88 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



square framework about 22 by 22 ft (7 by 7 m) in cross section and extending high 

 enough that the explosion fireball did not reach the ground surface. This meant that most 

 towers were between 300 and 500 ft (90 and 150 m) high (Glasstone, 1962); the tallest 

 was 700 ft (213 m). Steel guy wires gave these towers lateral support. When a nuclear test 

 was fired, the great heat vaporized much of the tower steel and carried it upward v^thin 

 the rapidly rising cloud. As the vaporized tower material cooled, it condensed, and most 

 of it tended to fall nearby, carrying along with it some of the residual transuranic 

 materials from the tested device which were condensing at the same time. 



Balloon-suspended nuclear tests and airdropped nuclear tests, which were detonated 

 well above the ground, contributed very little material to which the residual transuranic 

 materials might become attached. Hence probably a fairly large fraction of the 

 transuranic material from those tests became widely dispersed throughout the world. 



Much of the material that was released into the environment from nuclear testing has 

 by today become relatively inaccessible to the environment. That which fell on the lakes, 

 oceans, and seas is in the process of sinking to the bottom or already has reached the 

 bottom sediments (Edgington, Wahlgren, and Marshall, 1976), and much of that which fell 

 on land areas will soon be beneath the immediate surface layer (Essington and Fowler, 

 1976). Because of these factors and because of the fairly large uncertainties as to the 

 amounts of transuranic materials that originally had been injected into the world 

 environment from nuclear weapons testing, quantitative (source-term) estimates based on 

 weapons testing history may not be as useful in handling specific localized problems as 

 are regional estimates of the materials present based on local samplings. 



On the other hand, regional estimates may not extrapolate well as a means of 

 determining the world source term. Environmental releases of transuranics from nuclear 

 weapons have varied considerably by latitude and have been far greater in the northern 

 hemisphere than in the southern hemisphere. If we should assume that the U. S. 

 plutonium distribution level (Harley, 1971) in the surface soils of about 1 mCi/km^ 

 persists worldwide (about 4.8 x 10^ km^), there would be 480,000 Ci, or about 

 8,000 kg. Hardy, Krey, and Volchok (1973) have estimated that worldwide there was 

 325,000 Ci, or about 5200 kg, of ^^^Pu and ^"^^Pu in weapons-fallout debris. Although 

 quantities of transuranics in this range are entirely credible, my review of atmospheric 

 nuclear testing indicates that those estimates may be somewhat high. All things 

 considered, a 1 x 10^ Ci source term for environmentally available ^^^Pu, although very 

 approximate, appears conservatively suitable. 



As mentioned, there is some transuranic material in the environment as a result of 

 accidents with nuclear weapons. A certain amount of this transuranic dispersal took place 

 as the result of deliberate tests of the behavior of weapons under accident conditions.* 

 Several such accident-simulation tests were done at and near the Nevada Test Site and at 

 the Tonopah Test Range near Tonopah, Nev. Although there was on the order of 10 to 

 10^ Ci of plutonium (total) involved in those tests, some of the material was recovered 

 and removed from the environment by personnel manually searching for and picking up 

 the scattered metal pieces. On the basis of site -in tensive inventories at the locations of 

 these safety tests (White and Dunaway, 1975) conducted under the NAEG studies 

 program, about 160Ci of ^^^Pu and ^"^^Pu remain environmentally available (in the 



*U. S. nuclear weapons are designed so that no accident can create the nuclear circumstances 

 necessary to deUver nuclear yield. However, certain accident conditions could cause the materials 

 associated with a nuclear device to burn or detonate and thus disperse transuranic materials. 



