Abstract
This paper describes tests conducted on samples of Type 304 tubing from which fuel cladding in the replacement core for the Nuclear Ship Savannah was manufactured. The major objective of the tests was to determine if exposed nonmetallic inclusions in the tubing would have a detrimental effect on the corrosion resistance of the material in the N.S. Savannah's pressurized water reactor environment. Inclusions were located by ultrasonic techniques and were exposed by metallographic methods. Two general types of inclusions were present: (1) stringers, consisting of complex Mn-Fe-Cr oxides ranging in length from 0.005 to 0.050 inch, and (2) blocks, consisting of complex Mn-Fe-Cr silicates with a maximum length of 0.010 inch. Inclusion thickness varied from less than 0.001 inch for stringers to about 0.002 inch for the block type; maximum width of both types was approximately 0.004 inch. Tests were conducted in a 5 gallon autoclave made of Type 316 stainless steel. Test solutions consisted of deoxygenated, deionized water which met N.S. Savannah primary coolant water specifications. Water temperature was maintained at 332 C (630 F) which was the cladding surface temperature during reactor operation. System pressure was maintained above the saturation pressure of water at 332 C by applying an overpressure with a mixture of argon and hydrogen; nominal working pressure throughout the tests was 2,000 psig. Specimens containing exposed inclusions were evaluated metallographically after one, two, and three months of exposure; both solution annealed and furnace sensitized material were tested. No accelerated or preferential corrosion of the metal surrounding the inclusions or dissolution of the inclusions occurred. The only corrosion detectable was a light, general etching of the surface resulting in the formation of an adherent film of magnetite. There was no observable difference in corrosion resistance of solution annealed and sensitized metal.
