Tritium consists of about 4.5 kilograms of plutonium-239. Since tritium undergoes radioactive decay, and is also difficult to confine physically, the much larger secondary charge of heavy hydrogen isotopes needed in a true hydrogen bomb uses solid lithium deuteride as its source of deuterium and tritium, producing the tritium "in situ" during secondary ignition. During the detonation of the primary fission bomb stage in a thermonuclear weapon (Teller-Ullam staging), the sparkplug, a cylinder of U-235/Pu-239 at the center of the fusion stage(s), begins to fission in a chain reaction, from excess neutrons channeled from the primary. The neutrons released from the
Tritium 65 nuclear sites in the US. In one case, leaking water contained of tritium per litre, which is 375 times the EPA limit for drinking water. The US Nuclear Regulatory Commission states that in normal operation in 2003, 56 pressurized water reactors released of tritium (maximum: 2,080 Ci; minimum: 0.1 Ci; average: 725 Ci) and 24 boiling water reactors released (maximum: 174 Ci; minimum: 0 Ci; average: 27.7 Ci), in liquid effluents. According to the U.S. Environmental Protection Agency, self-illuminating exit signs improperly disposed in municipal landfills have been recently found out to contaminate waterways. The legal limits for tritium