Effectiveness of Tritium Removal from a CTR Lithium Blanket by Cold Trapping Secondary Liquid Metals Na, K, and NaK

Thermodynamic calculations were made on the distribution of hydrogen and tritium between various refractory metals and liquid lithium as a function of temperature. The limiting tritium pressures that can be attained by cold trapping secondary liquid metals such as sodium, potassium, and sodium—78 wt% potassium (NaK) were also calculated. In the absence of tritium breeding, these pressures are 2.5 × 10⁻⁵, 2 × 10⁻⁷, and 1.2 × 10⁻¹⁰ Torr for sodium, potassium, and NaK, respectively, which correspond to tritium concentrations in lithium of 45, 4, and < 1 ppm, respectively, at 700°C. For a 1000-MW(th) thermonuclear reactor with a tritium breeding rate of 150 g/day, a tritium recovery system that incorporates (a) a separate lithium purification loop with niobium as the permeable membrane, (b) NaK as the secondary heat transport fluid, and (c) tungsten cladding on the IHX tubes will yield a tritium pressure of 10⁻⁹ Torr or less in the secondary system. This configuration will result in a tritium release rate ∼10⁻⁶ g/h to the steam system for a tungsten-clad steam generator operating at ∼600°C. The corresponding activity release rate is ∼300 Ci/yr.