EVALUATION OF A MONOBLOCK DIVERTOR DESIGN FOR THE ITER TOKAMAK

A subcooled nucleate boiling computer code (with 3D heat conduction in solid and ID forced convection in fluid) that incorporates a good est imation of tile single-phase and two-phase pressure drop was developed to evaluate a monoblock design of the divertor with smooth tubes as w ell as a wide variety of cooling designs. Using one of the monoblock d ivertor designs proposed by the European International Thermonuclear E xperimental Reactor (ITER) team :Is of March 1995, it was found that u nder a normal steady state operating condition with a peal; heat flux of about 5 MW/m(2), the water flow remained in the single phase liquid regime. Under an abnormal operating condition with a peak heat flux o f about 20 MW/m(2), the partially developed boiling (PDB) regime occur red where the local critical heat flux safety factor, (SFCHF=CHF(z)/q ''((theta=0 degrees))), was estimated to be about 1.4 using the Tong-7 5 CHF correlation. This indicates that further increases in the magnit ude of the heat flus beyond 20 MW/m(2) may raise safety concerns for t he design. By increasing the mass flux, decreasing the inlet water tem perature, or increasing the inlet water pressure, the CHF safety margi n of the design can be increased without inserting twisted tapes insid e cooling tubes.