Study on New Water Chemistry Control for Stabilization of Oxide Films in Coolant Systems of Light Water Reactors

The present status of water chemistry in Japanese LWR was widely reviewed from literature and discussion with relevant experts。Then zinc injection and noble metal chemical addition were picked up as major subjects in this project.It was shown experimentally and analytically that zinc ion injected forms complex ferrites and chromites as a result of interaction with Fe and Cr ions，respectively，on the surfaces of stainless steel and fuel cladding and that cobalt accumulation in the inveride oxide layer(Chromites)on the surface of stainless steel and fuel cladding and that cobalt accumulation in the inveride oxide layer。Consequently being effective for reducing the cobalt accumulation.It was also shown experimentall…More y that Cr(VI)ion in aqueous phase oxidizes Zr on contacting with Zircaloy and is precipitated on its surface as amorphous Cr(III)oxides in the absence of zinc ion but as crystaline zinc chromite in the presenee of zinc ion.This Cr deposition is considered to be closely related with cobalt dissolution from the surface deposits of the fuel and was found to be remarkably suppressed by the pre-conditioning of the Zircaloy.Platinum injection is now expected to make hydrogen injection more effective in BWR，and the chemical behavior of a tetra-ammine complex of Pt(II)and hexa-hydroxo-complex of Pt(IV)was investated in aqueous solutions of a tetra-ammine complex of Pt(IV)Gamma irradiation readily reduces both of the Pt complexes to Pt metal in the presence of H I D 22个D 2 or alcohols，but not in the presence of O I D 22个D 2.The diameters and the catalytic property of the small particles of Pt metal formed were found to be largely affected by the condition of the particle preparation。This result shows that the effect of radiation is very important in the noble metal addition in real plants.Less：Less

The present status of water chemistry in Japanese LWR was widely reviewed from literature and discussion with relevant experts. Then zinc injection and noble metal chemical addition were picked up as major subjects in this project.It was shown experimentally and analytically that zinc ion injected forms complex ferrites and chromites as a result of interaction with Fe and Cr ions, respectively, on the surfaces of stainless steel and fuel cladding and that cobalt accumulation in the inner oxide layer (chromites) on the surface of stainless steel is suppressed effectively by zinc injection while it is not necessarily effective for the suppression of cobalt pick-up in the outer layer (ferrites).The experimental result showed that zinc injection forms very thin inner oxide layer of zinc chromite that is very stable thermodynamically and thus reduces remarkably the corrosion of stainless steel, consequently being effective for reducing the cobalt accumulation.It was also shown experimentall … More y that Cr(VI) ion in aqueous phase oxidizes Zr on contacting with Zircaloy and is precipitated on its surface as amorphous Cr(III) oxides in the absence of zinc ion but as crystaline zinc chromite in the presenee of zinc ion. This Cr deposition is considered to be closely related with cobalt dissolution from the surface deposits of the fuel and was found to be remarkably suppressed by the pre-conditioning of the Zircaloy.Platinum injection is now expected to make hydrogen injection more effective in BWR, and the chemical behavior of a tetra-ammine complex of Pt(II) and hexa-hydroxo-complex of Pt(IV) was investigated in aqueous solutions under gamma-irradiation.The Pt(II) complex is easily reduced and forms Pt metal in aqueous phase by heating to 120 〜 150 ℃ while the Pt(IV) complex is not reduced and consequently does not form Pt metal only by the heating. Gamma irradiation readily reduces both of the Pt complexes to Pt metal in the presence of HィイD22ィエD2 or alcohols, but not in the presence of OィイD22ィエD2. The diameters and the catalytic property of the small particles of Pt metal formed were found to be largely affected by the condition of the particle preparation. This result shows that the effect of radiation is very important in the noble metal addition in real plants. Less