THE DISTRIBUTION OF CS-137 IN SEDIMENTS OF THE LITTORAL-ZONE OF A FORMER REACTOR COOLING POND

Previous studies in Pond B, a 12-m deep, 82-ha reservoir that once ser ved as a reactor cooling pond, had (i) suggested the preferential accu mulation of Cs-137 in sediments at a water depth of 3m within the litt oral zone and (ii) attributed this accumulation to the effects of eith er macrophyte vegetation or sediment slope. To test for the preferenti al accumulation of Cs-137 at intermediate depths within the littoral z one, sediment cores were taken at water depths of 0.5, 1, 2, 3, 4 and 5m along 6 transects in Pond B. The sediment structure was similar at all water depths in the littoral zone with a surface layer of 0.02-0.0 4 m of plant debris and fine sediments over a base of sandy sediments. The Cs-137 was largely restricted to the surface layer of fine sedime nts, and there was no indication of preferential accumulation of fine sediments or Cs-137 at water. depths of 3m. There was no apparent rela tionship between sediment slope and Cs-137 content. Although the Cs-13 7 entered Pond B more than 20 years ago, its prevalence in the surface layers of littoral zone sediments resembles the pattern observed for Cs-134 deposited in European lakes from the recent Chernobyl accident.