Organic-cooled reactor concepts offer potential advantages over traditional light water reactors, including operation at elevated temperatures and reduced pressures. However, radiation-induced degradation of organic coolants remains a critical concern requiring thorough investigation. This study examines the effects of gamma irradiation (1-MGy dose) on Dowtherm A (27% biphenyl, 73% diphenyl ether) under varying atmospheric conditions (ambient air versus argon) and temperatures (room temperature versus 250°C).

Chemical characterization using Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), and gas chromatography-mass spectrometry revealed the formation of higher molecular weight byproducts, including terphenyls and quaterphenyls, along with notable biphenyl degradation. Physical property measurements using differential scanning calorimetry, rheometry, and thermal conductivity analysis demonstrated significant changes in the thermophysical properties, including decreased heat capacity and viscosity, with increased thermal conductivity observed under argon irradiation conditions.

Pronounced photodarkening occurred in all the irradiated samples, with atmospheric conditions significantly influencing degradation pathways. UV-Vis analysis indicated that oxygen presence during irradiation suppresses certain chromophoric species formation. These findings provide crucial insights into radiation-induced degradation mechanisms and their impact on coolant performance, informing future organic coolant system design and optimization strategies for advanced reactor applications.