Tritium Permeation through Fe-2¼Cr-1 Mo Steam Generator Material

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Abstract
The permeability of tritium through Fe-2¼Cr-1 Mo steel (Croloy) steam generator material has been measured for the surface-clean metal and for the metal oxidized in steam at 755 K (482°C). The temperature dependence of tritium permeability has been measured for the unoxidized metal between 673 and 773 K; the apparent activation energy for permeation in this temperature range was found to be 39.14 ± 0.32 kJ/mol (9350 ± 80 cal/mol). After steam oxidation at 755 K and 0.2 MPa (2 atm) for about one month, the tritium permeation rate decreased by a factor of ~150 relative to the clean metal. This reduction factor agrees very well with that measured for a sample of tubing used in Atomics International’s Modular Steam Generator experiments under typical liquid-metal fast breeder reactor steam generator conditions. These results may be used to calculate rates of tritium transport from the intermediate heat transport system sodium through the steam generator tubes and into the steam/water system. From this information, eventual release rates to the environment can be determined.