China ICBM/SLBM, nuclear arms thread

[ChongqingHotPot92]

Yes indeed.

China now has so much weapon grade U that is enough to make many nukes.

However, the argument here is that U nukes are much bigger and heavier than Pu nukes which are not good for MIRV missiles.

Sorry just a simple question I still have in mind. As much as we all know about the construction of modern thermonuclear warheads, I just want to double check. Is it POSSIBLE to construct a modern high-yield two-stage thermonuclear ICBM warhead WITHOUT any Pu inputs? In other words, just rely on WPU and other Uranium components with absolutely zero Pu component?

 

[ZeEa5KPul]

Sorry just a simple question I still have in mind. As much as we all know about the construction of modern thermonuclear warheads, I just want to double check. Is it POSSIBLE to construct a modern high-yield two-stage thermonuclear ICBM warhead WITHOUT any Pu inputs? In other words, just rely on WPU and other Uranium components with absolutely zero Pu component?

Yes.

 

[ChongqingHotPot92]

Yes.

I am asking this because if China could figure out a way to construct the warheads for DF-31/41s (as well as potential tactical nukes) using only WPU, that could significantly speed up the expansion of the arsenal. It was unfortunate that China shut down the Guangyuan graphite reactor way too early in the 80s, while no efforts were given to complete the massive Fuling site. Had it been completed, Fuling would have become China's equivalent to the Hanford site.

 

[gelgoog]

You can do it. It is just that using plutonium means they will be a lot more compact.

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The critical mass for plutonium-239 is 10 kg vs 52 kg for uranium-235. Plutonium is also more energy dense.

IIRC the plutonium is typically only used in the trigger of a nuke. And you need only a small amount of it.

 

[Kalec]

Let's hear some testimony from actual warhead designer, shall we?

From Hu Side, the third gen chief designer of Chinese nuclear warhead.

His conversation with David Stillman before CAEP cut off communication with the US after 1999 Belgrade embassy bombing.

“With regard to the level of our nuclear weapons development, we don’t need anything from the U.S. We began development of thermonuclear weapons beginning with our third nuclear weapons test and had solved all of the problems by the sixth nuclear
weapons test in 1967. What the U.S. did for us and the whole world was to prove that atomic and thermonuclear weapons worked. That is what you gave us and everyone else.

That was the main secret that you gave away. Everything else we did on our own.” With Hu stopping for a breath of air, I spoke up to compliment him on his contribution to the development of sophisticated thermonuclear primaries, since a few years earlier | had learned that he had been the designer of Chinas first such primary. Hu resumed his peroration: “Yes, but we did not come to the idea of those sophisticated primaries from you [the United States]. This was the only logical way to reduce the diameter of a nuclear weapon in order to fit it into smaller diameter reentry vehicles for the next generation of nuclear warheads as well as third-
generation weapons in particular.

In the late 1970s, China realized that we must reduce the diameters of our next generation nuclear weapons. We understood the general principles involved in sophisticated primaries and the physical laws involving criticality and diameter [as a function of geometry]. We then began to test our nuclear weapons using different shapes based on these principles. The reason we did not successfully design these sophisticated primaries earlier in our program was because we did not have the computer capability needed to design such things. We only began to get this computing capability in the early 1980s. However, even then, that capability came slowly. There was no big jump even though we were getting new, more capable computers. We had to learn how to use the computers as well as how to design these shapes.

“By the late 1980s and up to the mid-1990s, we expanded our knowledge of the nuclear weapon design requirements step by step. We came to agree with your scientists that we had mastered 80 percent and then 90 percent of the full potential [i.e., efficiency] of the nuclear weapon design. The ability to get the last 10 percent would be of very little military value and also very expensive to acquire. We did not see the military requirement for further nuclear weapons tests, nor were we able to justify the expense. So we agreed with you to enter into a CTBT.’ And we thought that, by doing this, we could cooperate with you [the United States] on ending the nuclear arms race. But that apparently was not your [American] idea.”

 

[FairAndUnbiased]

Sorry just a simple question I still have in mind. As much as we all know about the construction of modern thermonuclear warheads, I just want to double check. Is it POSSIBLE to construct a modern high-yield two-stage thermonuclear ICBM warhead WITHOUT any Pu inputs? In other words, just rely on WPU and other Uranium components with absolutely zero Pu component?

It was proven with the 3 stage DF-3 warhead which was IRBM deliverable since the 1970s.

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Historically this was also how China got around NPT concerns and became part of the club.

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由于当时中国钚生产堆建造受阻，美苏密谋签署不扩散核武器条约，企图卡死中国获得合法拥核的权利，为了赶时间，中国利用气体扩散法制造了第一颗原子弹所需要的武器级铀235。这也就导致了中国早期弹头基本都是铀弹头，由于铀的临界质量较大（20KG），导致弹头体积较大，不利于小型化。因此，我国也是所有有核国家中首枚核武器唯一使用铀235装料的国家。

东风5A导弹单弹头是500万吨的大型氢弹（据说是第一颗氢弹加装铀238外壳制成，1976年试爆），由于生产年代早，重量体积较大，性能已较为落后，但由于第一代铀弹芯没有使用氚，导致其寿命极长，应该还有服役。所谓的“只有中国保留有氢弹”的谣言应改为“中国是唯一保留有百万吨大当量导弹弹头的国家”（美国B83是航弹，120万吨）

 

[Deleted member 24525]

Implosion type bombs can absolutely be made with uranium. The idea that implosion requires plutonium and that uranium can only be used for gun-type devices is a bizarre myth that I am guessing started with DC think tankers. The primary and sparkplug in China's first thermonuclear weapons were both uranium. And the enrichment level needed to make an implosion device work with uranium is much lower than for a gun type.

 

[Kalec]

Another interview with Ye Benzhi, one of top chiefs responsible for the explosive part of nuclear warheads

Key takeaway:
1. China didn't master modern miniaturization until the 250kt nuclear test in 1987, at least in the point of view from scientists.
2. The modern one has non-spherical primary, just like W-88 warhead.
3. The primary costs about at least 10 million RMB to build.
4. Ye also believed the main obstacle was the lack of computer in 70s to simulate compression of non-spherical primary.

上世纪70年代，在王淦昌院长的主持下，研究人员提出了许多设想和方案对其中五个方案进行研究对比，被大家称为“五朵金花”，后来逐步集中到其中一个方案上，终于有效解决炸药部件的小型化问题，重量比原先减轻了几十倍。
总的来说，核武器的小型化确实是一项难度极大的难题，正因为难度很大，再加上文化大革命的影响，我国从第一颗氢弹试验成功到基本实现小型化用了约20年时间。
记：核武器小型化主要难在哪里？
叶：第一，由于第二代小型化的核武器，采用的是第一代核武器完全不同的新构型，因此由此产生的技术问题，需要一个个去解决。比如理论设计计算，核武器小型化是一个三维问题，计算方法复杂，在当时计算机存储量和运算速度不足的情况下，设计计算很麻烦，打个比方，就好像把一个皮球在几万分之一秒内压缩成一个乒乓球已经很难，而你要把一个非球形的橄榄球也在几万分之一秒内压缩成一个乒乓球，就更困难了，进行理论设计，必须有精确的参数，能够进行足够精度的数值模扣。我院搞理论设计的同志，把这个复杂的任务分解成14个关键问题和34个技术难点，依靠集体的智慧各个击破。用人脑智能拓展了计算机的功能，完成了程序设计，同时，从实验上来讲，小型化核武器的物理过程很复杂，是对非球形进行压缩，纵向和横向有流动和干扰，测参数也不容易。也不容易。此外，从加工装配上来讲，谁都知道球形比较好加工，而非球形产品是不同曲率过渡的曲面，而且厚度极薄，加工就很困难，我们通过“三结合”，工程技术人员和技术工人们坐在一起集思广益，有一个重要的核部件，仅材料就价值一千多万元，大家献计献策，改造了工艺设备，采用周密的技术措施，保证此部件一次制造成功，创造了十多项国内首创技术。
第二，试验上难度大。在核武器小型化过程中，我们1986年已经停止了大气层试验，全面转人地下核试验，要求核试验近区物理测试技术有重大突破。要在深数百米以至上千米的地下竖井里做核试验，这是很难的，而且要精确测到试验各种数据也并非易事，具体来说，一是空间小，试验用竖井的直径只有1米多，要把核试验装置，测试探头，样品等，全放在里面，布置起来很困难。测试人员戏称：“这是螺蛳壳里作道场”。其二，戈壁滩地面无水，但地下仍有水，这种竖井叫“湿井”，在几百米深处水压大.温度高，探头、电缆、转接头都泡在深水里，要严格密封，而且在高温情况下，要解决对测试系统的影响，美国人为了避免这个问题，专门选择内华达核武器试验场的干井进行试验，而我们只能迎难而上，克服困难，其三，各种信号干扰大，爆炸测试中，中子、γ射线和电磁波集中在一个小区域，对信号的干扰特别大，要分辨不同的粒子束的不同信号，简直是“沙里淘金”。

Ye: In the 1970s, under the leadership of Director Wang Jianchang, researchers put forward many proposals to study and compare five of them, known as the "five golden flowers", and later gradually focused on one of them, finally effectively solving the problem of miniaturization of explosive components, reducing the weight by dozens of times compared with the original.
In general, the miniaturization of nuclear weapons is indeed a very difficult problem, and because of the difficulty and the impact of the Cultural Revolution, it took about 20 years from the successful test of the first hydrogen bomb to the basic miniaturization of Chinese nuclear warhead.

Journalist: What is the main difficulty in the miniaturization of nuclear weapons?

Ye: First of all, because the second generation of miniaturized nuclear weapons, is completely different from the first generation of nuclear weapons, so the resulting technical problems, need to be solved one by one.

For example, the theoretical design calculation, the miniaturization of nuclear weapons is a three-dimensional problem, the calculation method is complex, in the case of computer storage and computing speed is not enough, the design calculation is very troublesome, for example, as if a soccer ball in a few tens of thousands of seconds to compress into a ping-pong ball has been difficult, and you want to put a non-spherical rugby ball also in a few tens of thousands of seconds to compress into a ping-pong ball, it is even more difficult.

To carry out theoretical design, there must be precise parameters that can be numerical mode buckling of sufficient accuracy. Our comrades in the theoretical design decomposed this complex task into 14 key problems and 34 technical difficulties, relying on collective wisdom to crack one by one. At the same time, experimentally speaking, the physical process of miniaturized nuclear weapons is complex, it is a compression of non-spherical shape, there is flow and interference in the longitudinal and lateral directions, and it is not easy to measure the parameters.

In addition, from the processing and assembly point of view, everyone knows that spherical shape is better to process, while non-spherical products are curved surfaces with different curvature transition, and the thickness is extremely thin, so it is very difficult to process. There is an important nuclear component, only the material is worth more than 10 million yuan, we have contributed ideas and suggestions, transformed the process equipment, the use of sophisticated technical measures to ensure the success of the manufacturing of this component in a clean cut, creating more than ten domestic award-winning technology.

Secondly, the test was very difficult. In the process of miniaturization of nuclear weapons, we have stopped atmospheric testing in 1986, and fully transferred to underground nuclear testing, requiring a major breakthrough in the physical testing technology in the near area of nuclear testing. It is very difficult to do nuclear tests in underground shafts hundreds or even thousands of meters deep, and it is not easy to accurately measure all kinds of data for the tests. Furthermore, though the Gobi desert doesn't have water, but there is still water underground, this shaft is then called "wet well", in a few hundred meters with deep water pressure and high temperature. Probes, cables and adapters are all soaked in deep water, to be strictly sealed. The Americans specifically selected the Nevada Nuclear Weapons Test Site dry shaft for testing to avoid this problem. Thirdly, a variety of signal interference, explosion testing, neutrons, γ-rays and electromagnetic waves concentrated in a small area The signal interference is particularly large, to distinguish the different signals of different particle beams, it is "gold in the sand".

 

[ChongqingHotPot92]

It was proven with the 3 stage DF-3 warhead which was IRBM deliverable since the 1970s.

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Historically this was also how China got around NPT concerns and became part of the club.

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"这也就导致了中国早期弹头基本都是铀弹头，由于铀的临界质量较大（20KG），导致弹头体积较大，不利于小型化。"

Well it is saying that early large warheads (I think the ones for DF-5 - called 506, if I am not wrong - weighted roughly 3,000+kg, and the ones for DF-3/4 weighted 2,250kg) are totally fine with just HEU pit (primary). My confusion and question is that would it be possible and sustainable to build miniaturized ICBM warheads (like the 535, 575, W88, W78, or warhead weighing less than 475kg, ideally less than 250kg) with absolutely no plutonium input, while still achieving a yield of at least 300 kilotons? In other words, maintain similar weight-to-yield ratios like those two-stage warheads that use WGPu pits and triggers.

 

[FairAndUnbiased]

"这也就导致了中国早期弹头基本都是铀弹头，由于铀的临界质量较大（20KG），导致弹头体积较大，不利于小型化。"

Well it is saying that early large warheads (I think the ones for DF-5 - called 506, if I am not wrong - weighted roughly 3,000+kg, and the ones for DF-3/4 weighted 2,250kg) are totally fine with just HEU pit (primary). My confusion and question is that would it be possible and sustainable to build miniaturized ICBM warheads (like the 535, 575, W88, W78, or warhead weighing less than 475kg, ideally less than 250kg) with absolutely no plutonium input, while still achieving a yield of at least 300 kilotons? In other words, maintain similar weight-to-yield ratios like those two-stage warheads that use WGPu pits and triggers.

Weight to yield will be lower but 3000 kT/2250 kg is still ~1.35 kT/kg.

So even at 30% lower efficiency (1.0 kT/kg) and assuming a 100 kg base mass for electronics, heat shield, etc then we expect a 250 kT to be 350 kg (100 base mass + 250 yield portion).