Creep behavior of the F82H steel under irradiation with 17 MeV protons at 300 °C

Although fusion blankets are exposed to severe irradiation, its rear side would stay at rather a modest condition. In this research, the irradiation-induced deformation of F82H IEA-heat steel at 300 °C was examined. A torsion creep apparatus with a strain resolution of ∼10−7 was used with 17 MeV protons (2 × 10−7 dpa/s). At the lowest stress of 30 MPa, deformation in the direction against applied stress was observed. This ‘negative creep’ was attributed to the increase in elastic modulus due to irradiation. Such an effect was compensated for each measurement based on the modulus data measured during irradiation. Stress exponent n of irradiation creep rates was 1.5, very close to that of creep strain at 5 dpa of pressurized tubes. The predicted stress relaxation was slower than that for 5% cold-worked Type 316L steel, resulting mainly from the difference in n, smaller and closer to unity in the latter.