Plutonium and Radiocerium contents in shallow sea sediment collected at off shore Ibaraki Prefecture, Japan.

The contents of 239, 240Pu and 144Ce in shallow water sediment were measured by means of chemical separation and a spectrometry on 239, 240Pu and β counting on 144Pr. The samples were collected in 1977 and 1980 at of shore of Ibaraki Prefecture for comparison of pre-and after operation of Tokai spent fuel reprocessing plant.The ranges and mean values of 239, 240Pu and 144Ce contents determined in the samples are 0.02-2.85 Bq/kg-dry (0.55-77 pCi/kg-dry) with mean values of 0.93 Bq/kg-dry (25 pCi/kg-dry) in 1977 and 0.52 Bq/kg-dry (14 pCi/kg-dry) in 1980 for 239, 240Pu, and 0.67-19.5 Bq/kg-dry (18-526 pCi/kg-dry) with mean value of 5.44 Bq/kg-dry (147 pCi/kg-dry) in 1977 and 1.59 Bq/kg-dry (43 pCi/kg-dry) in 1980 for 144Ce, respectively. These values showed no environmental accumulation of the nuclides by the operation was detected. The contents of two nuclides showed strong correlation each other in the samples. The inventory of 239, 240Pu in the sediment was estimated to be 43.7 MBq/km2 (1.18 mCi/km2) from core samples analyses in 1977, which is almost the same with the reported value of cumulative fallout 239, 240Pu in Tokyo.