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PBX (explosive)

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First developed in 1947 at Los Alamos Scientific Laboratory, plastic bonded explosives (PBX) were intended to make the high-explosive components of nuclear weapons have "adequate energy content, mechanical properties, sensitivity, and chemical stability required for stockpile[d] nuclear weapons. The first was PBX-9205, a mixture of RDX explosive and polystyrene binder. In the U.S. nuclear program, responsibility for PBX development later moved to Lawrence Livermore National Laboratory.[1]

Key to a PBX is the polymer coating, in the range of 5-20% of the total weight, that bonds the explosive granules into a solid, stable mass. Plastic bonding decreases sensitivity to accidental explosion, but does not eliminate it, or pass the one-point safe criterion in weapons, unless the explosive(s) are designated as insensitive high explosives. Two main explosives were used in the late 1990s, RDX and TATB; only TATB is insensitive.

Choice of polymer, and of the bonding technique, involves both careful design, and continued verification through the production and storage phases. "Too brittle a PBX can sustain damage in normal handling and succumb to extreme temperature swings or thermal shocks, while too soft a PBX may be susceptible to creep and may lack dimensional stability or strength."[1]

PBXs have other applications than the implosion systems of fission devices, although those are the most critical. They are used in slapper detonators that initiate the main implosion system.[2] PBXs have been used for explosive welding[3] and precision cutting. They can be used as rocket propellants, and the feasibility of their disposal through cryocracking is superior to that of other large solid rocket propellants. [4]

References

  1. 1.0 1.1 Anders Lundberg (December 1996), High Explosives in Stockpile Surveillance, Lawrence Livermore National Laboratory
  2. , 4.1.6.2.2.6 Detonation Systems, 4.1 Elements of Fission Weapon Design, Nuclear Weapons Archive
  3. David R. Gardner, Courtenay T. Vaughan (October 1997), The Explosive Welding Simulation, The Development and Performance of a Message-Passing Version of the PAGOSA Shock-Wave Physics Code, Sandia Report SAND97-2551 UC-705, pp. 23-24
  4. L. Whinnery et al. (May 1995), Particle Size Reduction of Propellants by Cryocycling, Sandia Laboratories, Sandia Report SAND958227 UC-721