Abstract The effects of surface nitridation of 316 SS on protection against arc erosion and on suppression of plasma cooling were investigated by using thermal shock loading of 75 J/cm 2. The volume loss by arcing was remarkably reduced by nitridation to about 1 6 . Meanwhile, the mass loss increased by nitridation to about 4 times as much as for the non-nitrided sample. It was understood by XMA analysis of the nitrided sample before and after arcing that the increased mass loss was mainly due to nitrogens released from the nitrided sample by arcing. The nitrided to non-nitrided ratio of the total radiated power of impurities released from the samples by arcing was roughly estimated to be about 0.47 despite the increase of the mass loss by nitridation.