Section I11 of the ASME Boiler and Pressure Vessel Code specifies fatigue design curves for structural materials. These curves were based on tests of smooth polished specimens at room temperature in air. The effects of reactor coolant environments are not explicitly addressed by the Code design curves, but recent test data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of carbon and low-alloy steels. Under certain loading and environmental conditions, fatigue lives of test specimens may be a factor of =70 shorter than in air. Results of fatigue tests that examine the influence of reactor environment on crack initiation and crack growth of carbon and low-alloy steels are presented. Crack lengths as a function of fatigue cycles were determined in air by a surface replication technique, and in water by block loading that leaves marks on the fracture surface. Decreases in fatigue life of low-alloy steels in high-dissolved-oxygen (DO) water are primarily caused by the effects of environment during early stages of fatigue damage, i.e., growth of short cracks lo0 pm, crack growth rates in high-DO water are higher than in air by one order of magnitude. The effects of LWR environments on growth of short cracks are discussed.

Corrosion tests have been conducted to determine the compatibility of gallium with candidate structural materials for the International Thermonuclear Experimental Reactor (ITER) first wallhlanket systems, e.g., Type 316 stainless steel (SS),Inconel 625, and Nb-5 Mo-1 Zr. The results indicate that Type 316 S S is least resistant to corrosion in static gallium and Nb-5 Mo-1 Zr alloy is most resistant. At 40O0C, corrosion rates for Type 316 SS, Inconel 625, and Nb-5 Mo-1 Zr alloy are ~4 . 0 , 0.5, and 0.03 mmlyr, respectively. Iron, nickel, and chromium react rapidly with gallium. Iron shows greater corrosion than nickel at 400°C (288 and 18 mmlyr, respectively). The present study indicates that at temperatures up to 400°C. corrosion occurs primarily by dissolution and is accompanied by formation of metal/gallium intermetallic compounds. The growth of intermetallic compounds may control the overall rate of corrosion.

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