<P> This definition is inclusive of "zero yield" safety tests of warheads, whether the test is successful (there is no nuclear yield) or the test is unsuccessful (there is a nuclear yield). It does not include hydronuclear, cold or subcritical tests because no nuclear explosions are possible, even in failure . In these sorts of tests there may be small amounts of chain reaction occurring, but they stop before materially adding to the chemical explosion that causes them . The line here is finely drawn, but, among other things, subcritical testing is not prohibited by the Comprehensive Nuclear Test Ban Treaty, while safety tests are . </P> <P> The table in this section summarizes all worldwide nuclear testing (including the two bombs dropped in combat which were not tests). The country names are links to summary articles for each country, which may in turn be used to drill down to test series articles which contain details on every known nuclear explosion and test . The notes attached to various table cells detail how the numbers therein are arrived at . As of 1993, worldwide, 520 atmospheric nuclear explosions (including 8 underwater) have been conducted with a total yield of 545 megaton (Mt): 217 Mt from fission and 328 Mt from fusion, while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 is 1,352 explosions with a total yield of 90 Mt . </P> <Table> Worldwide nuclear testing totals by country <Tr> <Th> Country </Th> <Th_colspan="2"> Tests </Th> <Th> Devices fired </Th> <Th> Devices w / unknown yields </Th> <Th> Peaceful use tests </Th> <Th> Non-PTBT tests </Th> <Th> Yield range (kilotons) </Th> <Th> Total yield (kilotons) </Th> <Th> Percentage by tests </Th> <Th> Percentage by yield </Th> </Tr> <Tr> <Th> USA </Th> <Td> 1032 </Td> <Td> </Td> <Td> 1132 </Td> <Td> 12 </Td> <Td> 27 (Operation Plowshare) </Td> <Td> 231 </Td> <Td> 0 to 15,000 </Td> <Td> 196,514 </Td> <Td> 48.7% </Td> <Td> 36.3% </Td> </Tr> <Tr> <Th> USSR </Th> <Td> 727 </Td> <Td> </Td> <Td> 981 </Td> <Td> 248 </Td> <Td> 156 (Nuclear Explosions for the National Economy) </Td> <Td> 229 </Td> <Td> 0 to 50,000 </Td> <Td> 296,837 </Td> <Td> 34.4% </Td> <Td> 54.9% </Td> </Tr> <Tr> <Th> UK </Th> <Td> 88 </Td> <Td> </Td> <Td> 88 </Td> <Td> 31 </Td> <Td> 0 </Td> <Td> 64 </Td> <Td> 0 to 3,000 </Td> <Td> 9,282 </Td> <Td> 4.15% </Td> <Td> 1.72% </Td> </Tr> <Tr> <Th> France </Th> <Td> 217 </Td> <Td> </Td> <Td> 217 </Td> <Td> 0 </Td> <Td> </Td> <Td> 57 </Td> <Td> 0 to 2,600 </Td> <Td> 13,567 </Td> <Td> 10.2% </Td> <Td> 2.51% </Td> </Tr> <Tr> <Th> China </Th> <Td> 47 </Td> <Td> </Td> <Td> 48 </Td> <Td> 7 </Td> <Td> 0 </Td> <Td> 23 </Td> <Td> 0 to 4,000 </Td> <Td> 24,409 </Td> <Td> 2.22% </Td> <Td> 4.51% </Td> </Tr> <Tr> <Th> India </Th> <Td> </Td> <Td> </Td> <Td> 6 </Td> <Td> 0 </Td> <Td> </Td> <Td> 0 </Td> <Td> 0 to 60 </Td> <Td> 68 </Td> <Td> 0.141% </Td> <Td> 0.0126% </Td> </Tr> <Tr> <Th> Pakistan </Th> <Td> </Td> <Td> </Td> <Td> 6 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 1 to 32 </Td> <Td> 51 </Td> <Td> 0.107% </Td> <Td> 0.0094% </Td> </Tr> <Tr> <Th> North Korea </Th> <Td> 6 </Td> <Td> </Td> <Td> 6 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 0 </Td> <Td> 1 to 250 </Td> <Td> 197.8 </Td> <Td> 0.283% </Td> <Td> 0.024% </Td> </Tr> <Tr> <Th> </Th> </Tr> <Tr> <Th> Totals </Th> <Td> 2121 </Td> <Td> </Td> <Td> 2476 </Td> <Td> 294 </Td> <Td> 188 </Td> <Td> 604 </Td> <Td> 0 to 50,000 </Td> <Td> 540,849 </Td> <Td> </Td> <Td> </Td> </Tr> </Table> <Tr> <Th> Country </Th> <Th_colspan="2"> Tests </Th> <Th> Devices fired </Th> <Th> Devices w / unknown yields </Th> <Th> Peaceful use tests </Th> <Th> Non-PTBT tests </Th> <Th> Yield range (kilotons) </Th> <Th> Total yield (kilotons) </Th> <Th> Percentage by tests </Th> <Th> Percentage by yield </Th> </Tr>

How many nuclear bombs have been set off
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