Critical heat flux (CHF) is a condition at which the maximum heat flux can be extracted from the heating surface without damaging the heating element. Operating beyond this point may damage the heating element. CHF sets a limit for the power extraction from the nuclear reactor fuel bundle. The reactor must operate below the critical heat flux and should have a margin for operation. This margin is commonly known as the Minimum Critical Heat Flux Ratio (MCHFR) or Minimum Departure from Nucleate Boiling Ratio (MDNBR), which is the ratio between critical heat flux and operating heat flux. Knowledge of CHF or MDNBR is important for the thermal design of a reactor. There are mainly four methods available to evaluate the CHF for a nuclear reactor fuel bundle: empirical correlation, look-up table approach, mechanistic modelling, and experimental analysis. Experimental analysis is superior amongst others in terms of accurate prediction. An experimental test facility, called the DNB test facility, is being designed for the CHF data generation for the 37-fuel pin bundle of the Indian Pressurised Heavy Water Reactor (IPHWR). An electrically heated Fuel Rod Cluster Simulator (FRCS) will be used to simulate the nuclear fuel bundle. A brief discussion on the DNB test facility and the importance of CHF for a nuclear reactor is presented here.