The potential (reaction) energy and reaction rate of an accidental sodium−water reaction are investigated for fast breeder nuclear reactor safety. The potential energy is calculated using the molecular orbital method with accurate Gaussian Quadratures in the density functional scheme. The gaseous reaction rate analysis focuses on collision theory rather than transition state theory; the latter of which is more for solvents/solutions. The rate constant was derived using classical molecular dynamics (MDs) in two dimensions (2D) with the rigid sphere model. The MD calculation reveals analytic sequences suppressing error accumulations and time consumptions. The 2D result is converted to the 3D value via a corresponding cross section ratio with a form factor, reproducing the experimental value. The availability of microscopic results to macroscopic flow dynamics is appended; renormalizing the kinematic viscosity coefficient with scale-independent constants. An effective (pseudo-) MD for the heat transfer is also appended. © 2012 Wiley Periodicals, Inc.