Critical heat flux is one the important design parameters for nuclear reactor especially for boiling water reactors. It limits power and various operating conditions of a reactor like pressure, flow etc. It is more important for natural circulation boiling water reactor due to its various characteristics. It is necessary to keep margin for CHF in term of Minimum Critical Heat Flux Ratio (MCHFR). Optimisation of such margin improves economic of a reactor. Correlations of critical heat flux are continually being revised as a result of additional experimental data, changes in fuel assembly design, and improved calculation techniques involving coolant mixing and the effect of axial power distributions. There are large variations in different correlation for evaluation of critical heat flux and large numbers of uncertainities are involved. This results in further reduction in margins available. In this paper critical heat flux in a coolant channel of Advanced Heavy Water Reactor is estimated using different correlation at various axial locations. Optimisation study is done by minimizing Minimum Critical Heat Flux Ratio (MCHFR) by use of different axial power profiles. Various parametric studies are done for different number of nodes, different power ratings, thermal hydraulic conditions, different correlations etc.

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