A set of some approximate functions derived for the fast computation of the thermodynamic properties of heavy water at saturation, in subcooled liquid and superheated vapor states is presented. To derive these functions, the data given in the steam tables by Hill et al. AECL 7531 (1981) were accurately and successfully fitted with curves by using the least-squares method. Specific volume (or density), specific enthalpy, specific entropy, constant-pressure specific heat and temperature at saturation were approximated by a number of piecewise continuous functions of pressure whereas pressure at saturation was approximated by a piecewise continuous function of temperature for heavy water. Density in subcooled liquid state, specific volume in superheated vapor state, specific enthalpy, specific entropy and constant-pressure specific heat in both of these states were also approximated as piecewise continuous functions of pressure and temperature for heavy water. The correlations presented in this study can be used in the two-phase thermohydraulic system analysis of CANDU-PHW reactor with confidence. (C) 1997 Elsevier Science S.A.