Effects of humidity on radiation resistance of electroless Ni plating

Electroless Ni plating is commonly used as a coating of machined parts because of its superior corrosion resistance. The ITER Blanket Remote Handling System will use electroless Ni plating but will be operated in a γ-ray radiation environment, for which corrosion resistance—essential for the remote maintenance of ITER in-vessel components—has never before been demonstrated. This paper presents irradiation tests of electroless Ni plating carried out under dry or humid conditions. Corrosion resistance of electroless Ni plating was markedly affected in humid environments, however, in dry environments radiation resistance was verified. From surface analyses we can infer that radiolysis-enhanced corrosion was most likely caused by hydroxyl radicals produced from the interaction of water vapor and γ-rays in humid environments.