The New ASME Section III, Division 3 Strain-Based Acceptance Criteria and Computational Modeling Guidance Document

Nuclear material transportation and storage casks are designed to resist a number of hypothetical accident events. Hypothetical accidents considered for transport packages include a 9-meter free drop onto an unyielding target and a 1-meter free fall onto a puncture spike. For storage casks, accident conditions include drops, tip-over, and aircraft impact. All of these accident events are energy-limited rather than load-limited. Therefore, it makes sense to have analysis acceptance criteria that are more closely related to absorbed energy than to applied load. The new Section III, Division 3 strain-based acceptance criteria are the best way to meet this objective. Today explicit dynamics finite element computer codes are sufficiently sophisticated and robust to produce accurate results for energy-limited events. However, there appears to be a lack of clear guidance within the user community as to what constitutes the computational modeling requirements necessary to achieve accurate results. To address this issue the Code specifies that the strain-based criteria can only be applied to results obtained from a “Quality Model,” which is defined as a model that adheres to the guidance set forth in the ASME Computational Modeling Guidance Document for Explicit Dynamics (currently being developed), or has been developed with the aid of suitable convergence and sensitivity studies. This paper discusses the new strain-based criteria and the Computational Modeling Guidance Document.