What Is a Cryogenic Reactor? Principles, Design & Applications Answering the core question: What is a cryogenic reactor, and how does it enable chemistry below minus 40 degree C? A cryogenic reactor is a vessel engineered for sub-ambient operation down to minus 196 degree C using liquid-nitrogen (LN2) or chilled brine or glycol jackets. Low-temperature service exploits the ductile-brittle transition: L-grade 304L or 316L steels (carbon below 0.03 percent) retain toughness