DEVELOPMENT OF THE ULTRA-MICROHARDNESS TECHNIQUE FOR POST IRRADIATIONEXAMINATION OF FUEL CLADDING TUBES

Hardness measurements are potentially valuable for a quantitative disc ussion of embrittlement in the inner portions of fuel cladding tubes. The size of the indentation, however, is not negligible compared to th e measuring region, even when a micro Vickers hardness tester is emplo yed. This limits the measuring technique, and very little has been stu died about degradation phenomena in the inner portion of the tubes. A hardness measurement system, equipped with a depth-sensing indentation instrument, and the necessary post irradiation examination technique for specimens with high radioactivity were successfully developed and the following observational were obtained from the system's applicatio n example. The diffusion coefficient of oxygen obtained from the hardn ess of an unirradiated zirconium lined cladding with simulated oxidati on in the fuel rod showed good agreement with literature data. The cal culated diffusion coefficient from hardness in the inner portion of ir radiated Zircaloy-2 fuel rods was almost the same value as that of uni rradiated zirconium, which implied that neither neutron irradiation no r fission fragment bombardment enhanced the oxygen diffusion in the in ner portion of cladding tube.