| 639 | |
|---|---|
 639 thermonuclear test, 3.3 megatons | |
| Information | |
| Country | China |
| Test site | Lop Nur Test Base |
| Period | June 17, 1967 |
| Number of tests | 1 |
| Test type | Atmospheric |
| Device type | Two-stage thermonuclear bomb |
| Max. yield | 3.3megatons of TNT (14 PJ) |
| Test chronology | |
639 was the codename for China's first full-scale test of atwo-stagedthermonuclear device, on 17 June 1967, yielding 3.3megatons of TNT. It followed the first two-stage thermonuclear test, at a smaller 122 kt yield, in December 1966. It was the sixthnuclear test that wascarried out by the People's Republic of China, and represented the completion of the "second bomb" i.e. thermonuclear bomb component of the "Two Bombs, One Satellite" program. With these two tests, China became the fourth nation to develop thermonuclear weapons, following the US, USSR, and UK. Taking place 32 months after the first Chinese nuclear test,Project 596, it remains the fastest progression from nuclear to full thermonuclear test of any country.
The goal of China was to produce a thermonuclear device of at least a megaton in yield that could be dropped by an aircraft or carried by a ballistic missile. Several explosions to test thermonuclear weapon designs, characteristics and yield boosting preceded the thermonuclear test.[1]
China was motivated to pursue nuclear weapons in part due to theFirst andSecond Taiwan Strait Crises in 1955 and 1958. The United States hadthreatened nuclear attacks on thePeople's Liberation Army in each, andstationed nuclear weapons in Taiwan during and after the second crisis. The program officially began on 15 January 1955.
Liu Jie had participated in negotiations of a 1957 "New Defense Technical Accord" cooperation agreement with the Soviet Union, where they had agreed to supply a model nuclear weapon, specifically theirlayer cake design, tested asRDS-6s andRDS-27. Despite using thermonuclear reactions, this was not a true thermonuclear weapon. Liu Jie pressed the Soviet side for details on hydrogen bombs, but realized the Soviets would not supply any details. China had received extensive technical help from the Soviet Union to jump-start their nuclear program.[1] They assisted construction of agaseous diffusion plant forhighly enriched uranium atLanzhou (Plant 504), and alithium deuteride production plant atBaotou (Plant 212). In June 1958 the Soviet Union supplied a 10 MWheavy-waterresearch reactor (HWRR-I) and a 25 MeVcyclotron to the Beijing-basedChina Institute of Atomic Energy. Unlike the US and USSR, at the time of their hydrogen bomb program, China operated no production facilities forplutonium ortritium.[2] In June 1959, therift between the Soviet Union and China had become so great that the Soviet Union ceased all assistance to China.[3] In January 1961, limited thermonuclear weapons research began. The People's Republic of China detonated its first nuclear bomb,Project 596, in October 1964.
Thermonuclear research took place underPeng Huanwu. During 1963, the Soviet layer cake design, which Peng had at some point received limited information on, was extensively investigated as ultimately too inefficient to be reasonably scaled to the megaton range. In January 1964, a search for a new design began. Foreign magazine photographs were searched, showing existing thermonuclear missiles were generally long cylinders, indicating different physical principles from the spherical layer cake. In November 1964,Mao Zedong andZhou Enlai pressured the thermonuclear researchers for a successful test within three years. In mid-1965, plans were made to carry out a small layer cake design test in 1966, and a backup project, "658", a three-staged layer-cake design capable of reaching one megaton, intended for a test on 1 October 1967.[4] This concept was similar to the British backup designOrange Herald Large.
From September 1965,Yu Min,Cai Shaohui, and over 50 other researchers gathered in Shanghai, to focus on rapid theoretical development of the hydrogen bomb. Yu Min held a lecture series on the layer-cake bomb, and in doing so realized its flaw was its slow production oftritium from lithium deuteride i.e. theJetter cycle. Work proceeded for almost 100 days, using both digital computers and manual calculation. During one simulation, a "light nuclear materials" (presumably lithium deuteride and its fusion products[citation needed]) value was mistakenly coded 20 times too large, and astonished the researchers with a three megaton yield. This allowed shifted the focus to methods of strong compression and density increase in the secondary.[4]
In October, Yu and Cai decided to explore less physical but more ideal models for compression of the secondary. Yu subsequently devised a "sophisticated structure" to maximize one form of energy delivered to the secondary (presumablyX-rays[citation needed]). From 1 November, simulations on the J501 computer showed that a one-megaton bomb was feasible with this design. From December, the decision was made to proceed with testing focused on this breakthrough. Yu later stated this rapid development prevented the hydrogen bomb research program from crumbling during the ten-yearCultural Revolution, which began in May 1966.[4]
In China this design has become known as theYu Min configuration [zh] (于敏构型,Yú Mǐn gòu xíng). The Chinese government claims that although it is a multi-stage thermonuclear weapon design, it is distinct from theTeller-Ulam design assumed to be used by the other four thermonuclear nations, allowing further miniaturization, and that together these two comprise the only feasible thermonuclear weapon designs.[5] The differences are unclear, as the Chinese design also channels energy from a nuclear fission primary to compress a thermonuclear secondary. Like the initial Soviet and British hydrogen bombs, the secondary is spherical, unlike the first cylindrical secondaries used in the US.[4]
Despite a theoretically sound multi-stage thermonuclear weapon design, the Chinese government chose to first test the layer-cake design as China's third nuclear test. All testing occurred atLop Nur salt lake. It was codenamed "596L", as it was based onChina's first nuclear device, "596", a fission implosion bomb, but with an extra layer oflithium deuteride represented by the "L". The weapon was tested on 9 May 1966, dropped from aXi'an H-6 bomber, and yielded approximately 220 kt. This yield is consistent with the similar SovietRDS-27 test in their1955 nuclear test series, which yielded 250 kt from a lithium deuteride layer cake design (RDS-6s achieved 400 kt via the addition of tritium).[6]
Next, a small-scale test of the two-stage thermonuclear design was planned, codenamed "629". Development was obstructed by physics issues with the nuclear primary, and the outbreak of theCultural Revolution in May 1966. A tower test was to be used for more precise measurements. To minimizefallout from ground contamination, a 50 meter circle was paved with concrete and a 230 meter radius circle with crushed stones. The device yield was also reduced by the use of less lithium deuteride and a leadtamper, designed for 100 kilotons. The test took place on 28 December 1966, yielding 122 kilotons, and validating the staged thermonuclear design.[6]
Following the successful 629 test, full efforts were devoted to a full-scale hydrogen bomb test as "Test No. 6", codenamed "639". It was decided to cannibalize the materials from backup "658" layer cake project. In the fervor of theCultural Revolution, the Ninth Academy eagerly competed against Peng Huanwu's prediction thatFrance would test its first hydrogen bomb in 1967, and moved the speculative 639 test date from October to July.[6]
The bomb, codenamed "639", was a larger version of the 629 device, a two-stage device with a boostedhighly enriched uraniumprimary, but more lithium deuteride and afast fissioningnatural uraniumtamper greatly enhancing the yield. The device weighed six tons, as opposed to the device of the 629 test, that weighed 1500 kilograms[7].
The device was detonated atLop Nur, inBayingolin,Xinjiang, on 17 June 1967.[6] It was dropped from aXian H-6 (Chinese manufacturedTu-16) of the36th Air Division and was parachute-retarded for an airburst at 2960 meters. The crew was scheduled to drop the weapon at 08:00China Standard Time, but appeared to experience nervousness, failing to release the bomb when over the target. Beijing was immediately informed and Premier Zhou Enlai personally radioed the crew, telling them to remain calm. The bomb was dropped on the second attempt at 08:20.[8]
With successful testing of this large two-stage thermonuclear device, China became the fourth country to have successfully developed a thermonuclear weapon after the United States, Soviet Union and the United Kingdom. Theyield was 3.3megatons.[6]
The film of the prior 1966 tests have been released, as well as an unidentified later test.[9]
It was a fully functional, full-scale, two-stagehydrogen bomb, tested just 32 months after China had made itsfirst fission device. It remains to date the fastest of any country to successfully develop this capability.
Following his death in 2019, Yu Min became the first deceased recipient of theMedal of the Republic, awarded byXi Jinping and theStanding Committee of the National People's Congress.[10]
