A six-compartment metabolic model for tritium accumulation by bivalves was developed and validated using two observed data sets supplied in an international IAEA program for validation of environmental models, EMRAS (Environmental Modeling for Radiation Safety, 2003-2007). The data observed were presented in scenarios for model prediction of temporal change of HTO and OBT concentrations in Barnes mussels (Elliptio complanata). In the Uptake Scenario, mussels were transplanted from a site with background tritium concentrations into a lake, which has historically received tritium inputs over time from upgradient waste management areas. Another data set was presented in the Depuration Scenario for model prediction of the temporal decrease in HTO and OBT concentrations in the mussels following transplantation from the lake into another lake with significantly lower tritium levels. The model simulation was able to reproduce the observation that the amount of hydrogen taken from sediment was very small compared with that taken from lake water.