A unit of energy used in the nuclear power and nuclear weapons industries. One megawatt day equals exactly 24 megawatt hours, 86.4 gigajoules (GJ), about 81.89 million Btu, or about 63.7 billion foot pounds
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}