Development of line-sampling method for marine sediment

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 of Tokai-mura (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. (author)