TRITIUM PERMEATION AND WALL LOADING IN THE TFTR VACUUM VESSEL

The problems of tritium permeation through and loading of the TFTR vacuum vessel wall structural components are considered for various TFTR operating scenarios and outgassing modes. A general analytical solution to the time-dependent diffusion equation which takes into account the boundary conditions arising from the tritium filling gas as well as the source function associated with implanted energetic charge exchange tritium is presented. Expressions are derived for two quantities of interest: (1) the total amount of tritium leaving the outer surface of a particular vessel component as a function of time, and (2) the amount retained as a function of time. These quantities are evaluated for specific TFTR cases. The results are that permeation through the vessel is important only for the bellows during discharge cleaning if the wall temperature rises above similar 150 degree C. At 250 degree C, after 72 hours of discharge cleaning similar 200 Ci would be lost. The wall loading is most severe in the stainless-steel plate sections during normal pulsed operation where similar 600 Ci would be retained after 1000 shots if the walls were at 20 degree C. Maintaining the temperature of the walls above 100 degree C greatly lessens the problem. The 600 Ci in the wall would be reduced to similar 10 Ci if the wall were heated to 250 degree C for about 60 h.