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

Self Cite

Water chemistry in a simulated crack (crack) has been studied to understand the mechanisms of stress corrosion cracking in a boiling water reactor environment. Electrochemical corrosion potential (ECP) in a crack made in an austenite type 304 stainless steel specimen was measured. The ECP distribution along the simulated crack was strongly affected by bulk water chemistry and bulk flow. When oxygen concentration was high in the bulk water, the potential difference between the crack tip and the outside of the crack (ÁE), which must be one motive force for crack growth, was about 0.3 V under a stagnant condition. When oxygen was removed from the bulk water, ECP inside and outside the crack became low and uniform and ÁE became small. The outside ECP was also lowered by depositing platinum on the steel specimen surface and adding stoichiometrically excess hydrogen to oxygen to lower ÁE. This was effective only when bulk water did not flow. Under the bulk water flow condition, water-borne oxygen caused an increase in ECP on the untreated surface inside the crack. This also caused a large ÁE. The ÁE effect was confirmed by crack growth rate measurements with a catalyst-treated specimen. Therefore, lowering the bulk oxidant concentration by such measures as hydrazine hydrogen coinjection, which is currently under development, is important for suppressing the crack growth.

Section: Crack Growth Under Flow Conditionmentioning

confidence: 99%

“…We are now developing hydrazine and hydrogen coinjection (HHC) [7][8][9][10] to mitigate CGR by reducing bulk reactor water concentrations of oxidants. Coinjection is done as hydrazine injection into reactor water with a small amount of hydrogen through the feedwater system.…”

Section: Introductionmentioning

confidence: 99%

Hydrazine and Hydrogen Coinjection to Mitigate Stress Corrosion Cracking of Structural Materials in Boiling Water Reactors (VII)—Effects of Bulk Water Chemistry on ECP Distribution inside a Crack

Wada

Ishida

Tachibana

et al. 2007

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“…Corrosive conditions of BWR fuel cladding have been studied based on water radiolysis models, while its effects on corrosion behaviors were studies based on accelerated corrosion experiments [29,30]. …”

Section: Fuel Integritymentioning

confidence: 99%

Water chemistry technology – one of the key technologies for safe and reliable nuclear power plant operation

Uchida

Katsumura

2013

Water chemistry control is one of the key technologies to establish safe and reliable operation of nuclear power plants. Continuous and collaborative efforts of plant manufacturers and plant operator utilities have been focused on optimal water chemistry control, for which, a trio of requirements for water chemistry should be simultaneously satisfied: (1) better reliability of reactor structures and fuel rods; (2) lower occupational exposure and (3) fewer radwaste sources. Various groups in academia have carried out basic research to support the technical bases of water chemistry in plants. The Research Committee on Water Chemistry of the Atomic Energy Society of Japan (AESJ), which has now been reorganized as the Division of Water Chemistry (DWC) of AESJ, has played important roles to promote improvements in water chemistry control, to share knowledge about and experiences with water chemistry control among plant operators and manufacturers and to establish common technological bases for plant water chemistry and then to transfer them to the next generation of plant workers engaged in water chemistry. Furthermore, the DWC has tried and succeeded arranging R&D proposals for further improvement in water chemistry control through roadmap planning. In the paper, major achievements in plant technologies and in basic research studies of water chemistry in Japan are reviewed. The contributions of the DWC to the longterm safe management of the damaged reactors at the Fukushima Daiichi Nuclear Power Plant until their decommissioning are introduced.

“…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:…”

Section: Introductionmentioning

confidence: 99%

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

Wada

Ishida

Tachibana

et al. 2007

Self Cite

A calculation model has been developed in order to evaluate effectiveness of hydrazine and hydrogen co-injection (HHC) into reactor water for mitigation of intergranular stress corrosion cracking of structural materials used in boiling water reactors (BWRs). The HHC uses the strong reducing power of hydrazine radical, which is produced in the downcomer region under irradiation by -rays and neutrons. Some reactions and their reaction rate constants were determined based on experiments which were carried out in aerated water, hydrogenated water, and deaerated water. The calculated results were in good agreement with experimental data by a factor of two. The model was applied to a BWR and it was found that the HHC cut oxygen and hydrogen peroxide amounts dissolved in reactor water more effectively than hydrogen water chemistry alone. Thus, the required amount of hydrogen for hydrazine injection was much lower than that for hydrogen water chemistry. Consequently, electrochemical corrosion potential of structural materials could be lowered below À0:1 V vs. SHE without any increase of MS line dose rate, which has been a limitation of the conventional hydrogen water chemistry. The HHC was predicted to decrease crack growth rate of structural materials by a factor of 10.