Hydrazine and Hydrogen Co-injection to Mitigate Stress Corrosion Cracking of Structural Materials in Boiling Water Reactors, (II) Reactivity of Hydrazine with Oxidant in High Temperature Water under Gamma-irradiation

Abstract

Hydrogen and hydrazine co-injection into a boiling water reactor was considered as a new mitigation method of stress corrosion cracking. To confirm decrease of electrochemical corrosion potential by the reduction of oxygen and hydrogen peroxide in bulk water using reducing agent, reaction of hydrazine with oxygen or hydrogen peroxide under simulated downcomer conditions (temperature: 280 C, duration: 4.2 s and gamma-irradiation) was examined. All the oxygen was consumed above the equivalent concentration for the reaction with oxygen within this short time (gammairradiation case) and almost all the hydrogen peroxide was consumed. Reaction rates were accelerated more than five times by gamma-irradiation in each case. Reaction rates with oxygen were compared with other reducing agents such as hydrogen, methanol and ammonia. From the viewpoint of reaction rate and formation of by-product, hydrazine was the most suitable agent. Using a simple model based on the experimental results, water chemistry for the bottom region was calculated for the case of no hydrogen injection and for the case of 0.2 mmolÁkg À1 hydrogen injection into feed water. For both cases, concentrations of dissolved oxygen and hydrogen peroxide were estimated to decrease enough to mitigate SCC, with concentration of ammonia suppressed below the management criteria for reactor water chemistry.

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

“…2) In the bottom region of the RPV, ECP and ammonia concentration will be À0:1 V(SHE) and 15-60 ppb, respectively. 2) Even though all of the injected hydrazine decomposes into ammonia according to Eq.…”

“…[3][4][5][6] The ammonia concentration was two or ten times as large as the ammonia concentration formed in the bottom region of the RPV by hydrazine and hydrogen co-injection. 2) The sulfuric acid concentration used had the same EC (130 mSÁm À1 ) as the 100 ppb ammonia solution. …”

“…1). 1,2) Hydrazine and hydrogen react with oxygen and with hydrogen peroxide in the downcomer, according to the following net reactions (Eqs. (1)-(4)) and ECP decreases below À0:1 V versus the standard hydrogen electrode (V(SHE)) in the bottom region of the reactor pressure vessel (RPV).…”

Hydrazine and Hydrogen Co-injection to Mitigate Stress Corrosion Cracking of Structural Materials in Boiling Water Reactors (IV)

“…Therefore, we selected hydrazine and hydrogen co-injection (HHC), [7][8][9] which is done as hydrazine injection into reactor water with a small amount of hydrogen though the FW system, in order to mitigate a crack growth rate (CGR) by reducing bulk reactor water concentrations of oxidants. Required fundamental characteristics of the HHC are as follows:…”

Hydrazine and Hydrogen Co-injection to Mitigate Stress Corrosion Cracking of Structural Materials in Boiling Water Reactors, (III) Effects of Adding Hydrazine on Zircaloy-2 Corrosion

“…1) Since hydrazine is a reducing agent, it is expected to reduce the oxidizing agents in the coolant. [2][3][4] Hydrazine reacts with oxygen to produce water and nitrogen in the downcomer. Some hydrazine decomposes thermally into ammonia and nitrogen at temperatures higher than 443 K. 3,5) Although these decomposition products will be present in the reactor core, the specific effects of nitrogen and ammonia on the corrosion of Zircaloy-2 in BWRs are unknown.…”