Burnup analysis of the pebble-bed fluoride-salt-cooled high-temperature reactor based on the Chord Length Sampling method

•CLS method with modified packing fraction correction for the PB-FHR is implemented.•The differences between CLS method and explicit modeling method are analyzed.•The CLS method with a modified packing fraction correction was adopted. The neutronics calculation of the PB-FHR with the fraction ranging from 5% to 30% are carried out by the CLS method and ERM method. It can be observed that the infinite multiplication factor obtained with the CLS method are consistently smaller than those obtained with the ERM method when the fraction is less than 15%. Moreover, the differences of the two methods basically increases with the increasing burnup level when the fraction is less than 15%. For the fraction up to 30%, the CLS method shows significant bias of 520 pcm with the explicit method. After the CLS method with a modified packing fraction correction is adopted, the largest difference drops to 220 pcm when the fraction is 30%.