As US pressurized water reactor operators consider a potential change in water chemistry from a LiOH additive to a KOH additive, qualification testing has been conducted to demonstrate that the change will not adversely impact materials behavior. As part of a broader qualification program being led by the Electric Power Research Institute, irradiation-assisted crack growth rate testing has been conducted on neutron irradiated Type 304 stainless steel. An ‘on the fly’ water change testing technique allows the water chemistry to be changed during the crack growth rate test, comparing the effects of the different water environments on the same sample, and the same crack. A series of four such tests using round compact tension specimens identified no effect of the changing water chemistry on the crack growth rate. This helps to provide assurance that changing to a KOH water chemistry would not adversely affect the austenitic stainless steel reactor materials.