Research of the spatial effect of PWR fuel pin with disperse particles

•The spatial effect of the double-heterogeneous FCM fuel in PWR is concluded.•The spatial effect of PWR fuel pin embedded with disperse BPPs is studied.•Sensitivity analysis on the packing fraction and size of kernel are performed.•Relevant neutronic parameters are detailly discussed and synthetically analyzed. Fully ceramic microencapsulated (FCM) fuel is one of the most popular accident tolerant fuels (ATF) and it has a particular spatial structure, made of SiC matrix embedded with TRISO fuel particles. Fuel pin embedded with disperse burnable poison particles, has similar spatial structure. They are both double-heterogeneous and they have much unique neutronic characteristic. In this paper, efforts are made to analyze how the spatial structure of the disperse fuel particles and burnable poison particles affects their neutronic behaviors in detail, from pin-cell level, which is also referred as spatial effect. Many important neutronic parameters are discussed, including infinite multiplication factor (Kinf), four factors (fast fission factor ∊, resonance escape probability factor p, thermal utilization factor f and thermal reproduction factor η), neutron flux level, nuclides number density. They are compared with an equivalent homogeneous structure and the corresponding differences would reveal the unique spatial effect of this kind of double-heterogeneous structure. Besides, sub-regions analyses are also carried on. Finally, it is proved that the double-heterogeneous spatial structure would bring much influence on neutronic behaviors, and the spatial effect of disperse burnable poison particles would be even more serious.