Assessment of Calculation Model for Annular Core on the HTTR

It was shown from the annular core critical experiment of the HTTR that its excess reactivity values tend to be overestimated about 3%Δk/k by the HTTR core design method. Therefore, assessment of the calculation model for the annular core of the HTTR was systematically undertaken. The revised model was investigated which was based on the SRAC code system. It was concluded that the multiplication factor of the annular core is considerably affected by the three factors listed below: (1) The Benoist's anisotropic diffusion coefficients (2) The mesh interval in the whole core diffusion calculation (3) The mesh structure of graphite region in fuel lattice cells. The significantly large discrepancy previously reported was reduced down to 1.6%Δk/k by the revised annular core model.