Synergism of radiation and steam on mechanical properties of cable insulation removed from a nuclear power plant

ABSTRACT

A three-phase AC low-voltage cable insulated with flame-retardant ethylene-propylene-diene rubber (FR-EPDM), laid in a nuclear power plant (NPP) for 23 years, was removed. Several pieces of tubular insulation samples were obtained by removing the conductors out of the cable. For comparison, similar insulation samples were also prepared using a similar unaged cable and those aged artificially in different manners by the irradiation with gamma rays. In addition, the irradiation with gamma rays and exposure to steam, which simulated a plausible environment during a severe accident, were also given to some of those tubular samples. Tensile tests were performed to measure the elongation-at-break and tensile strength of those aged and unaged samples. As a result, it has become clear that the cable removed from the NPP did not severely deteriorate. In addition, it was found that the subsequent steam exposure can alleviate the mechanical degradation of FR-EPDM caused by the gamma-ray irradiation. The validity of the method to simulate the aging suffered in the NPP is discussed.

GRAPHICAL ABSTRACT

KEYWORDS:

• Degradation
• aging
• simulation
• gamma rays
• mitigation
• electrical insulation
• severe accident
• steam exposure
• tensile test
• polymer

Acknowledgments

The authors would like to thank the Kansai Electric Power Company, Inc., for sharing cable C1.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00223131.2023.2224371

Additional information

Funding

This research was performed under the research entrusted by the Secretariat of the Nuclear Regulation Authority in Japan.