Tensile properties of austenitic steel fuel claddings irradiated in FFTF as the MONJU type fuel assemblies (MFA-1 and MFA-2)

The effects of high fluence irradiation and swelling on the tensile properties of austenitic steel fuel claddings; PNC316 and 15Cr-20Ni steel, which were irradiated in the FFTF as the MONJU type fuel assemblies (MFA-1 and MFA-2), were investigated. Tension tests were carried out to understand the irradiation effect on the tensile properties of these highly irradiated claddings with significant swelling. The results obtained in this study are as follows; 1) The yield stresses and ultimate tensile strengths at each test temperatures of PNC316 cladding samples were almost same as that of the lower-fluence samples (previous data). It is considered that there was no obvious decrease in strengths with increasing fluence up to 2.1 x 1027 n/m2) The yield stresses and ultimate tensile strengths at each test temperatures of 15Cr-20Ni steel cladding samples showed similar behavior to that of PNC316 samples. There was no obvious difference in tensile properties between PNC316 and 15Cr-20Ni steel. 3) The uniform and total elongations of both materials samples decreased significantly at 400 and 450degC and total elongation tended to be close to uniform elongation. This suggested that there was considerable irradiation embrittlement under irradiation conditions of this study, although samples retained a certain ductility after irradiation. 4) There was no significant deterioration in tensile properties of PNC316 and 15Cr-20Ni steel claddings with considerable swelling about 10%. (author)