Hydrogen and hydrazine co-injection to mitigate stress corrosion cracking of structural materials in boiling water reactors, (VI) the effect of ammonia on intergranular stress corrosion cracking

Hydrogen and hydrazine co-injection into a boiling water reactor was considered as a new mitigation method of stress corrosion cracking (SCC). In this method, some amount of ammonia will be formed by the decomposition of hydrazine. The effect of ammonia on SCC susceptibility was studied over a wide range of electrochemical corrosion potentials (ECPs) in 288 degrees C water by conducting slow strain rate technique SCC experiments (SSRTs). ECP was changed from -0.6 V versus the standard hydrogen electrode (V(SHE)) to 0.1 V(SHE) by controlling dissolved oxygen concentration. Ammonia concentration was controlled to have values of 100 and 530ppb. Similarly, sulfuric acid was injected to confirm the difference in the effect of injected chemical compounds on SCC susceptibility. The intergranular stress corrosion cracking (IGSCC) fraction, which was used as the index of SCC susceptibility, decreased with decreasing ECP for the case of no chemical injection. Sulfuric acid enhanced the IGSCC fraction. These data were in good agreement with literature data. On the other hand, ammonia at less than 530ppb did not affect IGSCC fraction. It is expected that 51-280 ppb hydrazine and 0-53 ppb hydrogen will be injected into reactor water to mitigate SCC in BWRs. In the bottom region of the reactor pressure vessel, ECP and ammonia concentration will be -0.1 V(SHE) and 15-60ppb, respectively. Under these conditions, ammonia did not affect SCC susceptibility. So SCC susceptibility will be mitigated by decreasing the ECP using hydrazine and hydrogen co-injection.