Fuel behaviour in low-temperature district heating reactor LDR-50 with fuel performance code finix.

LDR-50 design is an emerging small modular district heating reactor that is being developed in Finland. Fuel in the reactor will be operating at relatively low temperature compared to conventional LWR reactors (maximum temperature below 800 K and linear heat rates below 10 kW/m) which may present new phenomena.
The study aims to determine the relevance of certain phenomena, such as Fission Gas Release (FGR), cladding creep and fuel swelling under LDR conditions. The rod analysis in the reactor was carried out with VTT’s in-house FINIX fuel performance code to provide preliminary insights into fuel rod behaviour at low temperature. The analysis is based on the LDR lite model and realistic loading schemes of equilibrium cycles. The validity and application range of current models in FINIX was reviewed and the models were updated accordingly. Few modifications relevant to low temperature application have been implemented in FINIX.
The safety analysis shows that the anticipated risk profile of a shortened conventional fuel rod, at low-temperature SMR conditions is fairly neutral and uneventful. Proposed future work should focus on hydrogen pickup, corrosion and potential hardening impact in the cladding.