A subcooled nucleate boiling computer code (with 3D heat conduction in solid and 1D forced convection in fluid) that incorporates a good estimation of the single-phase and two-phase pressure drop was developed to evaluate a monoblock design of the divertor with smooth tubes as well as a wide variety of cooling designs. Using one of the monoblock divertor designs proposed by the European International Thermonuclear Experimental Reactor (ITER) team as of March 1995, it was found that under a normal steady state operating condition with a peak heat flux of about 5 MW/m2, the water flow remained in the single phase liquid regime. Under an abnormal operating condition with a peak heat flux of about 20 MW/m2, the partially developed boiling (PDB) regime occurred where the local critical heat flux safety factor, (SFCHF=CHF(z)/q“(0=0°)), was estimated to be about 1.4 using the Tong-75 CHF correlation. This indicates that further increases in the magnitude of the heat flux beyond 20 MW/m2 may raise safety concerns for the design. By increasing the mass flux, decreasing the inlet water temperature, or increasing the inlet water pressure, the CHF safety margin of the design can be increased without inserting twisted tapes inside cooling tubes.