| I. Materials > The Uranium-Plutonium Chain > Fabrication of Nuclear Weapons |
The design and fabrication of nuclear weapons demands research and development (R&D) in various domains: neutronics, detonics, electronics, radiochemistry, metallurgy . . . The major part of the R&D on nuclear weapons takes place in the centers of the Direction des applications militaires ( Dam) of the CEA: Vaujours-Moronvillliers (Seine-Saint-Denis), Bruyères-le-Châtel (Essonne), Valduc (Côte-d’Or), Le Ripault (Indre-et-Loire), and Cesta (Centre d’études d’Aquitaine, Gironde). (The Vaujours center, but not its Moronvilliers annex, was closed at the end of 1997; the Limeil-Valenton center closed at the end of 1999.)
From the beginning of the military nuclear program, it was necessary to master complex problems. To trigger the explosion of a fission bomb, one can use two methods. The simplest, the gun device, consists of violently bringing together by means of a classic explosive two sub-critical masses of fissile material to create a supercritical mass. The other is the method called implosion. Conventional explosives are arranged around fissile material in spherical form. At the moment of ignition, the explosives compress the fissile material and an external neutron generator directs a stream of neutrons onto the plutonium core, setting off a fission chain reaction [Coyle 88; DAM v.88].
The "canon" method necessitates enriched uranium as the fissile material. The implosion method can use enriched uranium 235 or plutonium or a combination of the two. Because France, in 1960, did not have military enriched uranium, it was necessary to use the implosion method to explode the first nuclear device, named Gerboise bleu.
After the pure fission bomb, the CEA developed the fission bomb boosted with thermonuclear materials and then the thermonuclear head with two stages. For the makers of bombs, the development of a thermonuclear bomb represents an advantage, because a thermonuclear bomb with two stages needs less fissile material per kt than a simple or a boosted-fission bomb.
The nuclear tests that set off chain reactions took place in Algeria and in Polynesia. These tests are outside the scope of this book (for more details see Barrillot 96). But there are also tests called "cold firings" that are carried out in France-at the Polygone de Moronvilliers (Marne), at Cesta and at Valduc--as well as formerly in Polynesia.
The Dam characterizes the cold tests by saying that they are "to verify the behavior of different components of the nuclear device, with the exception of the fissile material, either simultaneously, or separately" . . . The fissile material of a nuclear device is "simulated by an inert metal" [DAM ii.79]. "Inert" means that the material cannot trigger a chain reaction, but it can be radioactive. Depleted uranium and plutonium are among the materials used.
At Valduc, nuclear subassemblies are fabricated in series, and at Le Ripault classic explosives are assembled. However, the CEA subcontracts the fabrication of weapons components to various companies. Its subsidiary Cogéma produces nuclear materials, for example, and another subsidiary, Sodern, develops and produces neutron generators in its plant at Limeil-Brévannes (Val-de-Marne). The assembly of entire warheads takes place today at Ile Longue (Finistère), but it has been carried out in the past at Le Ripault, at Cesta, on the plateau d’Albion (Vaucluse), and at a military site within the perimeter of the the CEA-Valduc center.
Paradoxically a category of "conventional" weapons is fabricated with a "nuclear material." Depleted uranium is used for tank armor and for projectiles.
The main property of depleted uranium that attracts weapons designers is its extreme density, three times that of steel. Moreover, projectiles of depleted uranium mixed with a little titanium offer minimal resistance to air. They have an excellent power of penetrating armor and, on penetration, catch fire, releasing smoke composed of an aerosol of oxide particles, in general less than five microns. From 10% to 60% of the uranium in a projectile is scattered in that form [Damo iv-vi.94; LeMo iv.95].
In France, Cerca at Bonneuil and at Romans played an important role in the development of these weapons. At the beginning of the 90s, Cogéma and particularly the Annecy factory of Sicn (100% subsidiary of Cogéma) took over the work in the area of depleted uranium. Other establishments that have fabricated or assisted in the fabrication of depleted uranium weapons include two establishments belonging to the Délégation Générale pour l’Armement: l’Etablissement technique de Bourges (Cher) and the Centre d’études de Gramat (Lot), an establishment of Giat Industries at Salbris (Loiret-et-Cher) [Damo 4th quarter 98].
-updated July 3, 2001
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