A flow injection type hydrogen peroxide detection system with a sub-ppb detection limit has been developed to determine hydrogen peroxide concentration in water sampled from a high temperature, high pressure hydrogen peroxide water loop. The hydrogen peroxide detector is based on luminol chemiluminescence spectroscopy. A small amount of sample water (20 ml) is mixed with a reagent mixture, an aqueous solution of luminol and Co 2þ catalyst, in a mixing cell which is installed just upstream from the detection cell. The optimum values for pH and the concentrations of luminol and Co 2þ ion have been determined to ensure a lower detectable limit and a higher reproducibility. The photocurrent detected by the detection system is expressed by a linear function of the hydrogen peroxide concentration in the region of lower concentration ([H 2 O 2 ]<10 ppb), while it is expressed by a quadratic function of [H 2 O 2 ] in the region of higher concentration ([H 2 O 2 ]>10 ppb). The luminous intensity of luminol chemiluminescence is the highest when pH of the reagent mixture is 11.0. Optimization of the major parameters gives the lowest detectable limit of 0.3 ppb.

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A high temperature high pressure water loop, which can control H 2 O 2 concentration with minimal oxygen (O 2) coexistence, has been fabricated. In order to evaluate the effects of hydrogen peroxide (H 2 O 2) on intergranular stress corrosion cracking. Not only static responses, i.e., electrochemical corrosion potential (ECP), of the stainless steel specimens exposed to H 2 O 2 and O 2 at elevated temperatures but also their dynamic responses, i.e., frequency dependent complex impedances (FDCI), were measured. The conclusions obtained by the experiments are as follows. (1) The ECP measured for the SUS 304 specimen exposed to 100 ppb H 2 O 2 reached the saturated level in 50 h, showed a larger value than the specimen exposed to 200 ppb O 2 and kept the same ECP level when the H 2 O 2 concentration was decreased to 10 ppb. (2) The FDCI measured for the specimen exposed to 100 ppb H 2 O 2 showed saturation in the low frequency semicircles; this behavior was determined by the electric resistance of the oxide film and caused by saturation of oxide film thickness. Behavior for the specimen exposed to 200 ppb O 2 was determined by the resistance of oxide dissolution, which was much larger than that for the specimen exposed to H 2 O 2. (3) The ECPs of the specimens exposed to 200 ppb O 2 after 200-h exposure to 100 ppb H 2 O 2 were higher than those exposed to only 200 ppb O 2 due to memory effects on oxide films. The specimens with pre-exposure to 200 ppb O 2 did not show these memory effects.

Corrosive conditions in BWRs are determined mainly by hydrogen peroxide (H 2 O 2). Then, a high temperature, high-pressure H 2 O 2 water loop was fabricated to identify the effects of H 2 O 2 on corrosion and stress corrosion cracking of stainless steel. By changing concentrations of H 2 O 2 and O 2 , in situ measurements of electrochemical corrosion potential (ECP) and frequency dependent complex impedance (FDCI) of test specimens were carried out and then characteristics of oxide film on the specimens were evaluated by analyzing FDCI data based on the equivalent circuit analysis. The following points were experimentally confirmed. (1) The ECP and FDCI data of the specimens exposed to 100 ppb H 2 O 2 were not affected by co-existing O 2 with the same level oxidant concentration and they were also not affected by pre-exposure to 200 ppb O 2. From the viewpoint of ECP, this meant that corrosive conditions of hydrogen water chemistry were the same as those of normal water chemistry. (2) The low frequency semicircles of the FDCI data for the specimens exposed to 100 ppb H 2 O 2 reached a saturation value which was much smaller than saturation values for specimens exposed to 200 ppb O 2 and to 10 ppb H 2 O 2. (3) Smaller oxide dissolution resistance and larger electric resistance of the oxide film were obtained for the specimens exposed to 100 ppb H 2 O 2. This caused ECP to increase by shifting the anodic polarization curve of stainless steel to the high potential side.

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