INCEFA-PLUS delivers new experimental data and new guidelines for assessment of environmental fatigue damage to ensure safe operation of European nuclear power plants. Austenitic stainless steels will be tested for the effects of mean strain, hold time and material roughness on fatigue endurance. Testing will be in nuclear Light Water Reactor environments. The three experimental parameters were selected in the framework of an in-kind project during which the current state of the art for this technical area was developed. The data obtained will be collected and standardised in an online fatigue database with the objective of organising a CEN workshop on this aspect. The gaps in available fatigue data lead to uncertainty in current assessments. The gaps, will be targeted so that fatigue assessment procedures can address behaviour under conditions closer to normal plant operation than is currently possible. Increased safety can thus be assured. INCEFA-PLUS also develops and disseminates a modified procedure for estimating environmental fatigue degradation. This will take better account of the effects of mean strain, hold time and surface finish. This will enable better management of nuclear components, making possible the long term operation (LTO) of NPPs under safer conditions. INCEFA-PLUS is relevant to the NFRP1-2014 programme because: • Present guidance originates from NRC. In Europe various national programmes aim to develop counter proposals allowing greater operational efficiency with at least comparable safety assurance. INCEFA-PLUS brings these programmes together through which a strong EU response to the NRC methodology will be obtained with improved safety assurance through increased lifetime assessment reliability. • INCEFA-PLUS improves comparability of data from EU programmes because partner laboratories will do some tests on a common material under common conditions. Reduced assessment uncertainty will enable easier maintenance of safety