Strain-Based Acceptance Criteria for Inelastic Analysis

Abstract

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 cask vendors’ ability to perform non-linear impact analysis has improved, the need for a code-based method to interpret the results of this type of analysis has increased. The ASME Section III Working Group on Design of Division 3 Containments is working with Section III Working Group Design Methodology to develop strain-based acceptance criteria to use within the ASME Code for energy-limited events. This paper will briefly discuss the efforts within the ASME, detail the advantages of using strain-based criteria, discuss the problem areas associated with establishing strain-based criteria, and provide insights into inelastic analyses as applied to radioactive material transportation and storage casks in general. The views expressed represent those of the authors and not necessarily those of their respective organizations or the ASME.