Summary of the NEA Assessment on Spent Nuclear Fuel Decay Heat for Light Water Reactors

This report summarises the NEA assessment of spent nuclear fuel (SNF) decay heat for light water reactors, which highlights the increasing importance of accurate decay heat estimations due to evolving fuel characteristics. Over the past decades, the nuclear industry has seen higher initial fuel enrichment, increased burn-up rates, and extended reactor cycle lengths. This necessitates a refined understanding of decay heat for safe handling, storage, reprocessing and disposal of SNF. Subgroup 12 (SG 12) of the NEA Working Party on Nuclear Criticality Safety (WPNCS) was established in 2022 to evaluate the accuracy of SNF decay heat predictions. The group examined experimental methods, computational models, and uncertainties in decay heat estimation and emphasised the need for new calorimetric measurements due to a lack of data for fuel types such as mixed oxide (MOX), water-water energetic reactor (VVER), and CANada Deuterium Uranium (CANDU).

This report’s recommendations include expanding experimental databases, improving theoretical models, and integrating machine learning (ML) for validation. Future studies will focus on enhancing simulation accuracy, reducing uncertainties, and refining safety assessments for long-term SNF management.