This PhD thesis proposal is dedicated to the study of the effect of PWR primary circuit environment on fatigue life of components made of nickel based alloy 690. First, fatigue mean curve of this alloy will be experimentally evaluated in air since this environment is usually employed to determine fatigue mean curve in nuclear codes (in France, RCC-M). Then, and in order to evaluate fatigue life in a perfectly neutral environment, fatigue tests will be performed in vacuum. And, at last, in PWR primary environment. These tests will enable to determine if the RCC-M assomptions are correct for Ni based alloys but additionnal tests will be necessary to comprehend the effect of the environment. This study will be based on fractographic observation with striation measurements of the specimens employed for the reference curves described previously but also combining different successive environment on the same specimen and observing the evolution of crack initiation and propagation sites. The effect of the environment on plasticity at crack tip (and hence its propagation) will also be evaluated by TEM observations. These elements will enable to have a better comprehension on the effect of the environment on fatigue life of 690 Ni based alloy.​