1.1 Nuclear Weapons

Nuclear weapons tests account for a significant proportion of the total activity released into the environment and historically are the major source of radio­nuclides in the atmosphere. An estimated 2 x 108 TBq of radioactivity have been released into the atmosphere as a result of nuclear weapons testing;3 Table 1 lists the radionuclides produced and released by atmospheric nuclear tests.4 Most of the radionuclides released were short-lived, and so atmospheric levels of radioactivity have declined sharply from their peak in the 1960s; further decline in levels of radioactivity will be much slower, as the remaining activity is predominantly due to long-lived 14C.4 Fallout from atmospheric weapons testing will also cause contamination of surface water and terrestrial environments. Fallout can either be local (within a few 100 km of the test site), regional (up to several thousand km from the site) or global, and the spread of fallout will depend on the altitude and latitude of the explosion and the explosive yield.5,6

Although much of the contamination arising from nuclear weapons testing is widely dispersed and at low levels, there are considerable levels of activity at test and production sites. In the USA, there are >70 million m3 of con­taminated soil and > 1800 million m3 of contaminated water at Department of Energy facilities used for weapons production.7 At the Mayak Production Association in the Chelyabinsk region, Russia, weapons-grade plutonium was produced for в 40 years and significant levels of contamination exist at the site and the surrounding area from both production and accidental discharges.8,9 Approximately 105 TBq of radioactivity, as liquid waste, were discharged from the site into the Techa River between 1949 and 1956, with most of the released radioactivity associated with 89+90Sr (20.4%), 137Cs (12.2%), rare earth isotopes (26.8%), 95Zr-95Nb (13.6%) and ruthenium isotopes (25.9%).9,10 At the same site ~ 7.4 x 104 TBq of radioactivity were released as a result of a high level radioactive liquid waste tank exploding, causing the contamination of

~20 000 km2 at concentrations > 4000 Bq m 2.8,11 Underground weapons test­ing has caused contamination of the subsurface with tritium, fission and acti­vation products and actinides.2,12 At the Nevada Test site, the primary location for nuclear weapons tests in the USA, ~1 x 107TBq of radioactivity was released into the subsurface during 828 tests.13 The decay-corrected radionuclide inven­tory as of 1992 (the year of the last test) is 4.86 x 106 TBq, with the most sig­nificant amounts of radioactivity arising from 3H, 137Cs, 90Sr, 241+239Pu, 85Kr, 152+154Eu and 151Sm.14 The inventory will change, however, as short-lived radionuclides decay and daughter radionuclides appear; with time, the remain­ing radionuclide inventory in the subsurface will be dominated by long-lived radionuclides such as uranium, plutonium, neptunium and americium.14