Spent fuel storage has become an important component of spent fuel management options. As storage durations increase, spent fuel performance is a critical issue. This publication presents the results of an IAEA coordinated research project on this topic and contains useful information on the integrity and degradation of spent fuel during storage. The experience and insights provided by the participating countries will help Member States to identify challenges in implementing longterm storage and to understand the current status of spent fuel performance research related to longterm storage.