Decomposition of hydrogen peroxide in high-purity water has been measured at temperatures ranging 100 to 280°C in a laboratory test loop. A first-order decomposition kinetics has been observed in all cases, but the decomposition rates were found to vary widely, depending on the material used in the reaction chamber. In a 4 mm ID stainless steel tubing, the decomposition rate constant is determined to be k = 2 x lo5 exp(-14800/RT). This decomposition rate is approximately 100 times faster than that observed in a Teflon tubing.The variation of decomposition rate in different reaction chambers is attributed to the heterogeneous catalytic effects. There is no evidence of reaction between HP and HzOz in the highpurity water at temperatures up to 280°C.

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The effects of gamma-ray irradiation and sodium sulfate as an aqueous impurity on the intergranular stress corrosion cracking (IGSCC) susceptibility of sensitized type 304 (UNSI' ) S30400) stainless steel (SS) were studied through slow strain rate tests (SSRT) and corrosion potential measurements in high-temperature water that simulated the BWR normal water chemistry (NWC) and hydrogen water chemistry (HWC) conditions. The SSRT results demonstrated that IGSCC was accelerated by gamma-ray irradiation under the NWC condition, while it was suppressed under the HWC condition. These different effects are attributable to the radiation-induced corrosion potential shifts in the opposite directions depending on the water chemistry condition. When the sodium sulfate was injected up to 0.32 p.S/cm of conductivity, IGSCC was observed even under the HWC condition, but it was suppressed by gamma-ray irradiation.