RADIOACTIVE CONTAMINATION OF THE BALTIC SEA IN THE REGION OF THE LENINGRAD NUCLEAR-POWER-PLANT IN 1971-1996

The content of Sr-90 and Cs-137 in the Kopor'e Bay in 1971-1985 was sh own to be consistent with the global contamination level; however, in 1975-1979 a somewhat increased content of 90Sr over this level was obs erved, which was probably due to the operation of the Leningrad Nuclea r Power Plant (LNPP). At the same time no increase was observed in the concentration of Cs-137 and the other gamma-emitting radionuclides. A s a result of Chernobyl accident in 1986, the Cs-137 content in the Ko por'e Bay increased by a factor of 60, which was accompanied by the ap pearance of Cs-134 and other gamma-emitters. In the subsequent time th e radioactive contamination of the Kopor'e Bay decreased primarily thr ough carrying away with the Neva river waters. Simultaneously, contami nated waters moved to the west and concentrated in the open part of th e Baltic Sea. In 1996 the contamination of the Kopor'e Bay with 137Cs was 36 Bq m(-3), which is 5 times higher than that in 1985; the contam ination with 134Cs below the detection level; and that with Sr-90, 20 Bq m(-3) which corresponds to the global level.