A portion of the Service Level (SL) I coating systems inside the AP1000®1 containment become submerged during a design basis loss-of-coolant accident (LOCA) as a result of containment flood-up. The Design Basis Accident (DBA) qualification of SL I coatings for the AP1000 did not initially include post-DBA submergence conditions.
Submergence testing was performed using a standard test (Reference 2). Test articles were carbon steel coupons coated with one of two coating SL I coating systems; an untopcoated inorganic zinc system (Carboline Carbozinc® 11 HSN2) and a system consisting of inorganic zinc and an epoxy (Carboline Carboguard® 890N3) topcoat. Half of the inorganic zinc samples tested were irradiated to a total accumulated dose of approximately 1×109 rads prior to submergence testing.
Autoclaves were used to simulate the post-LOCA environment inside of the AP1000 containment. The working fluid was a boric acid solution buffered with trisodium phosphate (TSP) to a pH of approximately 7.8. The pressure and fluid temperature inside of the autoclaves was regulated to begin at ambient conditions followed by a pressurization and heat up following pressure and temperature conditions calculated for a cold leg break LOCA for the AP1000 plant, plus an added 10% margin, and the slowly decrease over the 30 day test period to saturation temperature at about 20 psia, simulating a cool-down of the AP1000 plant. Coolant samples of the autoclave inventory were taken and evaluated for dissolved chemical species at specific time intervals during the test.
Following exposure to the submerged test environment, each coupon was visually inspected immediately following removal from the autoclaves and was inspected again several days after completion of the test cycle for signs of blistering, rusting, lifting, peeling, discoloration, softening, etching, wrinkling, cracking, swelling, dissolving, delamination, and changes in gloss relative to their observed pre-test condition.