[en] This report presents a set of simplified models for assessment of human exposures resulting from potential underground releases of C-14. These models were used in the SFR1 SAR08 and KBS-3H safety assessments. The proposed models can be used to assess continuous, as well as pulse-like C-14 releases, to various types of biosphere objects: forest ecosystems, agricultural lands, sea basins and lakes. It is also possible to make assessments of exposures resulting from the use of contaminated fresh waters, for example from an impacted well, for irrigation of vegetables. Models are also proposed for scenarios where lakes and sea basins are transformed into terrestrial objects due to land rise, filling of lakes and other natural or human induced processes. The exposure pathways considered in dose calculations with the models are: ingestion of contaminated food and water for both terrestrial and aquatic ecosystems, inhalation of contaminated air for terrestrial ecosystems. The exposure by external irradiation is not considered, as C-14 is a pure low energy beta emitter. The report provides an overview of the behaviour of C-14 in the environment, including an outline of the conceptual assumptions implicit in the proposed models. The proposed models are based on the so-called specific activity approach, which has been recommended by the UNSCEAR and the IAEA for assessment of doses resulting from C-14 releases to the environment from nuclear installations. The equations for estimation of the C-14 specific activities in environmental compartments have been derived from a combination of several realistic and conservative assumptions, which are documented and justified in the report. The models can be used in safety assessments of geological repositories of radioactive waste, to carry out cautious, but still not over conservative dose estimations, which can be compared with regulatory dose constrains. Comparative studies with the models indicate that the worse case situations will be associated with releases to small lakes, especially if these have a low productivity and relatively long water residence times. Releases to terrestrial ecosystems and sea basins will generally result in lower annual doses per unit release rate, as in these systems the residence time in air and water, respectively, of the released C-14 are very short compared with the characteristic times of assimilation of carbon by primary producers. The study also indicates that accumulation of C-14 in lake and sediments and subsequent exposure to terrestrial systems formed on these sediments does not result in substantial annual doses per unit release rate, as compare with those received from releases to the corresponding aquatic ecosystem. In all cases considered in the study, the annual doses per unit release rate via food ingestion were much higher than the annual doses by other pathways, like inhalation and water ingestion, which is consistent with results reported from other studies. The uncertainty analysis shows that in most cases the dose predictions are within a factor from 5 to 20. This is a smaller range of uncertainty than the ranges that are obtained in assessments using transfer factors, which show a variability of several orders of magnitude. The results of the sensitivity analysis indicate that a few easily measured parameters have a dominant effect on the dose predictions: the wind speed, the concentration in water of dissolved inorganic (orig.)