The answer depends, in part, on how long the reactor will be mothballed. For answers to these types of question, I refer to MTI Publication 34 - Guidelines for the Mothballing of Process Plants written by Ronald Twigg. For jacketed reactors, the general recommendation for reactors is to: 1) Drain all jackets and blow with dry air or nitrogen. 2) Fill the jacket with inhibited antifreeze to the strength required for expected ambient temperatures. Vessels inside heated buildings require no antifreeze and the jacket is left open after draining and drying. For more information and additional details, consider obtaining a copy of this MTI publication.