PSI - Issue 77

Enrique Gómez et al. / Procedia Structural Integrity 77 (2026) 49–55 Enrique Gómez et al. / Structural Integrity Procedia 00 (2026) 000–000

50 2

service temperature (known as LST, Lowest Service Temperature) of -40°C. This extremely cold external environment requires an assessment of brittle fracture failure in the materials used in this type of cask.

Figure 1. Schematic of ENUN cask (https://www.ensa.es/contenedores/)

In the forges constituting the containment barrier, whose thickness is increased due to shielding requirements, the assessment of brittle fracture conditions can be performed according to ASME III Division 3, Subsection WB (2023). The design part of this subsection of the ASME Code establishes the need to verify protection against brittle fracture, and the materials part of the Code provides an acceptance criterion based on the determination of the reference ductile to-brittle transition temperature (RT NDT ) required from the forge manufacturer. This temperature, which is the highest temperature that produces brittle fracture according to standardized impact tests performed on the material, is obtained from the LST and a safety factor (which depends on the component thickness) with a high degree of conservatism. As an alternative to such approaches, and based on the dispositions gathered in IAEA Safety Standards No. SSG 26 (2018) concerning the assessment of fracture conditions, this work proposes a structural integrity analysis methodology based on the BS7910 (2019) and the corresponding use of Failure Assessment Diagrams. As an example of this methodology, the analysis has been performed here in the inner shell of an ENUN cask. The work is a preliminary step to the activities to be developed within the framework of the COSME project, whose main objective is to evaluate and rule out non-ductile fracture failure in the containment barrier of ENUN casks by using both the fracture mechanics criteria included in Sections III and XI of the ASME Code and the real mechanical properties of the cask materials (forge and welds). 2. Materials and methods 2.1. Material The tensile properties of the forging material (steel SA-350 LF3 Class 2) have been obtained from ASME Section II, Part D (2023), and are shown in Table 1 (σ Y : yield stress; σ u : tensile strength; E: elastic modulus): Table 1. Material properties. Material σ Y (MPa) at -40°C σ u (MPa) at -40°C E (MPa) at -40°C K mat (MPam 1/2 ) at -40°C

SA-350 LF3 Class 2

259.0

482.6

194900

73.66