Basic research on supercritical water oxidation was undertaken in the 1990s at Sandia National Laboratory's Combustion Research Facility (CRF), in Livermore, CA. Originally proposed as a hazardous waste destruction technology in response to the Kyoto protocol, multiple waste streams were studied by Steven F. Rice and Russ Hanush, and hydrothermal (supercritical water) flames were investigated by Richard R. Steeper and Jason D. Aiken. Among the waste streams studied were military dyes and pyrotechnics, methanol, and isopropyl alcohol. Hydrogen peroxide was used as an oxidizing agent, and Eric Croiset was tasked with detailed measurements of the decomposition of hydrogen peroxide at supercritical water conditions.
In mid-1992, Thomas G. McGuinness, PE invented what is now known as the "transpiring-wall SCWO reactor" (TWR) while seconded to Los Alamos National Laboratory on behalf of Summit Research Corporation. McGuinness subsequently received the first US patent for a TWR in early 1995. The TWR  was designed to mitigate problems of salt/solids deposition, corrosion and thermal limitations occurring in other SCWO reactor designs (eg. tubular & vat-type reactors) at the time. The upper part of the vertical reactor incorporates a permeable liner through which a clean fluid permeates to help prevent salts and other solids from accumulating at the inner surface of the liner. The liner also insulates the outer pressure containment vessel from high temperatures within the reaction zone. The liner can be manufactured from a variety of materials resistant to corrosion and high reaction temperatures. The bottom end of the TWR incorporates a "quench cooler" for cooling the reaction byproducts while neutralizing any components that might form acids during transition to subcritical temperature. Proof-of-concept and performance advantages of the TWR for a variety of feedstocks was demonstrated by Eckhard Dinjus and Johannes Abeln at Forschungszentrum Karlsruhe (FZK), via direct comparison between a TWR and an adjacent tubular reactor.
Major engineering challenges were associated with the deposition of salts and chemical corrosion in these supercritical water reactors. Anthony Lajeunesse led the team investigating these issues. To address these issues Lajeunesse designed a transpiring wall reactor which introduced a pressure differential through the walls of an inner sleeve filled with pores to continuously rinse the inner walls of the reactor with fresh water. Russ Hanush was charged with the construction and operation of the supercritical fluids reactor (SFR) used for these studies. Among its design intricacies were the Inconel 625 alloy necessary for operation at such extreme temperatures and pressures, and the design of the high-pressure, high-temperature optical cells used for photometric access to the reacting flows which incorporated 24 carat gold pressure seals and sapphire windows.