Method for decontaminating metal surfaces of a nuclear facility

A method for decontaminating a metal surface exposed to radioactive liquid or gas during operation of a nuclear facility, wherein the metal surface is covered with a metal oxide layer including chromium and radioactive matter, the method comprising:

• a) an oxidation step wherein the metal oxide layer is contacted with an aqueous oxidation solution for converting chromium into a Cr(VI) compound and dissolving the Cr(VI) compound in the oxidation solution, wherein the aqueous oxidation solution comprises a permanganate oxidant but no additional mineral acid;
• b) a first cleaning step wherein the oxidation solution containing the Cr(VI) compound is passed directly over an anion exchange material and the Cr(VI) compound is immobilized on the anion exchange material;
• c) a decontamination step following the first cleaning step wherein the metal oxide layer subjected to the oxidation step is contacted with an aqueous solution of an organic acid for dissolving the metal oxide layer, thereby forming a decontamination solution containing the organic acid, metal ions and radioactive matter, and wherein the decontamination solution is passed over a cation exchange material for immobilizing the metal ions and radioactive matter;
• d) a second cleaning step wherein the organic acid contained in the decontamination solution is decomposed;
• and
• e) optionally repeating steps a) to d).