Abstract：During the building of the first core of the pebble bed high-temperature gas-cooled reactor (PBR), the ratio between the fuel spheres and graphite spheres, the fill material in the gaps in the core and the cavity height above the pebble bed will change. Thus, the neutronics design of the first core using the deterministic VSOP code needs some special treatments. The approximations for the first are an evaluated using a more detailed model of the first core analyzed by a general Monte Carlo code. Comparisons of the predictions of the two codes show that the special treatments for the first core used with the VSOP code will not cause significant errors include using the equivalent sphere model to calculate the thermal spectrum, calculating the reactivity of the gap fill material using the streaming correction method, heating the helium atmosphere as a vacuum, and using anisotropic diffusion coefficients to model the large top cavity. Thus, these special treatments for the first core used by the VSOP code are acceptable.
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2017, Vol. 57 
