Power plants Nuclear marine propulsion

a nuclear fuel element cargo ship ns savannah. element contains 4 bundles of 41 fuel rods. uranium oxide enriched 4.2 , 4.6 percent u-235

as core of seagoing reactor smaller power reactor, probability of neutron intersecting fissionable nucleus before escapes shielding lower. such, fuel typically more highly enriched (i.e., contains higher concentration of u vs. u) used in land-based nuclear power plant, increases probability of fission level sustained reaction can occur. marine reactors run on relatively low-enriched uranium requires more frequent refueling. others run on highly enriched uranium, varying 20% u, on 96% u found in u.s. submarines, in resulting smaller core quieter in operation (a big advantage submarine). using more-highly enriched fuel increases reactor s power density , extends usable life of nuclear fuel load, more expensive , greater risk nuclear proliferation less-highly enriched fuel.

a marine nuclear propulsion plant must designed highly reliable , self-sufficient, requiring minimal maintenance , repairs, might have undertaken many thousands of miles home port. 1 of technical difficulties in designing fuel elements seagoing nuclear reactor creation of fuel elements withstand large amount of radiation damage. fuel elements may crack on time , gas bubbles may form. fuel used in marine reactors metal-zirconium alloy rather ceramic uo2 (uranium oxide) used in land-based reactors. marine reactors designed long core life, enabled relatively high enrichment of uranium , incorporating burnable poison in fuel elements, depleted fuel elements age , become less reactive. gradual dissipation of nuclear poison increases reactivity of core compensate lessening reactivity of aging fuel elements, thereby lengthening usable life of fuel. life of compact reactor pressure vessel extended providing internal neutron shield, reduces damage steel constant bombardment neutrons.