Analysis of tritium evolution in Al2O3-coated FeCrAl fuel rods for PWRs.

• A 2D numerical simulation model for tritium release from Al 2 O 3 -coated FeCrAl fuel rods was developed. • Sievert's law and the Soret effect equations were coded and studied in the model. • The low release rate indicates that the Al 2 O 3 coating prevents tritium release effectively. • Tritium concentration at the gap is much higher than the inner cladding for Al 2 O 3 -coated fuel rods. • Locally uncoated defects lead tritium flux to bypass Al 2 O 3 coating and be released outside the fuel rod. FeCrAl is one of the ATF cladding solutions due to its excellent oxidation resistance. In this work, a 2D numerical simulation method was developed to study tritium release from the nuclear fuel pellets to the fuel-cladding gap, tritium adsorption on the inner surface of the cladding, and permeation through Al 2 O 3 -coated FeCrAl cladding into the coolant. For Al 2 O 3 -coated fuel rods, based on Sievert's law, tritium concentration at the pellet-cladding gap is much higher than that at the inner cladding surface for most of the time under normal conditions, which slows down the tritium release rate from the fuel rods. With Al 2 O 3 coating, tritium release from the fuel rods remains rising throughout the lifetime. The release rate is calculated to be low at the end of the lifetime, indicating that the Al 2 O 3 coating prevents tritium release. As the coating thickness decreases, the flux of tritium release is found to be increased. Locally uncoated drawbacks lead tritium in the gap to be preferentially adsorbed by the inner surface of FeCrAl, then diffused in FeCrAl, and finally released outside the fuel rod. Still, more actual irradiation operations and test data are needed. [ABSTRACT FROM AUTHOR]