Pantex plant continued...
" There are 180 of these cans, and they must pass hurculean tests : a 30-foot drop to a slab, a 40-inch drop to a spike, a 1475 degree F. Fire for 30 minutes, immersion in water for eight hours, and a load of 6,500 pounds for 24 hours.
Inside the secondary is a " wrapper " of heavy uranium-238. The wrapper covers a sealed cylinder of lithium deuteride and a central plutonium rod. The lithium deuteride is pyrophoric -- it ignites spontaneously if exposed to air -- so it requires special care. The plutonium rod is removed, cased and stored. Any other valuable materials are recovered, and the rest is ground to bits.
The B-61's " primary " -- it's fissionable core -- is dismantled at Pantex in one of the plant's 12 " gravel gerties, " semiburied structures in which a thick gravel-and-sand cap covers a " cell " with reinforced walls. In the event of an accidental chemical explosion that might disperse plutonium, " the gravel would rise a few feet and settle down, containg the radiation, " explains Jerry Hemphill.
Working on the gravel-covered cells, gloved technicians wearing lead aprons and shielded face masks remove the primary's outer casing. Inside they may find an " electric blanket " -- a heater designed to maintain the chemical explosives at an optimal temperature. Beneath the blanket is the spherical shell of explosives, protected by a close-fitting jacket.
Thirty-two or more exploding wire detonators are bonded to the outside of the spherical primary ; their job is to symmetrically ignite the chemical explosives. Each detonator is connected --- through high speed, solid-state switches -- to it's own capacitor. Like a car engine, an atomic bomb has a capaciter discharge ignition.
Located near the detonators are thermal batteries, devices that have a long shelf life and can deliver a lot of current on demand. During the arming sequence, the batteries charge the capacitors, which discharge across the detonators when the firing signal is given. While the bomb is being disassembled, the detonators and their capacitors are shorted, so that external electromagnetic fields cannot somehow induce a discharge.
The chemical explosives on the exterior of the spherical primary are high density (almost twice that of water), high-energy stuff, far more energetic and fast-burning than dynamite, yet very resistant to unintended discharge from shock or heat. Workers use a water-jet saw to cut through the dark, waxy material, revealing the bomb's core. The hemispherical shells of high explosives that are removed are later burned on trays in an open field.
With the explosives removed, technicians can see a protective plating of gold or another enert material. Beneath it is steel-grey beryllium, or uranium-238 -- the spherical tamper. As the chemical explosive wave rushes inward, the tamper's mass acts as a hammer that strikes the plutonium pit -- the bomb's fuel -- from all directions simultaneously. The pit is suspended in the center of the hollow tamper's inner cavity.
This insignificant-looking, grapefruit-size lump contains energy that can level cities. Heavier than a lead ball of the sae size, the sphere is perpetually warmfrom it's steady release of energy. Plutonium is highly reactive, so the pit is hermetically sealed in a jacket of stainless steel or a similar metal. " If you can picture a grapefruit skin with the fruit removed, " says Tom Walton, " the steel is like the yellow part of the skin, and the plutonium is the white part just under the yellow. The inside is hollow. "
The steel jacket prevents the pit from giving off particles that could be inhaled or ingested, but it does not block the carcinogenic gamma radiation emitted by the plutonium. The amount of radiation that workers receive depends on how close to the plutonium they are, how long they are exposed, and how well they are shielded. Pantex permits workers to receive up to one rem of radiation a year, one fifth the government's limit for radiation workers.
The average person who does not work around radiation receives a little more than a third of a rem per year from natural radiation, medical X-rays, and other sources.
Overcrowded igloos
The plutonium pits removed from weapons are placed in holders that fit inside steel containers. The containers are stored in 18 of the 60 igloos on the Pantex property ( the others are reserved for weapons). " We have always [stored] pits here, but only temporarily, " says Hemphill. Until recently, the pits were sent to Rocky Flats plant outside Denver to be made into new bomb cores, but that plant is now inactive. Pantex currently has the capacity to dismantle approximately 2000 warheads per year, but at any rate, the plant will run out of storage space for the plutonium pits around the end of this summer.
Continued in next post...
