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

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Abstract
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.