Performance of Bolted Closure Joint Elastomers Under Cask Aging Conditions

The bolted closure joint of a bare spent fuel cask is susceptible to age-related degradation and potential loss of confinement function under long-term storage conditions. Elastomeric seals, components of the joints typically used to facilitate leak testing of the primary seals that include the metallic seal and bolting, are susceptible to degradation over time by several mechanisms, principally thermo-oxidation, stress-relaxation, and radiolytic degradation. Irradiation and thermal exposure testing and evaluation of an ethylene-propylene diene monomer (EPDM) elastomeric seal material similar to that used in the CASTOR^®1 V/21 cask. Testing covers a matrix of temperature and radiation exposure conditions relevant to extended storage of the cask. Semi-empirical models are being developed to predict loss of sealing force. A special insert was developed to allow Compressive Stress Relaxation (CSR) measurements before and after the irradiation and/or thermal exposure without unloading the elastomer. A condition of the loss of sealing force for the onset of leakage was suggested. The experimentation and modeling being performed could enable acquisition of extensive coupled aging data as well as an estimation of the time when loss of sealing under aging (temperature/radiation) conditions may occur.