Radioactive 58 Co and 65 Zn were used together to investigate the deposition behavior of cobalt and zinc in the oxide film formed on the stainless steel piping of an apparatus simulating the high temperature and pressure conditions of a boiling water reactor. Using these radioactive tracers allowed the experimental setup to closely approximate the conditions found in actual plants. The accumulation of 58 Co and 65 Zn on the stainless steel piping was monitored using an online gamma-ray detector. The results were as follows. At higher zinc concentrations, the early period of fast dep-osition was shortened, and the later deposition phase was slowed. Two mechanisms appeared to be responsible for the suppression of cobalt deposition by zinc injection. The first worked by decreasing the growth rate of the oxide film. This effect appeared most conspicuously in the outer oxide layer under normal water chemistry conditions. The second mechanism worked by reducing the cobalt concentration in the oxide film. This second effect was prominent in the inner oxide layer under hydrogen water chemistry conditions.

In order to understand corrosion behavior of stainless steel in BWR reactor water conditions, characteristics of oxide films on stainless steel specimens exposed to H 2 O 2 and O 2 in high temperature water were determined by multilateral surface analyses, i.e., SEM (scanning electron microscope), LRS (laser Raman spectroscope), SIMS (secondary ion mass spectroscope) and STEM-EDX (scanning transmission electron microscope). The following points were experimentally confirmed. (1) Oxide layers were divided into inner and outer layers: Outer layers of the specimen exposed to 100 ppb H 2 O 2 consisted of larger corundum type hematite (-Fe 2 O 3) particles, while inner layers consisted of very fine Ni rich magnetite (Fe 3 O 4). Outer layers of the specimen exposed to 200 ppb O 2 consisted of larger magnetite mixture particles, while inner layers consisted of fine Cr rich magnetite. (2) Outer oxide layers consisted of oxide particles. The oxide particles depositing on the specimens exposed to 100 ppb H 2 O 2 were divided into two groups, i.e., a larger particle group and a smaller particle group. For other specimens, the diameter distribution of depositing particles was a single peak. Particle density and size were changed by oxidant concentration. The average diameter of the particles (that of the smaller group only for the specimen expose to 100 ppb H 2 O 2) decreased with [O 2 ] and [H 2 O 2 ]. (3) Total oxide film thickness decreased with [H 2 O 2 ] and increased with [O 2 ]. (4) A larger dissolution rate at higher [H 2 O 2 ] resulted in a thinner oxide film with smaller particles and larger hem-atite particles.

Oxidation tests on Type 316 stainless steel were performed under hydrogen water chemistry and normal water chemistry for 500 hours with continuous injection of a 59 Co solution with and without 5 ppb of Zn injection. The present paper identifies the resultant oxides, analysed using analytical electron microscopy and complementary surface microstructural characterisation techniques. Zn injection has been shown to reduce Co incorporation in the inner oxide layer under both water chemistry conditions. The secondary effects of Zn injection on the oxide film growth have also been investigated and discussed.

No abstract

In order to understand corrosion behavior of stainless steel in BWR reactor water conditions, characteristics of oxide films on stainless steel specimens exposed to H 2 O 2 and O 2 in high temperature water were determined by multilateral surface analyses, i.e., SEM (scanning electron microscope), LRS (laser Raman spectroscope), SIMS (secondary ion mass spectroscope) and STEM-EDX (scanning transmission electron microscope). The following points were experimentally confirmed.(1) Oxide layers were divided into inner and outer layers: Outer layers of the specimen exposed to 100 ppb H 2 O 2 consisted of larger corundum type hematite (-Fe 2 O 3 ) particles, while inner layers consisted of very fine Ni rich magnetite (Fe 3 O 4 ). Outer layers of the specimen exposed to 200 ppb O 2 consisted of larger magnetite mixture particles, while inner layers consisted of fine Cr rich magnetite.(2) Outer oxide layers consisted of oxide particles. The oxide particles depositing on the specimens exposed to 100 ppb H 2 O 2 were divided into two groups, i.e., a larger particle group and a smaller particle group. For other specimens, the diameter distribution of depositing particles was a single peak. Particle density and size were changed by oxidant concentration.