Refractory coated particle fuel

Refractory coated particle fuel, which retains fission products at temperatures much higher than normal operation and postulated accident conditions... 

Even if the RCCS is assumed to fail, passive heat conduction from the core, thermal radiation from the vessel, and conduction into the silo walls and surrounding earth (Figure 5.18) is sufficient to maintain peak core temperatures to below the design limit. As a result, radionuclides are retained within the refractory-coated fuel particles without the need for active systems or operator action. These safety characteristics and design... 

A more advanced development in nuclear fuel technology is the coated-particle concept, originally designed for the high-temperature gas-cooled reactor. The use of small particles of fuel and fertile material, individually coated with impermeable surface layers, and dispersed in a refractory medium such as graphite, has permitted the operation of reactor cores at high temperatures with minimum release of activity into the coolant gas of an HTGR. 

Zirconium carbide is a highly refractory compound with excellent properties but, unlike titanium carbide, it has found only limited industrial importance except as coating for atomic-fuel particles (thoria and urania) for nuclear-fission power plants.l " ] This lack of applications may be due to its high price and difficulty in obtaining it free of impurities. 

Zirconium carbide also is a refractory compound [10]. The material has a melting point of 3450°C and is used as a coating for nuclear fuel particles such as Th02 and UO2 [10, 189, 190]. The compound is obtained by the CVD of a mixture of either ZrCU [189, 191] or ZrBr4 [190, 192] and methane (or propane) in the presence of hydrogen at 1000-1500 °C. 

The GT-MHR has very high proliferation resistance due to low fissile fuel volume fractions and the refractory characteristics of the TRISO fuel particle coating system that forms a containment from which it is difficult to retrieve fissile materials. 

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