Abstract: In-pile irradiation facility design of ceramic pebble bed assembly and irradiated scenario could be improved with physical calculation and analysis. According to the experimental and technical requirement of in-pile irradiation, tritium production, rate of tritium production and nuclear heat were calculated for ceramic pebble bed assembly in different vertical tubes with MCNP code. The results show that the pebble bed assembly with natural enrichment of ⁶Li which is irradiated in test tube with half power or with full power at the location of 23 cm above reactor core mid-plane could satisfy the experimental and technical requirement.