Strain-Based Acceptance Criteria for Spent Fuel Storage and Transportation Containments - Presentation

Modern finite element codes used in the design of nuclear material transportation and storage casks can readily calculate the response of the packages beyond the elastic regime. These packages are designed to protect workers, the public, and the environment from the harmful effects of the transported radioactive material following a sequence of hypothetical accident conditions. Hypothetical accidents considered for transport packages include a 9-meter free drop onto an essentially unyielding target and a 1-meter free fall onto a 30-cm diameter puncture spike. For storage casks, accident conditions can include drops, tip-over, and aircraft impact. All of these accident events are energy-limited rather than load-limited, as is typically the case for boilers and pressure vessels. Therefore, it makes sense to have analysis acceptance criteria that are more closely related to absorbed energy than to applied load. Strain-based acceptance criteria are the best way to meet this objective. As computational tools have improved cask vendors’ ability to perform non-linear impact analysis, the need for a code-based method to interpret the results of this type of analysis has increased, and in 2006 the NRC encouraged ASME to develop strain-based criteria for energy-limited events. The ASME Section III Working Group on Design of Division 3 Containments has been working with the Section III Division 1 Working Group on Design Methodology to develop such a strain based criteria to use within the ASME Code Section III, Division 3 for energy limited events. An important aspect of the strain-based criteria is that it can only be applied to a “Quality Model:” where a Quality Model is defined as a model that adheres to the guidance set forth in the ASME Computational Modeling Guidance Document for Explicit Dynamics Software (currently being developed by the Task Group on Computational Modeling for Explicit Dynamics), or has been developed with the use of convergence and sensitivity studies. This paper will briefly discuss the proposed ASME Strain-based criteria, detail the advantages of using strain-based criteria, and discuss the problem areas associated with establishing strain-based criteria.