The natural convection heat transfer from the outer surface of horizontal heated calandria vessel (CV) of PHWR which is submerged in confined vault water is studied. For this, experiments were carried out in a scaled test setup. Experimental results were used to estimate the heat flux and heat transfer coefficient around CV. Further these experimental results are also used to develop two correlations. First one is the estimation of angular variation of local natural convection heat  transfer coefficient in terms of the modified Rayleigh number with angle from the bottom of the cylinder CV. Another one is for estimation of angular variation of local natural convection heat transfer coefficient once averaged heat transfer coefficient is known.