Decommissioning plant canisters owing to its excellent corrosion resistant,

Decommissioning of the nuclear reactors involves
dismantling of the reactor components and removal of spent fuel to the
repository site. Owing to the lack of storage facility at the geological
repository, the usage of the dry storage canister near the seashore platforms for
storing spent fuel has been considered as an
appropriate option. Dry storage canisters are used to hold and maintain the
spent nuclear fuel for an interim period of 1 to 10 years before reprocessing
or final deposition in a geological repository.  Austenitic stainless steel are widely used as
the structural materials for nuclear power plant canisters owing to its
excellent corrosion resistant, fabricability and mechanical properties. However
these canisters were placed near the seashore platforms which makes the stainless
steel more prone to chloride contamination from salt deposition in highly humid
environment that could induce localised stress corrosion cracking (SCC) (where do you get stress from?) near the welded regions
leading to the degradation of structural integrity and leakage of irradiated
spent fuel into the environment, which would be a major concern 3. The extent
of the corrosion will adversely affect the structural integrity of the canisters,
therefore requiring adequate corrosion protection for stainless steel.

Over the recent years, Photocathodic
protection of stainless steel by metal oxide semiconductor coatings such as TiO2 4, ZnO2
5, ZrO2 6 have drawn a considerable interest among the
researchers. Among them, TiO2 coatings are more convenient due to
its inherent advantages such as high surface area, superior optolectrical
properties and long-term stability against corrosion 7. Under
excitation with the simulated ultraviolet radiation, TiO2 coatings can
generate the electron and hole pairs from the space charge layer. The generated
photoelectrons transfers to the metal surface, making its electrochemical
potential more negative than its corrosion potential, whereas the holes move
towards the electrolyte leading to the oxidation of H2O. Thus, TiO2
coating act as a non-sacrificial anode for the photocathodic protection of stainless
steels. The application of TiO2 on the surface of stainless steel is
more promising because of its simplicity, material and equipment cost. Several techniques such as sol-gel coating, chemical vapour
deposition, sputtering, spray pyrolysis, anodization and plasma spraying for
TiO2 deposition are in use. Solgel method offers many advantages in
terms of coating homogeneity, well-controlled TiO2 phase structure, and
good adherence over larger area.

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Many efforts have been made for the application
of TiO2 coating over the stainless steel substrate 8,9. However,
due to wide band gap energy and recombination of electrons and holes pairs absence of UV illumination disrupt the practical
application TiO2 coating. We intend to prevent these limitations of
plain TiO2 coatings by incorporating transition metal element Fe to
enhance the photocatalytic activity as well as the corrosion protection under
dark condition. The present study involves the preparation of multi-layered TiO2
thin film coating via solgel-derived dip coating process followed by annealing
treatment at various temperatures for different time duration. The
multi-layered TiO2 coating deposited over the 304SS substrate consists
of tri-layered amorphous-TiO2 /anatase-TiO2/Fe-TiO2
deposited on bare 304SS. It is proposed that Fe-doped
TiO2 layer will act as a charge storage layer to trap the electrons
during the UV illumination, whereas the anatase-TiO2 will be used to
generate the electrons to make the electrode potential shift to more negative
values. Further, the amorphous-TiO2 layer will acts as barrier to
prevent the stored electron from escaping the Fe-TiO2 layer once the
UV illumination is switched off.  The
same coating procedure was also previously studied on the indium-doped tin oxideG1  (ITO) in
order to study the influence of diffused elements on the photocathodic
protection for comparative studies.

Though our initial studies over the development of the
multilayer coatings provides the mitigation of the 304SS corrosion by reducing
the electrode potential to more negative values, still the potential raised
immediately towards its rest potential in the absence of UV illumination. G2 Moreover, a relatively higher
temperature annealing treatment was required by these techniques for the
conversion to crystalline anatase phase, which also led to the diffusion of
certain cations (Fe3+) from the 304SS substrate into the TiO2
coatings, therefore deterring its photocatalytic properties 8. Then we
investigated the influence of each TiO2 layer over the
photocatalytic activity separately, in which the as-prepared plain amorphous TiO2
coated 304SS showed slow decline of photo-voltage after cutting-off the UV
illumination, therefore protecting the material even after the shutdown of
UV-illumination. This phenomenon occurs mainly due to the diffusion of elements
such as Fe from the substrate metal during the annealing process. We also extensively
investigated the extent of corrosion current density of the coated specimen throughout
the UV illumination procedure over a period of 10hrsG3 . The
influence of various parameters such as temperature and thickness of the
coating was studied.

The surface morphologies of the samples were studied by
scanning electron microscopy (SEM), Energy
dispersive X-ray spectroscopy (EDX), and laser raman G4 spectroscopy.
The crystalline nature of the TiO2 was evaluated by the x-ray
diffraction (XRD) The Auger depth profile analysis was made to quantify the
amount of Fe diffused from the substrate material. In addition, the
photocatalytic responses of these coatings exposed to various acidic and
alkaline aqueous solutions under aerated and deaerated conditions was also
studied.

 

 G1No capital

 G2Why writing this in introduction (if its from your study)? If its
others study, then can be added in introduction

 G3Should be written as 10 h.

 G4R should be in capital (Raman)