For the aging of fuel reprocessing facilities, constant load tensile tests with controlled potentials and electrochemical tests for zirconium were conducted in nitric acid and sodium nitrate solutions. Consequently, information was obtained regarding the effects of nitric acid and nitrate ion concentrations on the stress corrosion-cracking initiation and effects of nitric acid and plutonium concentrations in solutions, along with the liquid temperature on natural potential. Based on the test results, a map was drawn to summarize the effects of nitric acid concentration on the crack initiation potential. This map can be used to confirm the initiation of stress corrosion cracking by comparing it with the actual environmental conditions of fuel reprocessing facilities. Moreover, the test results indicated that not only nitric acid but also nitrate ion associated with nitrate must be considered for evaluating the possibility of stress corrosion cracking.