AbstractA program was instituted to study and reproduce the in-reactor intergranular failures of Type-304 stainless steel fuel cladding found in superheated steam. The program was directed toward finding ways to eliminate the cause of failure or to use improved alloys that would be less susceptible to failure.A materials screening test was developed in the out-of-pile superheat facilities with 1.5 parts/106chloride added as sodium chloride to the recirculating water in the presence of typical boiling-water-reactor quantities of oxygen and hydrogen. During the test, the heater sheaths were exposed through several cycles to saturated steam (with its accompanying moisture carryover) and superheated steam. Failure of Type-304 stainless steel was obtained in periods of less than two weeks; the failures were predominantly transgranular. Type-347 and vacuum-melted Type-304 stainless steels failed in this NaCl-cycle test while Inconel-600, Incoloy-800, Hastelloy-X, Type-406 stainless steel, and vacuum-melted Type-310 stainless steel were acceptable.An improved chloride cycle test utilizing 0.5 parts/106chloride added as ferric chloride to the recirculating water was developed. An intergranular failure was obtained similar to that experienced in the superheat fuel cladding failures in the superheat in-pile loops in the Vallecitos Boiling Water Reactor. Sensitized Type-304 and Type-316 stainless steels failed intergranularly in this test. Inconel-600, Incoloy-800, and vacuum-melted Type-310 stainless steel did not fail when exposed to the test for much longer times.During the development and performance of the cycle runs, the superheat facilities were exposed to a myriad of conditions within the extremes of the test parameters involved. Intergranular chemical attack was experienced essentially independent of stress, but the attack was generally distributed. In the presence of high stress, the intergranular attack was more localized and advanced normal to the stress. This suggests that a definite interplay exists between chemical attack and stress, and that the application of the stress increases the rate of the intergranular attack preferentially in a direction perpendicular to the stress.