The engineering law currently used by EdF for the prediction of the drop in the tightening torques of CW316 baffle to former bolts with the irradiation dose was determined from irradiation creep kinetics obtained from the deformation under neutron flux of pressurized tubes. These experiments investigated maximum hoop stress up to 220 MPa. In the frame of a French collaborative project between CEA and EDF started in 2011, it was identified the interest to enlarge the range of initial stress to study irradiation induced relaxation behavior as well to better quantify the kinetics of relaxation in the initial relaxation regime.