A Practical Model for Prediction of the Lifetime of Elastomeric Seals in Nuclear Environments

Volume II: near-field and altered-zone environment report

“…Polymer degradation occurs by one of two primary structural changes: cross-linking or chain scission. Models have been developed to predict specific degradation processes over times significant to a radioactive waste repository (Burnay, 1990) however most models are for normal life times and under normal service conditions (Kenny, 1993). An activation energy must be reached before degradation begins (Ravanetti and Zini, 1992) which can be derived from thermal analysis.…”

“…It has been found that thermal degradation rate is increased by higher temperatures, the presence of a radiation flux, oxidative agents, some chemical contaminantts and light. In addition, many polymers can exhibit dose rate effects or synergism between radiation and temperature or chemical contamination (BUrnay, 1990).…”

Performance Evaluation of O-Ring Seals in Model 9975 Packaging Assemblies (U)

“…Burnay and other investigators continued to refine the superposition approach in order to develop a predictive model of radiation degradation in elastomeric materials [36,37]. Based on the previous model, thermal and dose shift factors for individual effects were combined into a single shift factor a(T, D) to be used to superpose data at different dose levels and temperatures.…”

“…[12,14,25,[36][37][38][39][40][41][42]. Compression set is generally defined as the amount of permanent deformation or recovery lost following a specified amount of deflection or applied load [14].…”

“…The permeability of gas through an elastomer depends upon many factors, including but not limited to cross-link density, polymer type/structure, percent squeeze or compression, temperature, and gas molecular weight [12,14,36,41,48]. As cross-link density and other properties which control permeability are directly dependent upon formulation and compounding, permeability is considered to be highly compoundspecific.…”