skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Progress in Characterizing Thermal Degradation of Ethylene-Propylene Rubber

Abstract

Ethylene-propylene rubber (EPR) is one of the two most common nuclear cable insulation materials. A large fraction of EPR-insulated cables in use in the nuclear industry were manufactured by The Okonite Company. Okoguard® is the name of the medium voltage thermoset EPR manufactured by The Okonite Company. Okoguard® has been produced with silane-treated clay filler and the characteristic pink color since the 1970’s. EPR is complex material that undergoes simultaneous reactions during thermal aging including oxidative and thermal cleavage and oxidative and thermal crosslinking. This reaction complexity makes precise EPR service life prediction from accelerated aging using approaches designed for single discreet reactions such as the Arrhenius approach problematic. Performance data and activation energies for EPR aged at conditions closer to service conditions will improve EPR lifetime prediction. In this report pink Okoguard® EPR insulation material has been thermally aged at elevated temperatures. A variety of characterization techniques have been employed to track material changes with aging. It was noted that EPR aged significant departure in aging behavior seemed to occur at accelerated aging temperatures between 140°C and 150°C at around 20 days of exposure. This may be due to alternative degradation mechanisms being accessed at this higher temperature andmore » reinforces the need to perform accelerated aging for Okoguard® EPR service life prediction at temperatures below 150°C.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1406831
Report Number(s):
PNNL-25713; M3LW-16OR0404014
830403000
DOE Contract Number:
AC05-76RL01830
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; cables; npp; epr; thermal; degradation; aging

Citation Formats

Fifield, Leonard S., Huang, Qian, Childers, Matthew I., Correa, Miguel, Shin, Yongsoon, and Zwoster, Andy. Progress in Characterizing Thermal Degradation of Ethylene-Propylene Rubber. United States: N. p., 2016. Web. doi:10.2172/1406831.
Fifield, Leonard S., Huang, Qian, Childers, Matthew I., Correa, Miguel, Shin, Yongsoon, & Zwoster, Andy. Progress in Characterizing Thermal Degradation of Ethylene-Propylene Rubber. United States. doi:10.2172/1406831.
Fifield, Leonard S., Huang, Qian, Childers, Matthew I., Correa, Miguel, Shin, Yongsoon, and Zwoster, Andy. 2016. "Progress in Characterizing Thermal Degradation of Ethylene-Propylene Rubber". United States. doi:10.2172/1406831. https://www.osti.gov/servlets/purl/1406831.
@article{osti_1406831,
title = {Progress in Characterizing Thermal Degradation of Ethylene-Propylene Rubber},
author = {Fifield, Leonard S. and Huang, Qian and Childers, Matthew I. and Correa, Miguel and Shin, Yongsoon and Zwoster, Andy},
abstractNote = {Ethylene-propylene rubber (EPR) is one of the two most common nuclear cable insulation materials. A large fraction of EPR-insulated cables in use in the nuclear industry were manufactured by The Okonite Company. Okoguard® is the name of the medium voltage thermoset EPR manufactured by The Okonite Company. Okoguard® has been produced with silane-treated clay filler and the characteristic pink color since the 1970’s. EPR is complex material that undergoes simultaneous reactions during thermal aging including oxidative and thermal cleavage and oxidative and thermal crosslinking. This reaction complexity makes precise EPR service life prediction from accelerated aging using approaches designed for single discreet reactions such as the Arrhenius approach problematic. Performance data and activation energies for EPR aged at conditions closer to service conditions will improve EPR lifetime prediction. In this report pink Okoguard® EPR insulation material has been thermally aged at elevated temperatures. A variety of characterization techniques have been employed to track material changes with aging. It was noted that EPR aged significant departure in aging behavior seemed to occur at accelerated aging temperatures between 140°C and 150°C at around 20 days of exposure. This may be due to alternative degradation mechanisms being accessed at this higher temperature and reinforces the need to perform accelerated aging for Okoguard® EPR service life prediction at temperatures below 150°C.},
doi = {10.2172/1406831},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 8
}

Technical Report:

Save / Share:
  • Samples of fluorinated ethylene propylene copolymer thermal blanketing material, recovered from the Long Duration Exposure Facility (LDEF), were investigated to determine the nature and the extent of degradation due to exposure to the low-Earth-orbit environment. Samples recovered from the ram-facing direction of LDEF, which received vacuum-ultraviolet (VUV) radiation and atomic-oxygen impingement, and samples from the trailing edge, which received almost exclusively VUV exposure, were investigated by scanning electron microscopy and atomic force microscopy. The most significant result of this investigation was found on samples that received only VUV exposure. These samples possessed a hard, embrittled surface layer that was absentmore » from the atomic-oxygen exposed sample and from unexposed control samples. This surface layer is believed to be responsible for the 'synergistic' effect between VUV and atomic oxygen. Overall, the investigation revealed dramatically different morphologies for the two samples. The sample receiving both atomic-oxygen and VUV exposure was deeply eroded and had a characteristic 'rolling' surface morphology, while the sample that received only VUV exposure showed mild erosion and a surface morphology characterized by sharp high-frequency peaks. The morphologies observed in the LDEF samples, including the embrittled surface layer, were successfully duplicated in the laboratory.« less
  • The role of formulation on the severity of water treeing in EPR cable insulation was investigated using test cells where the insulation was sandwiched between two layers of semiconducting shields. The cells were exposed to a nominal electric stress of 85 V/mil at room temperature, while subjected to an environment of distilled, deionized water. Four base polymers differing in Mooney viscosity and ethylene content were modified by addition of various amounts of clay, red lead (ion scavenger) and crosslinking agent (dicumyl peroxide), and different processing aids and antioxidants. The equivalent vented tree length and count as well as the maximummore » bowtie tree length were considered as the dependent variables. The results were analyzed statistically by the best subsets regression method, producing single variable fits and two-variable interactions. A number of graphs were generated, relating treeing trends to the ingredients used in the formulations. In another set of experiments, the effects of filler dispersion (agglomeration), clay particle size, clay surface treatment and addition of ethylene were investigated using the laboratory accelerated water treeing test and a number of diagnostic tests, such as time-domain dielectric spectroscopy (TDDS), thermally stimulated discharge current (TSDC) and others.« less
  • This report presents the findings of the Chemical Compatibility Program developed to evaluate plastic packaging components that may be incorporated in packaging mixed-waste forms for transportation. Consistent with the methodology outlined in this report, the author performed the second phase of this experimental program to determine the effects of simulant Hanford tank mixed wastes on packaging seal materials. That effort involved the comprehensive testing of five plastic liner materials in an aqueous mixed-waste simulant. The testing protocol involved exposing the materials to {approximately}143, 286, 571, and 3,670 krad of gamma radiation and was followed by 7-, 14-, 28-, 180-day exposuresmore » to the waste simulant at 18, 50, and 60 C. Ethylene propylene diene monomer (EPDM) rubber samples subjected to the same protocol were then evaluated by measuring seven material properties: specific gravity, dimensional changes, mass changes, hardness, compression set, vapor transport rates, and tensile properties. The author has determined that EPDM rubber has excellent resistance to radiation, this simulant, and a combination of these factors. These results suggest that EPDM is an excellent seal material to withstand aqueous mixed wastes having similar composition to the one used in this study.« less
  • The flammability characteristics of ethylene propylene and chlorosulfonated polyethylene rubbers containing fire-retardant additives, aged in different thermal and radiation environments have been studied. Flammability parameters for these materials (time to ignition, mass pyrolysis, buring rate and fuel consumption) when exposed to, and aged in thermal, radiation, and thermal/radiation environments are discussed. Two formulations of each type of rubber are compared. The results are a direct contradiction to expected results based on small-scale flammability tests. They show that the fire-retarding agents used in this investigation do not reduce, and in some cases, contribute to, rubber flammability when exposred to a full-scalemore » fire environment. In addition, the results show that for full-scale fire conditions, the energy required for ignition of chlorosulfonated polyethylene is lower than that required for ethylene propylene rubber; a complete reversal of expected results. The effects of aging on the tensile-elongation properties have been determined. Radiation dose-rate effects are also discussed. Results show that the fire-retardant additives have a negligible influence on the tested materials' tensile-elongation properties and on material aging, regardless of the aging environment. The data obtained, however, may be too limited to show significant dose-rate effects. 15 figures, 9 tables.« less