TRANSPORT OF PLUTONIUM BY RIVERS 689 



distribution of fallout 2 3 9,2 4 0p^j between soluble phases and particles in rivers can 

 probably be approximated by a partition coefficient of about 10~^. The total delivery of 

 dissolved fallout 2 3 9,240py ^^ ^^iq oceans by rivers is probably about lOCi/yr, if we 

 assume a discharge rate for all rivers of about 10^ m^/sec and a concentration of about 

 0.3 fCi/Uter. Since the global average of suspended load in rivers is about 600mg/hter, 

 the transport of fallout 2 3 9,2 4 0p^j ^^ rivers will clearly be dominated by particles. If we 

 assume that the specific activity of all river suspended matter is similar to that of surface 

 soils, the total delivery of fallout 2 3 9,240p^ ^^ ^^le ocean by rivers is about 5 x 10^ 

 Ci/yr, about 50 times the soluble-phase delivery. The specific activity of particles in rivers 

 with very high suspended loads is probably somewhat lower owing to the presence of 

 more large silt- and sand-size particles; so a more reasonable estimate for the total annual 

 delivery of fallout 2 39,240py ^^ ^j^^ ocean by rivers is probably 1 to 5 x 10^ Ci. 



Transport of Plutonium by Rivers Added at Point Sources 



The distribution of fallout 2 3 9,24 Op^ provides information about the partitioning of 

 plutonium between soluble- and suspended-particle phases in rivers and about the 

 processes by v/hich transuranic-element transport occurs in rivers. For point-source 

 addition of plutonium to a river, the most important transport pathway appears to be 

 binding to the suspended load and the mobile portions of the fine-grain sediments and 

 downstream movement with the fine particles. Since the effective concentrations of 

 suspended particles, including the upper few centimeters of fine-grain sediment, in a river 

 will be far greater than 10 to 15 mg/liter, the dominant transport of plutonium would be 

 in association with particles. The kinetics and downstream transport pathways of a 

 particular river system will depend on many factors, such as the frequency and duration 

 of deposition and resuspension episodes for the suspended particles. In the tidal reach of 

 the Hudson, the downstream movement of fine particles tagged with reactor nucHdes is 

 distributed such that some particles require several years to move 50 km whereas others 

 probably require considerably less than a few months. In other rivers, such as the 

 Columbia, which is above tidal influence, the downstream transport of some portions of 

 the suspended load is probably similar to the rate of water transport, whereas other 

 portions of the suspended particles are trapped for long periods, perhaps indefmitely, 

 behind dams. 



The distribution of fallout nucHdes can provide valuable information about which 

 areas of the bottom in a river system are actively scoured and which portions accumulate 

 fme-grain sediments rapidly but probably cannot provide a very detailed picture of the 

 kinetics of downstream transport of fine particles. A tracer added relatively uniformly to 

 the earth's surface, as vras weapons-testing fallout, is not very powerful for providing such 

 information. Fortunately the river systems for which the kinetics of fine-particle 

 movement are most important to understand for predicting transport of transuranic 

 elements are also the ones for which point-source tracers are available. Many nuclear 

 power plants and reprocessing facihties release sufficient quantities of fission or activation 

 products during normal operations which can be used as indicators of fine-particle 

 transport pathways. The behavior of these radioactive tracers cannot be expected to be 

 identical to that of transuranic elements in river systems, but some of these tracers are 

 associated with particles sufficiently to provide very valuable information about the 

 patterns and kinetics of movement and accumulation of fine particles of most importance 

 for evaluating the transport pathways of point-source releases of transuranic elements. 



