Pin Type Geometry

The fuel pins used in the core are a new type for OCR s. The vast majority of OCR reactors use a TRISO type fuel embedded in a graphite matrix and are thermal neutron spectrum reactors. TRISO fuels are small UC spheres coated with layers of silicon carbide and pyrolitic carbon. While this results in fuels that can be used to extremely high bumup, the uranium density of the fuel is low. A coolant hole is then drilled through the blocks of fuel and these blocks are put in a prismatic array. 

The proposed reactor uses an array of UN pellet filled pins in a triangular pitch. These pins are clad in a layer of rhenium and NblZr. The use of rhenium limits the problem of nitrogen attack on NblZr. It also has positive accident safety characteristics. These pins are similar to those developed for the SP-100 program though they are used in a different reactor setup. 

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