Recent trends in coping with embrittlement problems in reactor pressure vessels (RPVs) show two main directions of development: (1) improvement of the vessel materials and (2) limitations of fluence over the design life of the RPV. For several reasons, however, adequate irradiation surveillance programs are still considered to be necessary in the future, despite possible improvements resulting from such research activities.

Since the introduction of linear elastic fracture mechanics (LEFM) and elastic-plastic fracture mechanics, (EPFM), irradiation surveillance programs show a trend towards direct measurement of fracture toughness, in addition to relying on the conventional nil-ductility transition temperature (NDTT) shift as a relative measure of embrittlement. Some basic considerations concerning the selection of specimen types for irradiation surveillance programs and some technical aspects of currently used specimen types are discussed.