Cladding graphite

Structural materials - Fuel particle coatings - pyrocarbon, silicon carbide. - Spherical fuel element matrix and cladding - graphite. - Reactor module - Hastelloy-N alloy... 

The core clad/graphite temperature is estimated to be 949 K for the 500-kWh(t) core thermal power. Ten years of operation at 500 kW yields an energy output of 1.826 MWd. The heavy metal mass of the fueled regions is 4.59 MT, yielding a core average bumup at end-of-life of 398 MWd/MT. 

To slow down and control the rate of reaction, a moderator is also required. Typically, the moderator is boric acid, graphite, or heavy water (D20) and is present in the high-purity water, which also serves as a primary coolant for the fuel and the reactor vessel. The tremendous heat generated by nuclear fission is transferred to this closed-loop coolant, which is contained within a reactor primary-coolant circulation system. The high-purity water coolant also contains a suitable pH buffer such as lithium hydroxide, which has the additional effect of limiting the corrosion of fuel-cladding and other components. 

The high-temperature gas-cooled reactor (HTGR) is a thermal reactor that produces desired steam conditions. Helium is used as the coolam. Graphite, with its superior high temperature properties, is used as the moderator and structural material. The fuel is a mixture of enriched uranium and thorium in the form of carbide particles clad with ceramic coatings. 

Graphite is used as cladding for nuclear fuel elements because of its low neutron-absorption cross section and good moderating properties, as well as its high temperature properties and high heat capacity. 

The graphite cladding is fabricated by extrusion. The extruded and baked tubes are impregnated with pitch and furfuryl alcohol in a pressure autoclave and baked to achieve a low gas permeability (10 cm/s). 

The rate of reaction of B4C graphite bodies with metal cladding is appreciable only above 800=C ... 

Cladding Mg alloy Stainless Graphite Zircaloy Zircaloy... 

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