[en] Recently, the sea transport of the nuclear fuel materials are playing important role in Japan. However several years ago, some opinions referring to validity of thermal test requirement for packages were raised. Therefore in 1996-98, IAEA carried out a Co-ordinated Research Programme (CRP) for studying the propriety of the thermal test during the sea transport of the packages. Under such background, in 1996-1999 the Shipbuilding Research Association of Japan carried out the safety assessment for fire accidents of nuclear fuel material packages during the sea transport. This paper deals with results of the study, integrity of packages for high-level radioactive waste in case of engine room fire accidents. It was clarified that integrity of packages can be kept under the hypothetical severest conditions. (author)