Calculation of the Macroscopic Group Constant of Pebble Bed Fluoride Salt Cooled High Temperature Reactor Based on the Collision Probability Method

The pebble bed fluoride salt cooled high temperature reactor (PB-FHR) is one of the generation IV nuclear reactors, a lot of study has concentrated on PB-FHR neutronics all over the world. As the most important part in the study work, the macroscopic group constant must be well prepared. The fuel pebble was chosen for the candidate of PB-FHR due to its outstanding, but the double heterogeneous due to its complex structure causes much difficult in the calculation of macroscopic group constant. In this work, an analytical program named Z2D is written to calculate the macroscopic group cross section. In the program, the collision probability method (CPM) was applied to solve the slowing-down integral transport equation, and the macroscopic constant was evaluated with the obtained neutron flux. Also, the recurrence method was introduced to accelerate the computing speed of slowing-down source. The results were compared with those calculated by MCNP, and good agreements were obtained.