Surfactant effect on CHF (critical heat flux) was determined during water flow boiling at atmospheric pressure in closed loop filled with solution of tri-sodium phosphate (TSP, Na3PO4 center dot 12H(2)O). TSP was added to the containment sump water to adjust pH level during accident in nuclear power plants. CHF was measured for four different water surfactant Solutions in vertical tubes, at different mass fluxes (100-500 kg/m(2) s) and two inlet subcooling temperatures (50 degrees C and 75 degrees C). Surfactant solutions (0.05-0.2%) at low mass flux (similar to 100 kg/m(2) s) showed the best CHF enhancement. CHF was decreased at high mass flux (500 kg/m(2) s) compared to the reference plain water data. Maximum increase in CHF was about 48%A its compared to the reference data. Surfactant caused a decrease in contact angle associated with an increase of CH F from surfactant addition. (C) 2007 Elsevier Ltd. All rights reserved.