Abstract
In connection with the operation of the first spent fuel reprocessing plant in Japan, the monitoring of marine sediment off the coast of Tokai-mura is needed to detect the influence of radioactive effluent from the plant. However, some projects of point-sampling of marine sediment in this area have revealed a wide range of variation from place to place in the concentrations of fallout radionuclides distributed by nuclear weapons tests. Accordingly, a sampling design to detect any significant change by year of environmental levels of radionuclides in sediment should involve the sampling of sediment from a number of point in order to satisfy a given confidence level. A new method of line-sampling has been developed as a substitute for point-sampling at many points. The principle of this method comprised of resuspension of sediment by dragging a muddler on the bottom and collection of suspended sediment by a net type collector set up on a sledge. Operation of line-sampling by use of this apparatus and point-sampling by use of Smith-McIntyre grab sampler were made at two locations of different type and comparison of the analytical data for collected sediment was made. The sampling off Tokaimura (open sea, sandy sediment), where 137Cs was analyzed, showed a good coincidence between the two method, while the sampling in Urazoko-bay (silty sediment), where both 137Cs and 60Co were analyzed, showed a discrepancy suggesting a loss of fine silty sediment in the line-sampling method.
