Abstract: Spent fuel multimodal transportation refers to the process of transporting spent fuel generated by nuclear power plants to reprocessing facilities or storage sites through multiple transportation modes (such as road, rail, waterway, etc.). The existing transportation system faces challenges such as data security, information silos, and difficult traceability. Based on the decentralized, traceable, and tamper-proof technologies of blockchain, this study adopts a domestic alliance chain architecture and domestic encryption algorithms to construct a "blockchain + internet of things" integration model, and proposes an IoT data trusted evidence storage and security protection scheme for spent fuel multimodal transportation that integrates core blockchain technologies. Three key innovations have been achieved: (1) In terms of architecture design, the alliance chain architecture with multi-node authorization combined with hierarchical national cryptographic algorithm dynamic encryption can effectively resist security threats such as brute-force cracking, data tampering, and man-in-the-middle attacks; (2) In terms of performance optimization, the "Practical Byzantine Fault Tolerance consensus + dynamic shard verification" mechanism is optimized, reducing the abnormal data verification delay to within 2 seconds and achieving a system throughput of 1200 TPS; (3) In terms of scenario application, a "Beidou + internet of things" millisecond-level data on-chain model has been developed to achieve trusted evidence storage throughout the lifecycle of key data such as radiation and location. Empirical studies show that this solution achieves a 100% tampering detection rate in terms of security, shortens the emergency response time from 83 minutes to 4 minutes, and reduces operational costs by approximately 30%. The research results provide the first engineering-implemented blockchain solution for high-radiation material transportation, which is of great practical significance for improving the safety management level of spent fuel transportation and promoting the digital transformation of the energy industry.