Fission-fusion correlation of void swelling in pure nickel

Microstructures have been compared in annealed and cold worked pure nickel irradiated with fission (JOYO) and fusion (RTNS-II) neutrons. The swelling is found to be considerably higher for the fusion neutrons than for the fission neutrons on the dpa basis. This difference is due mainly to the void size. Since the void size is found to have a close relation with the damage production rate, it is expected that the present fission-fusion difference is caused mainly by the difference in damage production rate. The effects of cold work on swelling are found to be also a function of the damage production rate. The present study has shown the importance of the damage production rate in the correlation studies. Quantitative estimation of the effects of PKA spectral or transmutative differences for fission and fusion neutrons seems to be possible only after fission and fusion neutron irradiations with highly controlled damage production rate as a parameter are achieved.