK Trident warheads are based on the US W-76 warhead, and have yields of either 10 kilotons or 100 kilotons. There are no UK megaton-range weapons.

    The UK Trident warhead primary is (probably) a small and light beryllium-reflected DT-boosted neutron-pulse-tube-initiated plutonium fission bomb with a 300 ton or so unboosted yield, using a minimum amount of plutonium in the pit. This plutonium pit is reshaped and compressed very quickly by conventional explosives to create a supercritical mass. The required shaping and compression must be very accurately controlled.

    In the old days the compression was controlled by using a large number of very high-speed detonators, which had to be set off with sub-microsecond timing. We don't know how modern bombs work, but speculating, UK bombs may only have one detonator. The use of a single detonator would mean that the bomb would be "single-point sensitive".

    "Single-point sensitive" means that a single jolt of energy correctly delivered could cause a significant nuclear energy release. "Single point safe" means that it takes more than one jolt of energy. There are other possible causes of single point sensitivity, however all of these would result in smaller energy releases.

    To increase the primary yield a mixture of deuterium and tritium is injected into the primary pit just before the primary is compressed, which boosts the primary yield to 10 kilotons. This cannot happen in a single-point failure or popcorning accident, the injection of the DT mix must be deliberate and accurately timed.

    While 10 kilotons is enough to ignite the fusion secondary to give the full yield of 100 kilotons (if the secondary is fitted, some warheads don't have a secondary), 300 tons isn't, so a full-yield event cannot be caused by popcorning or single-point failure.

    In the case of a Trident warhead the very most that a single-point or popcorn accident could produce is a 300 ton yield unboosted primary detonation, although even this is an overestimate. as to get the 300-ton yield a neutron-pulse tube is required, which needs pre-charging and precise timing control - like DT injection, the neutron pulse not going to happen in that sort of accident, which means that the yield will be lower than 300 tons.

    "Popcorning" might at worst involve a single unboosted primary of 300 tons yield going off. - nearby bombs would then release a significant amount of plutonium, but they are extremely unlikely to add significant amounts of energy, In general the neutron and X-ray flux of the first explosion would disrupt the plutonium pits long before they could be accurately compressed by their conventional explosives. The chance of getting two or more 300-ton yields is so remote that it isn't worth bothering about.

    This is not to say that UK warheads may not be somewhat "duff" - there is a large question about the reliability of the US W76's secondary, and it may often fail in use, only giving a 10-15 kiloton yield. We don't know whether the UK's version has the same problem though.

  62. Peter Fairbrother

    Re: Yield

    I don't know this for sure, but I don't think UK warheads are dial-a-yield as such.

    They can of course easily be modified to give 300 tons (by emptying the DT reservoir), 10-15 kilotons (by fitting a dummy secondary) or be full 80-100 kiloton yield devices, but I think this has to be done in the maintenance shops, and once aboard the subs the yield can't be changed.

    Also, I don't think the 300 ton option has actually ever been fielded, just the 10 kt and 100 kt options.

    I think most subs on patrol carry at least one missile with a single 10 kt warhead.

    But as I say, I'm not sure about this.

  63. Neoc

    Re: @Eddie Edwards

    "Nuclear Reactors dont detonate like a bomb they blow apart like Chernobyl."

    I hate to be a pedant, but the Chernobyl *reactor* did not blow - the ancillary equipment (like the boilers) blew up, fracturing the reactor casing. Said reactor was already well on its way to a meltdown (the name says it all) and the crack simply "helped" it along.

    Nuclear *reactors* can't blow up on their own, they're not designed for it. The worse you'll get is a melting core which oozes radioactive material all over the complex (and from there to just about anywhere else).

  64. Michael Fletcher

    Lewis Page's writing

    I'm a bit concerned about subliminal, or even liminal, messages hidden in Mr Page's stories.

    As soon as I read that last line about drinking booze, I had an almost irresistable urge to crack open a beer.

    Surely the potential for millions of Reg readers to do Mr Page's bidding is far more frightening than any half-arsed nuclear catastrophe.

  65. Dr Patrick J R Harkin

    So a nuke going off will kill people...

    I dunno. First they bitch about MOD equipment NOT being capable of doing its job, and the next minute....

  66. Peter Fairbrother

    UK atomic weapons part 2 - popcorning

    In part 1 I described how in order to reshape and compress the plutonium pit in order to get a 300-ton yield the conventional explosives must be very accurately detonated, but what happens if the explosive is not detonated accurately?

    The details are complex and the knowledge needed to give accurate answers is well beyond what's publicly available, but for high yields the supercritical mass must be formed very quickly so that it doesn't blow itself apart before it has time for a lot of the mass to undergo fission - in the 300 ton case "a lot" is about1% of the plutonium.

    If a critical mass of formed more slowly, perhaps because the explosives were not detonated correctly, then a small yield "fizzle" can happen. This isn't very likely, as there isn't a lot of extra plutonium in a modern primary, and it has to be shaped into a sphere and also be compressed before a critical mass can be assembled, but it is perhaps possible. This is the other main cause of single point sensitivity, but what would the yield of such a low-order detonation be?

    Well it can't be more than 300 tons, because getting 300 tons is the maximum that can be done with accurate detonation, but it may be ten kilos, a ton or even ten tons depending on the speed of assembly and the degree of supercriticality. More than ten tons or so yield is very unlikely, bordering on impossible.

    Could this set off another low-order detonation in a nearby warhead? It's possible, although unlikely. How unlikely? Only the MOD could answer that, it depends on classified details of the design.

    Lets look at a worst-case popcorning scenario, where the 48 warheads in a sub or in a store do set each other off in low order detonations. Note that a single medium-order 300-ton detonation will be enough to disrupt the remaining warheads.

    If each warhead yielded the maximum10 tons then the total would be 480 tons, but for two too-long-to-explain-here reasons 350 tons is a better maximum figure, and even this is extremely unlikely - even 50 tons is pushing probability.

    However lets say the maximum credible total yield for a single point failure or popcorn event is 350 tons - now this isn't spare change by any means.

    The effects of sub-kiloton explosions are a bit different to multi-kiloton explosions, and it is quite possible to be killed by prompt radiation without suffering lethal blast or burn damage (though you will still get knocked ass-over-tit). That's what the 100 sieverts at 1 km figure is about. Think "neutron bomb", although neutron bombs are designed to give off lots of neutrons, and typically have yields in the low kiloton range.

    However, any remotely likely popcorning event can only take place where there are several warheads close together, ie either in a sub or in a bunker, and the prompt radiation will be attenuated by the hull of the sub and perhaps the water, or the walls of the bunker. The raw radiation will consist of neutrons and gamma rays of approximately equal lethality.

    The gamma rays will be attenuated by the hull of the sub by a factor of at least 500, and would not be a great concern at 1 km. The neutrons are much more of a worry, but a few feet of water or bunker walls would stop them from being lethal at 1 km.

    In general, at 1 km distance from a popcorning event I'd be far more worried about contamination from plutonium than prompt radiation.

    Is a popcorning event possible at all? For some early warheads undoubtedly the answer is yes, but could today's UK warheads popcorn? I don't think so, but that depends on classified design details I have no access to. The official line is "It's perhaps possible but extremely unlikely, we can't prove it but it may well be impossible". I'd agree in general, though perhaps not on exactly how unlikely.

  67. Anonymous Coward
    Thumb Up

    I can't believe (at time of submission) this hasn't been posted already...

    ...but I just can't wait for the ID cards to come, they'll save us all.

    Interesting comments, picking up some interesting snippets from further research etc

    @ Neoc: "Nuclear *reactors* can't blow up on their own, they're not designed for it."

    I fully understand there's some fairly rock solid safeguards preventing a nuclear reactor blowing up of its own accord, however I'm not sure "they're not designed for it" really suffices as a reason, I'm sure there's plenty of appropriate analogies to reinforce what I'm trying to say but it's gone 5 o'clock and I'm hungover as it is.

    I've never really looked into the whole nuclear good/bad thing very deeply but thinking about it, they're rather obsolete currently, they were designed for a time when "Prior to satellite intelligence, each side lacked precise knowledge of the location of the other side's military and industrial facilities" and I suppose one big bang to do as much damage as possible is a pretty good idea if that's what you're after. But I believe MIRVs are now the preferred weapon of choice, combined with all the satellite information available they seem to make pretty good sense.

  68. Snert Lee


    If UK atomic weapon storage sites are not protected against time traveling interdimensional gateways being used to abscond with said weapons, then the public needs to be warned about that too.

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