Systems and methods for reducing or eliminating corrosion of components of a reactor system, including a supercritical water gasification system, are described. The reactor system may include a reactor vessel configured to receive a reactor fluid through a reactor fluid inlet and a product source fluid corrosive to portions of the reactor system through a product source fluid inlet. The product source fluid may react with the reactor fluid to produce one or more reaction products, such as a fuel gas. The product source fluid inlet may be arranged within the reactor fluid inlet such that the product source fluid entering the reactor vessel is encased by a fluid conduit formed by the flow of reactor fluid entering the reactor vessel. The layer may operate to reduce corrosion by forming a barrier between the product source fluid and the surface of the reactor fluid inlet and/or the reactor vessel.