(223a) Understanding the Effects of Gamma Radiation on the Chemical and Physical Characteristics of Potential Coolants for Organic Cooled Reactors

Existing light water reactors may be replaced by a variety of advanced reactor concepts, many of which have faced significant challenges due to material limitations at high temperatures. The organic-cooled nuclear concept is an appealing design because it permits operation at pressures close to atmospheric pressure, due to its high boiling point and the use of less expensive carbon steel and zirconium alloys as core materials. Two candidate organic fluids, Dowtherm A (73% Biphenyl ether: 27% Diphenyl) and Paratherm HT (80% Hydrogenated terphenyl: 20% Terphenyl) have been investigated; as such an understanding of how their thermo-physical and chemical properties evolve under irradiation is required. In the present study, we irradiate these organic fluids under a Co-60 gamma irradiation source, accumulating a total absorbed dose of 30 MGy at room temperature (298 K) and 573 K. We then compare the changes in thermal conductivity, heat capacity, viscosity, contact angle, and surface tension before and after gamma irradiation. To further interpret changes in the physical properties, the structural, ionic activity, and compositional changes are also characterized using UV-Vis, FTIR, GC-MS, and electrochemical potential measurement. Preliminary results suggest insignificant changes in the material properties of the organics at room temperature.