The present disclosure relates to a workpiece cleaning device and a cleaning method. The workpiece cleaning device comprises: a frame (1); and a plurality of cleaning tanks disposed on the frame (1) side by side, comprising a molten salt cleaning tank (2) for cleaning a workpiece with molten salt, a first rinsing tank (5) for rinsing the workpiece cleaned with the molten salt, a de-rusting cleaning tank (6) for cleaning the workpiece rinsed in the first rinsing tank (5) with a de-rusting agent, a second rinsing tank (7) for rinsing the workpiece cleaned with the de-rusting agent, and an anti-rust cleaning tank (8) for cleaning the workpiece rinsed in the second rinsing tank (7) with anti-rust liquid, which are sequentially disposed from upstream to downstream in terms of procedure.

The present disclosure relates to a workpiece cleaning device and a cleaning method. The workpiece cleaning device comprises: a frame (1); and a plurality of cleaning tanks disposed on the frame (1) side by side, comprising a molten salt cleaning tank (2) for cleaning a workpiece with molten salt, a first rinsing tank (5) for rinsing the workpiece cleaned with the molten salt, a de-rusting cleaning tank (6) for cleaning the workpiece rinsed in the first rinsing tank (5) with a de-rusting agent, a second rinsing tank (7) for rinsing the workpiece cleaned with the de-rusting agent, and an anti-rust cleaning tank (8) for cleaning the workpiece rinsed in the second rinsing tank (7) with anti-rust liquid, which are sequentially disposed from upstream to downstream in terms of procedure.

Disclosed are an ionic liquid for pickling a stainless steel capable of rapidly removing oxide scale from the stainless steel at room temperature without using nitric acid or hydrofluoric acid and a method for pickling a stainless steel by using the same. The method for pickling a stainless steel according to an embodiment includes performing electrolytic pickling treatment by immersing a stainless steel in a pickling solution including an ionic liquid, wherein the ionic liquid comprises at least one of an imidazolium cation, a betainium cation, a sulfonium cation, a piperidinium cation, a phosphonium cation, an ammonium cation, a pyridium cation, a pyrrolidinium cation, and a morpholinium cation, as a cationic functional group, and at least one of a halide anion, a sulfonate anion, an alkylsulfate anion, a phosphinate anion, a salicylate anion, a nitrate anion, a tetrafluoroborate anion, a hexafluorophosphate anion, and a bistriflimide anion, as an anionic functional group.

A method of decontaminating metal surfaces in a cooling system of a nuclear reactor comprises: an oxidation step, comprising at least one acidic oxidation step and at least one alkaline oxidation step wherein metal oxides and radioisotopes on the metal surfaces are contacted with aqueous permanganate oxidant solutions; followed by a decontamination step wherein an aqueous solution comprising oxalic acid, formic acid, citric acid, tartaric acid, picolinic acid, gluconic acid glyoxylic acid or mixtures thereof is used to dissolve at least part of the metal oxides and radioisotopes; and a cleaning step wherein radioisotopes are immobilized on an ion exchange resin; wherein at least one treatment cycle includes a high temperature oxidation step, wherein the permanganate oxidant solution is kept at a temperature of at least 100 C.

A method of decontaminating metal surfaces in a cooling system of a nuclear reactor comprises: an oxidation step, comprising at least one acidic oxidation step and at least one alkaline oxidation step wherein metal oxides and radioisotopes on the metal surfaces are contacted with aqueous permanganate oxidant solutions; followed by a decontamination step wherein an aqueous solution comprising oxalic acid, formic acid, citric acid, tartaric acid, picolinic acid, gluconic acid glyoxylic acid or mixtures thereof is used to dissolve at least part of the metal oxides and radioisotopes; and a cleaning step wherein radioisotopes are immobilized on an ion exchange resin; wherein at least one treatment cycle includes a high temperature oxidation step, wherein the permanganate oxidant solution is kept at a temperature of at least 100 C.

One aspect of this ferritic stainless steel sheet contains, by mass %, C: 0.03% or less, N: 0.05% or less, Si: 1% or less, Mn: 1.2% or less, Cr: 14% or more and 28% or less, Nb: 8(C +N) or more and 0.8% or less, and Al: 0.1% or less, with a balance being Fe and inevitable impurities, in which a film satisfying Expression 1 is formed in a surface thereof. Expression 1 is d.sub.fCr.sub.f+5(Si.sub.f+3Al.sub.f)2.0. In Expression 1, d.sub.f represents a thickness (nm) of the film, Cr.sub.f represents a Cr cationic fraction in the film, Si.sub.f represents a Si cationic fraction in the film, and Al.sub.f represents an Al cationic fraction in the film.

A method of decontaminating metal surfaces in a cooling system of a nuclear reactor comprises conducting a plurality of treatment cycles, with each of the treatment cycles comprising: an oxidation step wherein metal oxides including radioisotopes on the metal surfaces are contacted with an aqueous solution of a permanganate oxidant; a decontamination step after the oxidation step wherein the metal oxides are contacted with an aqueous solution of an organic acid selected from the group consisting of oxalic acid, formic acid, citric acid, tartaric acid, picolinic acid, gluconic acid, glyoxylic acid and mixtures thereof so as to dissolve at least part of the metal oxides and the radioisotopes; and a cleaning step wherein at least the radioisotopes are immobilized on an ion exchange resin; wherein the oxidation step comprises at least one acidic oxidation step and at least one alkaline oxidation step carried out one after another in either the same or different treatment cycles; and wherein the plurality of treatment cycles comprises at least one treatment cycle including a high temperature oxidation step, wherein the permanganate oxidant solution is kept at a temperature of at least 100 C. and, wherein the at least one reactor coolant pump is used to circulate and heat the oxidation solution inside the primary loop, and the residual heat removal system is used to control the temperature of the oxidant solution during the high temperature oxidation step.

A method of decontaminating metal surfaces in a cooling system of a nuclear reactor comprises conducting a plurality of treatment cycles, with each of the treatment cycles comprising: an oxidation step wherein metal oxides including radioisotopes on the metal surfaces are contacted with an aqueous solution of a permanganate oxidant; a decontamination step after the oxidation step wherein the metal oxides are contacted with an aqueous solution of an organic acid selected from the group consisting of oxalic acid, formic acid, citric acid, tartaric acid, picolinic acid, gluconic acid, glyoxylic acid and mixtures thereof so as to dissolve at least part of the metal oxides and the radioisotopes; and a cleaning step wherein at least the radioisotopes are immobilized on an ion exchange resin; wherein the oxidation step comprises at least one acidic oxidation step and at least one alkaline oxidation step carried out one after another in either the same or different treatment cycles; and wherein the plurality of treatment cycles comprises at least one treatment cycle including a high temperature oxidation step, wherein the permanganate oxidant solution is kept at a temperature of at least 100 C. and, wherein the at least one reactor coolant pump is used to circulate and heat the oxidation solution inside the primary loop, and the residual heat removal system is used to control the temperature of the oxidant solution during the high temperature oxidation step.

A catalyzed highly alkaline cleaning composition for cleaning stainless steel and other surfaces, namely those treated in clean-in-place processes, is disclosed. The composition comprises gluconic acid or salt thereof (e.g. gluconate) to serve as a corrosion and stain inhibitor for the high alkalinity compositions. The composition retains the cleaning and corrosion prevention properties of conventional clean-in-place solutions while being less expensive to produce.