Distribution of plutonium and americium in Bikini Atoll lagoon.

Abstract

Important factors that govern the redistribution and transport of radionuclides in Bikini Atoll Lagoon are particulate size and physical-chemical state. In water samples from Bikini the particulate fraction was collected on 0.3-μm millipore filters and the soluble fraction sorbed onto aluminum oxide beds. Sediments were collected by grab sampling or by coring. The radionuclides measured include 239,240Pu and 241Am. The largest source of radionuclides available for transport as indicated by 241Am and 239,240Pu in sediments and water samples reside in the deep water in the northwestern quadrant of the lagoon within approximately 6 km south of the second thermonuclear detonation-Shot Bravo. Small particles and/or ions of radionuclides are released at the sediment-water interface and are transported by the currents. These particles and ions agglomerate during transport away from the sediment surface. Coagulation with detritus and incorporation with plankton would cause the effective particulate size to increase. After about 16 yr, since the last nuclear test on the Atoll, the radionuclides are neither buried totally in the lagoon sediments nor have they been discharged completely to the ocean. There is a constant circulation and redistribution of the materials in the lagoon enforced by prevailing lagoon currents. The flux of americium and plutonium away from Bikini Atoll and into the North Equatorial Current are calculated to be about 3 Ci 241Am and 6 Ci 239,240Pu per year.