An equivalent thermal conductivity is described for core design of multi-hole type HTGR fuel. Thermal calculation of the complicated multi-hole fuel must deal with the two- or three-dimensional geometry. By certain simplication, the one-dimensional calculation is possible.
Fuel rods and coolant holes are distributed in a triangular array with ideal arrangement of two fuel rods and one coolant hole. A triangular unit cell with insulated boundaries is used as a typical fuel channel for core thermal calculation. A rod type fuel is substituted by the unit cell on the basis of the equivalent thermal conductivity of the ligament which is the graphite moderator between fuel holes and coolant hole in the unit cell.
Temperature distribution of the HTGR fuel unit cell is obtained by finite element method and the equivalent thermal conductivity is calculated from the unit cell temperature. General equation of the equivalent thermal conductivity is derived for the unit cell geometry composed of fuel hole, coolant hole and the pitch between.
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