End of life management of radioactive sources is an important aspect of radiological security. Radioactive sources must be safely and securely controlled throughout their lifecycle. Disused sources are at higher risk of falling out of operational and regulatory control than sources still in use. Centralized, secure storage decreases the risk that the sources could be neglected, diverted, or lost. There is a need for additional back-end management tools to support the safe and secure disposition of radioactive sources. An optimized Silo Storage System (S3) for long-term interim storage has been developed based on many decades of silo storage technical and operational experience. Silo storage provides an economical solution that meets international standards while being modular and flexible in nature to meet the unique needs of each user country. A standard design package has been developed to support partners that are interested in collaboration.