An evaluation of Dancoff factor for pebble-type reactor using method Monte Carlo method

Dancoff factor for pebble bed reactor is commonly evaluated by using Monte Carlo method. The calculation results of Dancoff factor can cause some errors due to the inaccurate geometry modeling of fuel kernels and pebbles. These are wall effect of fuel kernels, fuel kernel packing effect, and random mixture effect of fuel and moderator pebbles. The wall effect comes from the inaccurate number of fuel kernels adjacent to the boundary of fuel region. Packing Effect affects the result of Dancoff factor calculation caused by the selection of fuel kernel packing model. The random mixture effect of fuel and moderator pebbles is caused by the random position of fuel and moderator pebbles near source pebble. Therefore, it affects the results of inter-pebble Dancoff factor. These three effects are evaluated with the Monte Carlo method proposed in this study. The results can be utilized to evaluate the calculation error of Dancoff factor in using current available Monte Carlo codes. As a result, it can give a calculation criterion of Dancoff factor in using the Monte Carlo method. (authors)