W76 (nuclear weapon)

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The W76 is a thermonuclear warhead of the United States and Britain . The W76-0 and its modernized form W76-1 currently represent the main component and therefore the largest part of the US strategic nuclear arsenal . Alongside the W88, it is the second warhead to be used on the Trident II D-5 .

history

The W76 warhead and Mk-4 re-entry missile (sectional view) - Image from Los Alamos National Laboratory

With the beginning of the development of the Trident SLBM for the Ohio class SSBN , which is also under development , the USA needed a new light warhead for this weapon system. Development of the W76 began in May 1973. During development there were some problems with the W76, for example the warhead detonated with low explosive power during a test on the Nevada Test Site and the detonation system was found to be vulnerable to the effects of nuclear attacks . The first warheads were completed in June 1978 and mass production began the following November. The development cost 128 million US dollars. The Mk.4 re-entry heads have been produced by Lockheed Missiles & Space since 1977. The final production of the W76 / Mk.4 took place in the PANTEX facility of the Department of Energy in Texas . In 1978, the first warheads were put into service on Trident I C-4 missiles. In July 1987, production was stopped, by then 3,400 warheads had been produced. The production of the Mk.4 re-entry heads ended at Lockheed-Martin after 23 years in mid-2000 with about 5,000 units produced.

The W76 has long been criticized for being unreliable, especially after the moratorium on nuclear weapons tests in 1992. This is mainly due to the "radiation case", which contains the nuclear fusion fuel. According to statements from developers at Los Alamos National Laboratory, the wall of this uranium cylinder is only as thick in some places as that of a beer can, even if it is supported by a special plastic. The task of this cylinder is to reflect X-rays for a few fractions of a second after the “primary” (the nuclear fission part of the weapon) has been ignited, which provides the energy to ignite the fusion fuel. However, there are doubts that the cylinder will retain its shape during this period, even the smallest deviations could lead to turbulence, which would prevent the initiation of the nuclear fusion and thus the W76 would detonate only with low explosive force.

Therefore, work has been going on to modernize the warhead since the early 1990s. From the year 2000, the plans for the modernization were concretized, with the aim of delivering the first modernized warhead W76-1 / Mk4A in the 2007 fiscal year. The modernization includes a new neutron generator, a new system for arming and detonating the warhead (Arming and Fusing Subsystem, AFS) and better protection against shock loads. For the first time, attention was paid to drastic cost optimization in a nuclear weapons project in the USA. The new ignition system developed by Sandia National Laboratories is intended to provide the warhead with new ignition options in addition to increased safety and reliability. The improved warhead is now also capable of contact detonation with increased accuracy, so that it can now also be used against "hard targets" such as missile silos. Since 2008, the entire SLBM fleet has been converted to the Trident II D-5, so that once the modernization to the W76-1 / Mk4A standard has been completed, all missiles will have the ability to attack hard targets, as originally required for the system. Of the approximately 3000 W76-0 / Mk4 warheads that were still in the active and inactive stock of the USA in 2007, around 2000 are to be upgraded to the new W76-1 / Mk4A standard. The program will run until 2021 and 6 billion USD cost. At the end of 2008, there were 718 W76-0 / Mk4 and 50 W76-1 / Mk4A in the active nuclear weapons inventory of the USA (plus 40/10 as replacement). The remaining warheads belong to the inactive inventory. Each Trident II D-5 currently carries 4 to 6 warheads, but can carry up to 14.

Originally there were plans to replace the W76-1 with a new warhead as part of the Reliable Replacement Warhead (RRW) program. This program was rejected by the US Congress in 2007 and 2008 . The administration under US President Barack Obama has declared that the US will not build any new nuclear weapons. Therefore, work on the Life Extension Programs (LEP, deployment time extension measures) for the warheads will be expanded in the future. In 2009 the US Congress allocated US $ 13 million to develop a new ignition system for various US nuclear weapons. It is currently planned to equip the W76-1 / Mk4A with the new system in 2039.

The warhead is the only type of nuclear weapon currently kept operational by the UK. The British warheads are also being modernized to the W76-1 / Mk.4A standard. Like the American warheads, the British are stationed on Trident II D-5 missiles, on Vanguard- class submarines .

design

The W76-0 is a two-stage warhead based on the Teller-Ulam design. It contains a deuterium - tritium boosted implosion explosive device as the first stage ("primary") with plutonium as the fission material with a beryllium neutron reflector. The polymer-bound explosive PBX-9501 is used to ignite the core . The nuclear fusion stage ("Secondary") contains lithium deuteride (with 6 Li) in a coat of enriched uranium . This stage is surrounded by a thin-walled cylinder made of uranium and a layer of plastic, the so-called "radiation case", which is supposed to reflect X-rays after the ignition of the first stage . This supplies the energy to ignite the nuclear fusion. The warhead is capable of both contact and height detonation.

As part of the modernization to the W76-1 / Mk.4A standard, the warheads receive a new ignition system called the MC4700. This system allows the warhead to determine flight path deviations and to adjust its explosion height accordingly, in contrast to the old system with a fixed explosion height. This significantly increases the range of uses of the warhead against hard targets such as missile silos.

Data

Explosive device W76-0 W76-1
Re-entry head (RV) Mk4 Mk4A
status active stock active stock
operator US Navy US Navy
developer LANL LANL
Start of development May 1973 2000
Start of production April 1978 Mid 2007
End of production July 1987 in front. 2020
number of items produced 3400 planned around 2000 (from W76-0 stock)
in the available US stock 2017 385 1215
design Teller-Ulam , two-stage Teller-Ulam , two-stage
Mass with zip 91.7 kg n / a
Length with zip n / a n / a
maximum diameter with zip n / a n / a
Explosive power 100 kt 100 kt
Carrier system Trident I C-4, Trident II D-5 Trident II D-5
Number per carrier 1 to 8 (possible 12) 1 to 8 (possible 12)
Scattering circle radius about 100 m to 375 m about 100 m

See also

Individual evidence

  1. ↑ a b c d W76 at nuclearweaponarchive.org
  2. ↑ a b c W76 at globalsecurity.org
  3. ↑ a b - US Nuclear Forces 2009
  4. ^ British Submarines to Receive Upgraded US Nuclear Warhead
  5. ↑ Declassified Stockpile Stewardship Plan ( Memento September 10, 2008 in the Internet Archive ) of the United States Department of Energy
  6. ↑ Hans M. Kristensen, Matthew McKinzie, Theodore A. Postol : How US nuclear force modernization is undermining strategic stability: The burst-height compensating super-fuze , Bulletin of the Atomic Scientists, March 1, 2017
  7. ↑ Hans M. Kristensen & Robert S. Norris (2017) United States nuclear forces, 2017, Bulletin of the Atomic Scientists, 73: 1, 48-57
  8. ↑ Russianforces.org: How many warheads?