[en] This report describes the results of integrity assessment of the HTTR fuel as a part of safety design of the reactor. Functions of individual coating layer of the coated fuel particles were investigated to clarify the characteristic properties of the HTTR fuel. Integrity of the fuel under normal operating conditions of HTTR was shown to be maintained through analyses on fuel failure and due to kernel migration (amoeba effect) and corrosion of the silicon carbide layer by palladium. The fuel integrity has been demonstrated by successful results of the irradiation performance tests. By considering the failure behavior of coated fuel particles, the permissible design limit of the fuel was determined such that the fuel temperature should not exceed 1600degC under abnormal transient conditions. The validity of the determination of the limit has been confirmed by results of heating experiments of coated fuel particles at extremely high temperature. (author)