Hydrazine and hydrogen co-injection to mitigate stress corrosion cracking of structural materials in boiling water reactors, (1). Temperature dependence of hydrazine reactions

Hydrazine and hydrogen co-injection into reactor water is considered a new mitigation method of stress corrosion cracking in BWRs. Fundamental data such as the thermal decomposition of hydrazine, the reaction of hydrazine with oxygen and with hydrogen peroxide at temperatures ranging from 150 to 280degC are needed to evaluate suitability of this method. Reactions in bulk water were studied in a polytetrafluoroethylene pipe to separate surface reaction effects. The results were as follows. (1) The orders of the apparent reaction rate of hydrazine with oxygen were 1 and 0.5 for hydrazine and oxygen concentrations, respectively (- dC_N2H4/dt=- dC_O2/dt=kC_N2H4C_O2^0.5). Arrhenius parameters were k₀=69.0 s^-1·μM^-0.5 and E_a=43.0 kJ·mol^-1 (k=k₀ exp(- E_a/RT)). (2) The orders of apparent reaction rate of hydrazine with hydrogen peroxide were each 0.5 for hydrazine and hydrogen peroxide concentrations (- dC_N2H4/dt=kC_N2H4^0.5C_H2O2^0.5). Arrhenius parameters were k₀=1.42x10⁶ s^-1, E_a=78.8 kJ·mol^-1. Based on these data, the applicability of hydrazine and hydrogen co-injection into BWRs was considered. Hydrazine introduction to reactor water was confirmed to be accompanied by only 1% decomposition. The concentration of oxygen, which is injected to suppress the flow-assisted corrosion of carbon steel in current BWR operation, would decrease due to the reaction of hydrazine with oxygen. However oxygen concentration in feed water could be maintained at the required level if the concentration of oxygen injected in condensate water was at most doubled compared to the current operating concentration. (author)