First Barrier the Nuclear Fuel Matrix

The nuclear fuel most commonly used in NPPs is ceramic UO2 peUets with different levels of enrichment. In comparison with other fuel materials, this matrix 

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The first three physical barriers are the fuel matrix, the fuel cladding and the boundary of the primary coolant system. All nuclear power plants now operating or under consideration have all of these barriers some gas-cooled reactors also have another barrier in the form of a graphite moderator into which fuel particles with a graphite or ceramic coating are embedded. 

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