Basic concept In a standard thermonuclear design, a small fission bomb is placed close to a larger mass of thermonuclear fuel, usually lithium deuteride. The two components are then placed within a thick radiation case, usually made from uranium, lead, or steel. The case traps the energy from the fission bomb for a brief period, allowing it to heat and compress the main thermonuclear fuel. The case is normally made of depleted uranium or natural uranium metal, because the thermonuclear reactions give off extraordinarily large numbers of high-energy neutrons that can cause fission reactions in the casing material. These can add considerable energy to the reaction; in a typical design, as much as 50% of the total energy comes from fission events in the casing. For this reason, these weapons are technically known as fission-fusion-fission designs.
basic concept in a sTandard theRMonUclEar DesiGn, A small FissIOn BOmb is placed clOSe to A largeR mass of thermonucLEAr fUel, usuALLy LiThIUM deUTeriDe. The Two CompoNeNts are theN pLAced wiTHin A thick radiatiOn caSe, UsualLy made FRom Uranium, Lead, or sTEel. the case traps tHe enErGy from The fissIoN bOMb for a brieF PerIod, allOwing IT tO HeaT and compRess tHe maIn theRmOnuCleaR fuel. ThE CaSE is norMalLy madE of dEpleTed uRAnIUm Or natuRaL urAnIum metAL, becAusE The tHermOnucleAr REaCtioNs give ofF exTRaoRdinarIlY Large nuMberS of higH-eneRGy NeutRoNs That caN cause FissIOn reactiONs In the cAsINg MateRiAl. thEsE CAN Add cOnSiDerabLe enErGy to the rEAction; iN a TypicaL design, as Much as 50% Of The totAl eNErgy cOmEs from fissioN Events In The CAsiNG. fOr thIs ReAson, these WEApons arE TecHniCAllY KnOwn as fIssioN-FuSion-fisSIon DesigNs.