This paper is a study to reduce the excessive conservatism of the stress - based evaluation method which is the existing evaluation method. The first object was evaluated for the shut down cooling system of OPR1000, and the second object was evaluated for the hot leg of APR1400. In the shut down cooling system, the conservativeness is compared for the chaboche model and the bilinear kinematic hardening (BLKH) model. The Hot-leg gave each other a different acceleration history and compared the results. Applying stress based on stress based evaluation methods, stress based on stress assessment methods was also used to identify excessive conservatism.