TN® 24 Dual Purpose Casks: 20 years of Licensing Experience

The TN® 24 cask family is composed of dual purpose casks designed and licensed for both transport and dry storage in various countries such as France, Germany, Belgium, Switzerland, Italy, the United States and Japan. The TN® 24 casks have been loaded with various PWR and BWR fuel assemblies for more than 20 years. The licensing capability of dual purpose casks for their entire lifetime is key to guaranteeing a long term solution for dry storage of fuel assemblies. For the TN® 24 such capability is based on a solid cask design with a containment shell made of thick carbon steel forging and narrow gap weld and supported by robust safety demonstrations and material qualifications.The safety demonstrations addressed complex phenomena, especially for mechanical analysis of the containment body under very stringent accident conditions such as 9-meter drop tests, military aircraft crash impact directly on cask, and resistance to brittle fracture at -40°C. The key elements ensuring the safety performance of the TN® 24 are the following:• The qualification of the forging and welding processes and associated non-destructive tests: The methods for qualification of the manufacturing processes are performed with an extended mechanical test program to define the most vulnerable area of the forging and containment weld. In the same manner, the performance of the Non Destructive Tests (NDT) is essential to prevent the risk of brittle fracture. The NDT should detect the expected surface and volumic defects of the forging and welding process.• Advanced experimental drop and crash tests demonstrating the leak-tightness of the cask with direct measurement of the helium leak-rate before and after tests: These tests are used for both safety demonstrations and benchmarks for numerical calculations. These benchmarks ensure the deep understanding of these complex phenomena and a reliable capability to accurately assess the cask safety margins.The purpose of this document is to present the basis of the TN® 24 cask safety performance and associated qualification methodology through relevant examples issued from 20 years of licensing.