Fully Ceramic Microencapsulated (FCM) fuel which TRISO particles are dispersed in SiC matrix is evaluated to be able to dramatically improve the safety margin due to the high strength and thermal conductivity of the fuel materials. Since the effect of random particle distribution was not considered in most of modeling studies, a model for evaluating Thermal/Mechanical/Crack behaviors with random distribution of TRISO particle is developed. From the analysis results in PWR and SMR conditions, it is confirmed that the FCM fuel shows a symmetrical temperature/stress distribution in the FCM specification range of PF 40 to 50 % and kernel radius 300 to 400 microns. It is also confirmed that SiC matrix cracks are likely to be propagated form the inside of pellet rather than outside of pellet which is opposite tendency of $UO_2$ pellet. To reduce the possibility of crack propagation, high thermal conductivity kernel material such as UN should be used.