Analysis of In-Reactor Stress Relaxation Using Irradiation Creep Models

Abstract

Irradiation creep and stress relaxation data are available from the United Kingdom for 20 percent cold-worked Type M316, 20 percent cold-worked Type FV548, and FHT Type PE-16 using pure torsion in the absence of swelling at 300 °C (572 °F). Irradiation creep models were used to calculate the relaxation and permanent deflection of the stress relaxation tests. Two relationships between irradiation creep and stress relaxation were assessed by comparing the measured and calculated stress relaxation and permanent deflection. The results show that for Types M316 and FV548 the stress relaxation and deflection may be calculated using irradiation creep models when the stress rate term arising from the irradiation creep model is set equal to zero. In the case of Type PE-16, the inability to calculate the stress relaxation and permanent deflection from the irradiation creep data was attributed to differences in creep behavior arising from lot-to-lot variations in alloying elements and impurity content. A modification of Types FV548 and PE-16 irradiation creep coefficients was necessary in order to calculate the stress relaxation and deflection. The modifications in Types FV548 and PE-16 irradiation creep properties reduces the large variation in the transient or incubation parameter predicted by irradiation creep tests for Types M316, FV548, and PE-16.