An apparatus was designed and constructed to test the performance of coatings under conditions of high-pressure steam and radiation that might exist under a loss-of-coolant accident (LOCA). Results from the “simultaneous” exposure of coatings to high-pressure steam and radiation are compared to results obtained from the conventional “simulated” test procedures. Coating systems were selected that had a history of performing well under simulated LOCA conditions and included zinc-based, epoxy, and phenolic primers with phenolic and modified phenolic topcoats. Coatings were exposed to 60Co radiation doses in the range of 108 to 109 rad. The study showed that the conventional simulated LOCA conditions were more severe on the coatings than those tested under the simultaneous exposure to high-pressure steam and 60Co radiation. It was concluded that coatings that satisfactorily passed the simulated LOCA tests will also pass the simultaneous LOCA tests.