Method for treating a metal part of a primary circuit of a water-cooled nuclear reactor

A method for treating, during an operating cycle, an internal surface of at least one metal part of a primary circuit of a water-cooled nuclear reactor, the metal part being made from a nickel-based or cobalt-based alloy selected from a steam generator tube, a pump or a fitting,

• the method comprising:
• estimating a quantity of nickel liable to be discharged into the primary circuit by all the metal parts of the primary circuit in contact with the water of the primary circuit, during an operating cycle of the reactor;
• calculating a quantity of magnetite necessary for fixing the whole of the quantity of nickel estimated;
• forming a treated water obtained by dissolving the quantity of magnetite calculated in the water of the primary circuit when the water has a temperature of between 80° C. and 180° C.;
• and
• putting said treated water in circulation in the primary circuit so as to form, on the internal surface of at least one metal part, a layer of a protective oxide able to fix all or part of the quantity of nickel estimated;
• diverting a portion of the treated water circulating in the primary circuit during the operating cycle into an auxiliary circuit comprising a purification device;
• purifying the portion of the treated water using the purification device;
• reinjecting into the primary circuit the purified treated water;
• and
• injecting, into said auxiliary circuit and downstream of the purification device, an aqueous iron solution, so as to compensate for a quantity of iron removed from the purified treated water by the purification device.