Investigation of Cobalt Deposition Behavior with Zinc Injection on Stainless Steel under BWR Conditions

In order to examine the anodic polarization characteristics of typical structural materials of boiling water reactors (BWRs), the anodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in deaerated high purity water at 553 K using the previously reported measurement method which was confirmed suitable for high temperature -high purity water. In order to specify which constituent element determines the dissolution characteristics of these materials, the anodic polarization curves of pure iron, pure nickel, and pure chromium were also surveyed. The anodic polarization curve of 316L SS was determined to have active, passive, and transpassive states which were the same as type 304 SS (304 SS) showed. But, Alloy 182 had different polarization characteristics especially near the corrosion potential as it had no active state. From comparison results of the polarization characteristics of these materials and their constituent elements, the corrosion characteristics of these materials were concluded to be mainly determined by the corrosion characteristics of chromium.

Section: L Ssmentioning

confidence: 99%

“…Hosokawa and Nagase [15] reported the fractions of Fe, Cr, Ni in the oxide film which was formed on the surface of 304 SS after 1000 h in 553 K high purity water. Their results indicated that the oxide film consisted of two layers.…”

Section: L Ssmentioning

confidence: 99%

Determining factors for anodic polarization curves of typical structural materials of boiling water reactors in high temperature – high purity water

Tachibana

Ishida

Wada

et al. 2012

“…5) The outer layer of oxide could be dissolved under a reductive condition and was separated by cathodic electrolysis into constituent compounds. The test specimen was electrolyzed in an electrolyte solution of 5 wt% H 2 SO 4 and 0.5 wt% hexamethylentetramine with 100 A/m 2 .…”

Section: Oxide Film and Base Metal Corrosionmentioning

confidence: 99%

“…Furthermore, the preoxidation film that forms under simulated BWR conditions consists of aggregates of submicrometer particles, and is not really a uniform film. 5) A fine ferrite film coating has already been applied to electric devices to reduce electrical noises. 6) Inorganic salts, for example, ferrous chloride, ferrous sulfate, and sodium nitrite, were used as the chemical agents for ferrite film formation in these devices.…”

Section: Introductionmentioning

confidence: 99%

Development of a Suppression Method for Deposition of Radioactive Cobalt after Chemical Decontamination: (I) Effect of the Ferrite Film Coating on Suppression of Cobalt Deposition

Hosokawa

Nagase

Fuse

2010

Self Cite

In the last decade, chemical decontamination at the beginning of periodical inspection has been applied to many Japanese BWR plants in order to reduce radiation exposure. However, following the chemical decontamination, a rapid dose rate increase can be seen in some plants after just a few operation cycles. Oxide film, which easily incorporates radioactivity, might be formed after the chemical decontamination.We developed a new way to reduce the recontamination after the chemical decontamination to maintain long-term continued decontamination effects without any chemical injections or chemical controls in reactor water during operation. In our approach, a fine ferrite film is formed by the Hitachi Ferrite Coat process after oxide films formed during the plant operation are removed by the chemical decontamination process. We select Fe(HCOO) 2 aqueous solution, H 2 O 2 , and N 2 H 4 as the treatment chemicals for fine ferrite film formation for suitable BWR plant application. Our laboratory experiment results confirm a 60 Co deposition reduction effect of 1/5 compared with that of nontreatment for up to 3,100 hours. The fine ferrite film that was formed on the specimen before the 60 Co deposition test remains as a film structure after the test. The corrosion amount of the specimen is suppressed to 1/4 through the effect of the fine ferrite film.

“…The oxide films incorporating the radioactive species grow on the surface of the components, and so become a radiation source [1]. Since cobalt-60 ( 60 Co) is the main radioactive nuclide associated with this radiation source, some research groups have been developing countermeasure technologies for the 60 Co buildup on the surface of the components and have been studying the mechanisms of 60 Co incorporation into the oxide films [2][3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Investigation of cobalt buildup behavior and suppression by zinc injection on stainless steel under HWC conditions using simultaneous continuous measurements of corrosion and cobalt buildup

Ohashi

Ito

Hosokawa

et al. 2014

Self Cite

In boiling water reactor (BWR) plants, cobalt-60 (60 Co) is the main source of radiation exposure, and it builds up on oxide films of structural materials. The 60 Co buildup is caused by its incorporation into the oxide films. In the BWR plants using hydrogen water chemistry (HWC) to mitigate the oxidative environment, Zn injection has been applied to reduce the 60 Co incorporation. In this work, we studied the incorporation mechanism of 60 Co into the oxide films on type 316 stainless steel and the suppression mechanism of 60 Co incorporation. In order to discriminate between coprecipitation and adsorption of 60 Co incorporation under HWC conditions, we measured the corrosion amount of the base metal and the 60 Co buildup amount, using simultaneous continuous measurements for 500 h. The 60 Co incorporation increased with time both with and without Zn injections. We found that the time dependencies of 60 Co incorporation with and without Zn have one and two regions, respectively. In the initial stage for both, 60 Co was incorporated mainly by coprecipitation. After 100 h without Zn, 60 Co was incorporated by both coprecipitation and adsorption. These results mean that Zn suppressed both coprecipitation and adsorption of 60 Co.