Radiation impact from 137Cs, 134Cs, 90Sr on marine biota was modeled for early period of a hypothetical accident with sunken nuclear submarine K-159 during its surfacing and transportation in the Barents Sea. Dynamics of radioactivity in seawaters was modeled, using analytical 2-dimensional model of radionuclide dispersion from an instantaneous point release in seawaters. Radioactive contamination of waters and bottom sediments with 137Cs, 134Cs, 90Sr was calculated for distances from 200 m to 30 km from the source. Estimated dose of acute exposure accumulated within the first 10 days, was close to 100 mGy for bottom fish at a distance 200 m from the source. The probability of lethal effects in fish at this dose was estimated to be below 1%. Chronic exposures from 137Cs, 134Cs, 90Sr at a distance 200 m from the source during the first year after the accident, were the following: fish - 9,7 mGy/day, mollusks - 11 mGy/day, marine plants – 6,3 mGy/day. These dose rates exceeded the reference level, ensuring safety of marine biota. Therefore, in the vicinity of the accident place, the radiation situation was not safe for bottom fish, mollusks and plants. At distances more than 500 m from the accident place, expected dose rates of chronic exposure to marine biota were below reference level. Doses to biota from a hypothetical accident in the Barents Sea were caused mainly by external exposure from contaminated sediments, also due to accumulation of long-lived radionuclides from sediments to bottom biota.