Radiation damage effects in nuclear materials

The slowing down of high energy fission products, and hence damage production due to high energy heavy ions in nuclear fuels is the source of nuclear energy. For fusion energy, damage due to high energy neutrons is important. For waste materials, finally, α-decay is the predominant source of atomic damage. The present paper serves also as introduction to a workshop on radiation damage in these waste matrices. Damage production due to the above sources in nuclear materials is reviewed, damage effects on physical properties of interest for technological applications are summarized, and new results are given on damage ingrowth in nuclear fuels. Emphasis is placed on ceramics for waste solidification and on nuclear fuels, since waste glasses are treated in detail in subsequent papers of the workshop. For the case of waste ceramics, large volume increases, formation of amorphous phases (metamictization) due to ion implantation or α-decay are observed leading to increased leach rates. A positive feature of damage is a generally observed increase of fracture toughness in the damaged state. Damage effects in the tailormade ceramic SYNROC (synthetic rock) developed in Australia are also described based on the above sources (ion implantation and α-decay of an incorporated actinide of high specific activity, Cm-244) for damage production. In addition, first channeling/Rutherford backscattering results on damage in the U sublattices of UO2 and UN due to ion implantation with fission product ions are given, determining the number of displaced U atoms per incident ion, as well as the spontaneous and the thermal recovery of the defects produced. In conclusion, it is shown that a good understanding exists of radiation damage effects in nuclear materials, both for fuels and for waste matrices. Some remaining open questions are pointed out. (orig.)