James ActonJapan a "long weekend" from the Bomb

Regular Wonk readers will know that the question of how long it would take Japan to build the Bomb has been a subject of interest in the past. See here and here for starters.

Well, we now have a new low-ball estimate. Global Security Newswire (not exactly a scoop for ACW, I know) reports a speech from Gary Sick last week:

Experts have told him that Japan is so close to a weapons capacity that Tokyo “could do it, sort of, over a long weekend.”

I’d just love that word: “experts”…


  1. CKR (History)

    I worked in a program in which the leaders knew they could have their results “over Fourth of July weekend.” Then it was Labor Day weekend. Then…well, to make a long story short, they never really got to where they wanted to.

  2. hass (History)

    The Japanese should just come clean about their nuclear weapons program . . .

  3. Yale Simkin (History)

    It is absolutely correct that Japan could (if it really truly decided to commit) have an easily deliverable by existing missile, functioning, compact, multikiloton uranium-gun assembly warhead using off-the-shelf HEU and with components machinable in less than a week.

    I found that earlier ACW thread on Japan’s capability so egregiously nonsensical that I didn’t even bother pointing out is deficiencies at the time.

    One can be as snarky as one wants, but physics and engineering are REAL.

  4. Dean (History)

    By that logic, I, am capable of a bomb over a long weekend, since the fundementals of physics are available to us all. Yet, how does the fact Japan is the only country to have a nuc dropped on them figure into the calculus? If it is so easy, why haven’t they?

  5. Haninah (History)

    There’s an old Israeli joke (from back in the day when Israelis worked a six-day workweek) that Israelis will build a city in five days just so they can take a long weekend. Just thought that seemed appropriate somehow for this context… 😛

    (I should also add, “from back in the day when Israelis actually built things themselves.)

  6. Tim H (History)

    I know of no gun-type designs in any country deliverable by any missile system Japan possesses. How’s that for a deficiency?

  7. Mark Gubrud

    As usual, Yale is right on the tech. I am embarrassed that in that earlier thread I was too timid to go beyond defending “as little as a few months” in the face of assertions that it would take Japan years to develop a nuclear weapon.

    I think there is a difference of assumptions here, though. I was assuming there would be some minimal lead time to establish authority, procedures, responsibility, where the assembled weapon would be housed, etc., and that they might spend some time considering what was the best option, even after a decision to get a deterrent ASAP. I think those who were saying several years were assuming a normal political and bureaucratic process and an effort to field a reasonably sophisticated, robust, durable, and certainly implosion-based weapon. Yale speaks of a gun-type bomb which Japan has the resources to put together in less than a week, and which could be deliverable by a missile (although this would also require some kind of reentry vehicle). I agree they could do this, but I think it’s unlikely that they would do things that way in any plausible scenario.

  8. Llewelyn Hughes (History)

    To: Yale Simkin · Dec 11, 09:55 AM

    Mark Gubrud is right. The assumptions are indeed different. Physics and engineering are certainly real, but so are the human systems that are in fact needed to implement and manage the program. Someone would have to decide to build a bomb, persuade his/her colleagues and the public it was a good idea, requisition the materials from a number of private sector electricity companies that would suffer commercially and therefore be likely to oppose, institute the myriad human systems to ensure its proper management. Without thinking about the problems of human systems the statement “Japan could build a bomb over a weekend” amounts to hyperbole, IMHO.

  9. Yale Simkin (History)


    Notice what I stated:

    if it really truly decided to commit“ which covers the “human” factors you describe.

    The tone of the original offhand comment, Experts have told him that Japan is so close to a weapons capacity that Tokyo “could do it, sort of, over a long weekend.” , was meant to be provocative, as was my delineating the technical possibilities.

    Unless Godzilla was rising from beneath the waves, the Japanese would certainly take a more deliberate path than cobbling together a quick and dirty (and quite unsafe) device.

    I don’t understand tho, what the private sector electricity companies have to do with it. The large stockpiles of HEU are in government hands. The actual number of people required is remarkably small.

    Tim wrote – “I know of no gun-type designs in any country deliverable by any missile system Japan possesses. How’s that for a deficiency?”

    Very true. Thats why they would build one. The US had thousands of uranium guns, each less then a meter long, 1/5 meter wide and 110kg, in its active arsenal until the early ’90s, when they were pulled with the other tactical devices.

    Since we are in an historical mode, consider this:
    Until the early ’90s, Japan fielded the Nike Hercules.

    The N-H was usable in an air attack and surface attack mode and was designed to mount, in addition to its usual HE warhead, the W31 nuclear warhead, which was 1 meter by .75m and 500 kilograms.


    If the Japanese did decide to go with a CRASH program to roll-out a Pu-based, intercontinental range, RV-ed, repeatable and safe warhead and matching launcher arsenal, then 6 months for the first usable models to be tested should likely be possible. They already have many of the pieces (the point that the “experts” in the first post were likely alluding to.) If I have time (or if any one is even interested) I can show the different parts that Japan has.

    The 2 years that the Japanese have previously reported to roll out nuclear arms have a couple of built-in show-slowers.

    One is that it is deliberately paced program, not a wartime crash program, building institutions, and creating a finalized production design and system. This is not the way a dynamic wartime program would do it.

    And secondly, it proposes not using existing fissile stocks, but building an entire fuel cycle of production reactors, reprocessing plants, weapons fabrication factories, missile test and production systems, etc.

    Yeah, under those specifications even 2 years may be not long enough.

  10. kme

    How much of an impediment to weapons production is contamination of Pu-239 with Pu-240? Am I correct in assuming that LWR are considered less of a proliferation risk solely because the spent fuel they produce contains significant quantities of the heavier isotope?

  11. Rwendland (History)

    Re delivery systems. The Japanese did/do have the M-V all-solid 3 or 4 stage satellite launch vehicle, capable I believe of putting 1800kg into LEO. Last two launches in 2006. I’m not aware of any other country using all solid-fuel rockets for satellite launch, so this has always seemed strange.

    Japan is now working on a next generation solid propellant rocket: “we will reduce the time needed for the operation of ground facilities and launches to about one fourth of the time required for the M-V Launch Vehicle … where the launch control system is not necessarily at the launch site anymore.” Hmm, that’s really useful for the occasional satellite launch!

  12. MTC (History)

    Mr. Simkin –

    1) Mr. Hughes is correct, the engineering and physics are not the issue, even in a situation where Japan has 2 tons of HEU upon its territory. Assembly of a nuclear weapon cannot be considered divorced from the creation of a nuclear weapons program.

    2) Why would an H-2A solid-fueled rocket be insuffient as a launch vehicle for your putative gun-type weapon?

    3) There is no such thing as a “dynamic wartime” anything in Japan. The usual suspects who go to all the conferences in the U.S., wave the Hinomaru and promise boots on the ground “eventually” like to scare people with the spectre of Japan going nuclear “Unless…” These incorrigeable reprobates paint a misleading picture of the intellectual world of modern Japan—only fringe elements contemplate threatening a nuclear breakout as a means of extorting security guarantees from the United States.

    One cannot do something unless one wants to do it—parts on a bench do not just magically assemble themselves into a warhead—and no imaginable Japanese government wants nuclear weapons…and no imaginable U.S. government would want Japan to have them.

    So if you are not talking about a realistic political scenario, what are you talking about? The only possible answers are a rogue program or one hidden from the public and the IAEA. But then we are not talking about time required to go nuclear, as a rogue or clandestine program would not have an identifiable start date. It could indeed could already be in place.

    In a possibly related question, why is the word “human” in quotation marks in your comment of December 12?

  13. Steven Dolley (History)

    “Am I correct in assuming that LWR are considered less of a proliferation risk solely because the spent fuel they produce contains significant quantities of the heavier isotope?”

    No, not according to US DOE, or the NAS. But that’s what many Japanese Pu fuel cycle advocates would have you believe.

  14. Yale Simkin (History)

    KME wrote: “How much of an impediment to weapons production is contamination of Pu-239 with Pu-240?

    The short answer, in regards to Japan is:

    It Does Not Matter

    If Japan preferred to augment HEU warheads with ones using plutonium (or create composite cores), they could turn to the Joyo Fast Reactor. It contains 40 kg of supergrade (+98% Pu239) plutonium in its breeding blanket – sufficient to make at least 10 warheads.

    However, as to your question…

    Reactor-grade Plutonium (RGPu) has (1) a higher radioactive emission, (2) generates much more thermal energy (heat), and (3) has a much higher background of neutrons (which trigger the chain reaction).

    Issue 1 makes manufacturing and handling a bit more hazardous. More protection is required, with shorter worker exposure times, and the electronic and sensitive components must be placed properly.

    The heat problem must be considered in design. Either the core (if contained within the explosive shell) must have active or passive cooling – via heat pipes or similar,

    or preferably, the core is stored outside the implosion assembly. It is easily kept cool actively or passively that way. The core is automagically inserted just prior to explosion.

    This is called In-Flight Insertion (IFI), and it was the norm for the original US nuclear arsenal. (It is vastly safer that way)

    The US was working on utilizing IFI for its modern fleet of “sealed pits”, but that was stopped when nuclear testing ending in the ’90s. Good idea, tho.

    The final issue is high neutron background. The chain-reaction should not occur until the core is properly compressed. If it occurs too early the explosive power is lessened (a fizzle).

    The worst fizzle that Fat Man would have had if it used RGPu, was about 2/3 kiloton. The most likely yield was more than a kiloton.

    Second generation nukes – levitated pits, high speed implosion – essentialy 1950 US level, would have minimal effect on it nominal yield.

    Modern boosted nukes (mid-1950s technology) are predetonation resistant and can use, in principal, RGPu seamlessly. They only yield about 1/3 kt, which ignites the fusion booster which in turn fissions the rest of the core.

    Pointing out that RGPu can be used in any size atomic warhead, from a sub-kiloton demolition mines to a city-destroying hydrogen bomb, the weapons designer Ted Taylor says:

    “Utility of Reactor Grade Plutonium in Nuclear Weapons
    June 10, 1998
    Contrary to opinions expressed by many nuclear engineers that are not familiar with the still secret intimate details of nuclear weapon design and operation, plutonium extracted from all types of spent fuel removed from nuclear power plants or research reactors can be used for making modern fission or thermonuclear weapons that are reliabily predictable in performance, over a very wide range of yields, from fractions of a kiloton to megatons of high explosive equivalent. This has been true for decades, and confirmed by numerous nuclear weapon tests.
    It is true that the first generation of implosion type fission bombs, such as the one that destroyed Nagasaki in 1945, could “fizzle” and produce much lower than the design yields if the plutonium they contained were of “reactor grade.” This could be the result of premature initiation of a fission chain reaction by spontaneous fission neutrons emitted by Pu-240 or other isotopes that are more abundant in reactor grade than weapon grade plutonium. But ways to avoid this problem, by use of plutonium in different designs that could be reliably used for fission and thermonuclear weapons were developed and demonstrated before the end of the 1950s. The performance of these weapons is not significantly degraded by using reactor grade plutonium instead of weapon grade plutonium.”

  15. Yale Simkin (History)

    Rwendland wrote:
    I’m not aware of any other country using all solid-fuel rockets for satellite launch…

    Interestingly, all solid-fuel launchers are rather common.

    A sampling…

    Israel: SHAVIT

    India: SLV , ASLV , PSLV

    Russia: ROKOT , PRIBOY

    China: KT-1


    JAPAN: J-1 , LAMBDA 4 , M-V , Mu-3

  16. FOARP (History)

    Why is the question of whether Japan could build a bomb over a weekend being asked? Japan is protected by the US nuclear umbrella, no country would dare conduct a nuclear strike on Japan without first being sure that the Americans wouldn’t intervene. Far more pertinent is the question of whether Taiwan and South Korea could put together bombs within a two-week time span (i.e., the amount of time they could reasonably be expected to hold out under attack from their respective enemies).

  17. Yale Simkin (History)

    The NTI had an article on the pace and strategic/political value of Iran’s weapon development

    As an aside, the varying potential of other countries was discussed. As part of the list, Japan’s capability to arm almost overnight was noted. Since this was a topic on ACW in the past, James Acton made (IMNVHO unwarranted) mocking note of that claim.

  18. Tom (History)

    Let’s not forget that Japan has perhaps several hundred kilos of US-supplied weapons grade plutonium in the form of critical test assemblies. It appears that this currently unused material is low on the take-back list of the Global Threat Reduction program. Why no active efforts to take back this material?

  19. sweetfancymoses (History)

    “…and no imaginable U.S. government would want Japan to have them.”

    Will you please elaborate?

  20. Rwendland (History)

    Yale – excellent list of solid-fuel satellite launchers.

    I was writing sloppily I’m afraid. What I meant to write was that I wasn’t aware of any other designed-from-scratch solid-fuel rockets entirely for civilian satellite launch; i.e. excluding ICBM/MRBM developments, or effecively prototypes for ICBM/MRBMs.

    I think all the others you list are military related, which highlights the oddity of Japan’s solid-fuel series of civilian launch vehicles, which are still under active development.

    There is a 2003 news report that an ISAS director is “fearful by national security arguments raised by lawmakers for keeping Japan’s solid-fuel rocket technology alive after the two space agencies merge in October [2003].” Looks like a continuation solid-fuel programme has been agreed since then.

  21. Yale Simkin (History)

    Rwendland nicely points out the intertwined relationship between military and civilian solid launchers. Often, the civilian laucher is a reworked military machine.

    It can go the other way, too.

    I am starting to investigate the “hidden” proliferation that is occuring by reworking innocent strap-on solid rocket boosters as missiles. I can see the possibility that IRBMs and ICBMs may become a trade item disguised as simple harmless solid boosters.