To effectively reduce the radioactivity concentration in reactor water. In an embodiment, a method of repairing a fuel assembly in a nuclear reactor, comprising: applying a compound containing at least one substance selected from the group consisting of TiO.sub.2, TiCl.sub.4, Ti(OH).sub.4, TiF.sub.4, TiCl.sub.3, TiN, TiC, Ti(SO.sub.4).sub.2, Ti.sub.3O.sub.5, Ti(NO.sub.3).sub.4, Al.sub.3O.sub.3, Al(OH).sub.3, AlCl.sub.3, Al(NO.sub.3).sub.3, Al.sub.2(SO.sub.4).sub.3, WO.sub.2, WO.sub.3, WC.sub.16, WF.sub.6, (NH.sub.4).sub.10W.sub.12O.sub.41.5H.sub.2O, H.sub.2WO.sub.4 and H.sub.4WO.sub.5 to a surface of a fuel rod of the fuel assembly.

A chemical decontamination reagent containing a reducing agent, a reductive metal ion, and an inorganic acid is provided to remove a radioactive oxide layer on a metal surface. The reagent can dissolve the radioactive oxide layer on the metal surface effectively at a relatively low temperature and enables a simple process of contacting the reagent to the radioactive oxide, thus economically effective in terms of cost and time required for the process. Since the decontamination does not use a conventional organic chelating agent such as oxalic acid, but the reducing agent as a main substance, the residuals of the reducing agent remained after decontamination can be decomposed and removed with an oxidizing agent. Due to the easy decomposition with the chemical decontamination reagent, secondary wastes can be minimized and the radionuclides remained in the decontamination reagent solution can be removed effectively.

A method for decontaminating the nickel-based alloy includes oxidization of an oxide film accumulating radioactive nuclides with a first oxidizing agent to elute nickel into a solvent and thus to transform into a low-nickel film (S13 to S15). Elution amounts of Nickel, Chromium, and iron in the solvent are measured in the step S15 of the first oxidation step. Based on the elution amount, a second oxidizing agent is selected in the step S16. With the second oxidizing agent, the low-nickel film is oxidized to elute Chromium and thus to transform into an iron-concentrated film (S17 to S19). The iron-concentrated film is reduced with a reducing agent after the second oxidizing step including the steps of S13 to S19 to be dissolved and thus to be removed (S22).

Disclosed a method for decontaminating a surface of a substrate or a method for decontaminating a gaseous medium using an inorganic ferromagnetic gel consisting of a colloidal solution comprising an inorganic thickening agent, a ferromagnetic compound and a solvent.

The invention relates to methods for mitigating the recontamination of carbon steel surfaces in a nuclear reactor or related water-containing systems and components, which have undergone a decontamination process. The methods include conducting a passivation process of the carbon steel surfaces directly following completion of the decontamination process, prior to the system or component being returned to service. In certain embodiments, a chelating agent is used in the decontamination process and is retained following completion of the process, for use in the subsequent passivation process. The passivation process forms a passivation film that is effective to reduce recontamination of the decontaminated carbon steel surfaces.

The invention relates to a method for dissolving an oxide layer containing chromium, iron, nickel, and radionuclides by means of an aqueous oxidative decontamination solution, which contains permanganic acid and a mineral acid and which flows in a circuit (K1), wherein the oxidative decontamination solution is set to a pH value 2.5.

The invention relates to a method for reducing the radioactive contamination of the surface of a component used in a nuclear reactor, which component is in contact with radioactively contaminated water, in which method a hydrophobic film is produced on the surface of a component by virtue of the surface being wetted with an aqueous solution which contains a film-forming amphiphilic substance.

The present invention provides a decontamination method including the steps of decontaminating an object containing radioactive contaminated metals or alloys with a chemical decontamination agent comprising sulfuric acid (H.sub.2SO.sub.4) and forming a Ba or Sr precipitate by adding Ba or Sr cation and hydroxyl ion or halogen anion salts to the decontamination waste water.

The present invention also provides a kit for decontamination including a chemical decontamination agent including sulfuric acid (H.sub.2SO.sub.4) to decontaminate an object containing radioactive contaminated metals or alloys and Ba or Sr cation and hydroxyl ion or halogen anion salts to be added to the decontamination waste water to form a precipitate.

The present invention concerns a method and device for oxidative erosion or for decontamination of a metallic surface, comprising a step consisting of intermittently polarizing the metallic surface to be eroded or decontaminated, placed in contact with a solution containing manganese VII, at a more anodic electric potential than the corrosion potential of said surface.

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.