Some thermal-hydraulics aspects of the impurity control system for FED/INTOR

This paper addresses two important aspects of thermal-hydraulics related to the design of limiter/divertor of Fusion Engineering Device and International Tokamak Reactor. The results of both analyses provide input to the determination of the lifetime of the limiter/divertor which is the most critical engineering problem for the impurity control system. The first part of the paper provides temperature calculations for the limiter and divertor. Steady-state, two-dimensional, temperature distributions are obtained, through the use of the computer code THTB, for the top surface of the limiter or divertor plate and for the leading edge (cylindrical geometry) of the limiter. Results are reported for various combinations of coating and structural materials. Thermal conductivity and coating thickness are found to be the most important parameters for given surface heat flux distributions. At the leading edge, there are two factors competing with each other when the coating material is relatively thick. The radial reduction in heat transfer area tends to increase the temperature while radiative heat transfer losses at high surface temperature tends to decrease the structural temperature. The second part of the paper describes the analysis of the tangential motion of a melt layer during plasma disruption. An analytical solution is developed. The results show that fairly large displacement (about 10 mm) could be reached under nominal conditions. Limitations of this analytical model are discussed and possible improvements are proposed