CSR behavior and aging model for the Viton© Fluorelastomer O-rings in the 9975 shipping package

Abstract

The 9975 Type B shipping package is used within the DOE complex for shipping special nuclear materials. This package is re-certified annually in accordance with Safety Analysis Report for Packaging (SARP) requirements. The package is also used at the Savannah River Site as part of the long-term storage configuration of special nuclear materials. As such, the packages do not undergo annual recertification during storage, with uncertainty as to how long some of the package components will meet their functional requirements in the storage environment. The packages are currently approved for up to 15 years storage, and work continues to provide a technical basis to extend that period. This report describes efforts by the Savannah River National Laboratory (SRNL) to extend the service life estimate of Viton ® GLT and GLT-S fluoroelastomer O-rings used in the 9975 shipping package. O-rings of both GLT and GLT-S compositions are undergoing accelerated aging at elevated temperature, and are periodically tested for compression stress relaxation (CSR) behavior. The CSR behavior of O-rings was evaluated at temperatures from 175 to 400 °F. These collective data were used to develop predictive models for extrapolation of CSR behavior to relevant service temperatures (< 156 °F). The predictive model developed from the CSR data conservatively indicates a service life of approximately 37 years for Viton GLT O-rings at the maximum effective service temperature of 156 °F. The estimated service life for Viton GLT-S O-rings is significantly longer.

Compression Stress-Relaxation and Oxygen Consumption Behavior of 9975 Shipping Package O-rings

“…Aging and oxygen consumption testing will continue for GLT-S O-ring samples at 73 to 250 °F. [8]. Additional data has been collected and the cumulative data set through February 2018 is presented in this report.…”

SDU7 Interior Liner Testing & Evaluation

“…For liner service life prediction, a broader testing approach could be performed as done for longlife polymeric components such as nuclear reactor electrical cable insulations, HDPE geomembranes/piping, radioactive waste containment packaging and elastomeric O-rings in critical applications [44][45][46][47][48].…”

9975 Shipping package component long-term degradation rates

“…The samples aged at ≥300 °F have reached the end-of-life criterion, while data from the lower temperature samples have been extrapolated to the end-of-life criterion through timetemperature superposition (TTS) (see Figure 1). Reference [3] summarizes this data and develops a basis to predict service life at lower temperatures using the time-temperature superposition principle. This approach can be applied to estimate the service life for O-rings at 135 °F, as follows.…”

“…Using this approach for GLT O-rings (calculated activation energy of 60 kJ/mol, and ~19 years to reach the end-of-life criterion at 175 °F [3]), the estimated time to reach the end-of-life criterion at 135 °F is about 77 years. Figure 2).…”