Tritium inventories and tritium distribution have been determined in boron glass absorber rods discharged from a pressurized water reactor first-cycle core and in spent boron carbide (B4C) control rods from a boiling water reactor. The total tritium inventory in the boron glass absorber rods from the Stade nuclear reactor amounts to ∼8.0×1010 Bq (2.2 Ci) per rod. Of this, 99.6% was fixed in the boron glass itself and 0.4% in the Al2O3 pellets. The 4×10−3% fractions in the tube cladding and support pipe and the 1×10−1% fraction in the fill gas accounted for an insignificant part of the total tritium inventory of the rod. This experimentally determined tritium inventory was a factor of 5 larger than that suggested by the calculated estimate. The discrepancy between analyzed and calculated values can be explained by tritium formation from lithium impurities in the boron glass, where a 30-ppm lithium content would be adequate for this tritium inventory to be generated by the reaction 6Li(n, α)3H. Evaluation of the B4C control rods from the Lin-gen nuclear reactor after 3 yr of operation gave a 3.2×1010 Bq (0.85-Ci) tritium inventory per B4C rod, while the total tritium inventory for a control rod assembly containing 60 B4C rods was ∼1.9×1012 Bq (50 Ci). The tritium generated was essentially bound 100% in the B4C, since the hulls contained only 6×10−3% and the fill gas only 2×10−4%.