allowing for a smaller and lighter amount of high-explosives to be used The tritium in a warhead is continually undergoing radioactive decay, hence becoming unavailable for fusion. Furthermore, its decay product, helium-3, absorbs neutrons if exposed to the ones emitted by nuclear fission. This potentially offsets or reverses the intended effect of the tritium, which was to generate many free neutrons, if too much helium-3 has accumulated from the decay of tritium. Therefore, it is necessary to replenish tritium in boosted bombs periodically. The estimated quantity needed is per warhead. To maintain constant levels of tritium, about per warhead per year must be supplied to the bomb. One mole of deuterium-tritium gas would contain about of tritium and of deuterium. In comparison, the 20 moles of plutonium in a nuclear bomb consists of about of plutonium-239. Tritium in hydrogen bomb secondaries 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-Ulam staging), the sparkplug, a cylinder of 235U/239Pu 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 fission of the sparkplug split lithium-6 into tritium and helium-4, while lithium-7 is split into helium-4, tritium, and one neutron. As these reactions occur, the fusion stage is compressed by photons from the primary and fission of the 238U or 238U/235U jacket surrounding the fusion stage. Therefore, the fusion stage breeds its own tritium as the device detonates. In the extreme heat and pressure of the explosion, some of the tritium is then forced into fusion with deuterium, and that reaction releases even more neutrons. Since this fusion process requires an extremely high temperature for ignition, and it produces fewer and less energetic neutrons (only fission, deuterium-tritium fusion, and splitting are net neutron producers), lithium deuteride is not used in boosted bombs, but rather for multi-stage hydrogen bombs. Controlled nuclear fusion Tritium is an important fuel for controlled nuclear fusion in both magnetic confinement and inertial confinement fusion reactor designs. The National Ignition Facility (NIF) uses deuterium-tritium fuel, and the experimental fusion reactor ITER will also