Dr. William (Bill) T. Sha is insightful, inventive, and the epitome of professionalism in his technical work.

I have had extensive contacts with Bill Sha, first at Argonne National Laboratory, and later at the U.S. Nuclear Regulatory Commission's Office of Nuclear Regulatory Research. In the latter capacity, I was charged, following the accident at TMI-2, with developing and executing a plan of reactor safety research focused on severe accidents. A major problem facing us was that of knowing whether, when, and how a badly damaged nuclear reactor core could be cooled by natural convection. The obvious problem was that the coolant flow paths were not readily described analytically, even if we knew precisely what they were. We turned to Bill Sha for help with this problem. The response, in a refreshingly short time, was the COMMIX code.