PNNL

Abstract

Decabromodiphenyl ether (decaBDE) has been used as a flame-retardant additive in nuclear-grade electrical cable insulation. However, decaBDE has been identified as a persistent, bioaccumulative and toxic (PBT) substance, leading to regulatory scrutiny. On January 6, 2021, the Environmental Protection Agency (EPA) published a final rule to phase out decaBDE. The 2021 rule set a two-year compliance deadline for “processing and distribution in commerce of decaBDE for use in wire and cable insulation in nuclear power generation facilities.” In recognition of industry concerns following a sudden discontinuation of decaBDE-containing Class 1E wire and cable essential for nuclear power operations and the time needed for qualifying the individual components using the alternative insulation technology, an extended compliance deadline was set in the finalized amendments to the 2021 rule as published by the Environmental Appeals Board on November 12, 2024. The 2024 rule set the compliance deadline for processing and distributing decaBDE-containing wire and cable insulation until the end of the service life of these materials. Since decaBDE has long been relied upon as the flame retardant in one of the most common cross-linked polyethylene (XLPE) nuclear cable insulation formulations, RSCC Firewall III insulation, questions have naturally arisen regarding whether changes in cable performance might be expected for XLPE containing a decaBDE alternative, especially for safety-related cables that must perform their safety function in a design basis event such as a loss of coolant accident. The research described here directly investigates observable differences in material performance of the standard historical decaBDE-containing XLPE insulation and the newly-formulated XLPE containing a decaBDE alternative for samples subjected to accelerated thermal aging. Mechanical properties, thermal oxidative resistance, chemical structures, and discoloration of XLPE samples provided by the manufacturer with and without decaBDE were determined after various thermal and radiation aging conditions. Statistical analyses were performed to test the difference between samples of the two formulations in their measured properties. Key findings from this work include: • Statistically detectable differences between decaBDE-containing (XLPE-dBDE) and alternative formulation (XLPE-Alt) cables were found primarily under sequential aging conditions (T?R, R?T) and thermal-only aging, particularly in yellowness, Fourier-Transform Infrared spectrometetry (FTIR) response, and mass change metrics. For other material properties such as tensile elongation and carbonyl index, no statistically significant difference was found between the two formulations. • Antioxidants were effectively protecting the material from thermal degradation, but less effectively consumed during radiation-only aging. • “Inverse temperature effect” (ITE) observed during radiation-only aging at for some samples which were highly brittle (elongation at break [EAB]