Improved fuel reliability means reduced fuel failures in reactor operation. Fuel failures, with their consequent adverse impact on the environment and requirements for additional waste management, result in costs for remediation, 'failed core' operation and maintenance. Therefore, poor performance of fuel can lead to uncompetitive operational conditions for a nuclear power plant. A revision of the earlier edition, this publication has been significantly extended to support nuclear fuel designers, manufacturers, reactor operators, and fuel engineers and managers on fuel design and design changes, fuel manufacturing, qualification, in-reactor operation, and on-site services to achieve excellence in fuel reliability and performance and safe operation of nuclear fuel under all applicable plant states.