The U.S.-based Natural Resources Defense Council (NRDC) estimates that Pakistan has built 24–48 HEU-based nuclear warheads with HEU reserves for 30-52 additional warheads.[9][10] The US Navy Center for Contemporary Conflict estimates that Pakistan possesses between a low of 35 and a high of 95 nuclear warheads, with a median of 60.[11] But these are outdated sources.
The NRDC's and the Carnegie Foundation's estimates of approximately 50 weapons are from 2002–03 estimations. In 2000, US Military intelligence estimated that Pakistan's nuclear arsenal may be as large as 100 warheads.[12] The actual size is hard for experts to gauge owing to the secrecy which surrounds the program in Pakistan. In recent developments, retired Brig. General Feroz Khan, previously second in command at the Strategic Arms Division of Pakistans' Military told a Pakistani newspaper the nation has "about 80 to 120 genuine warheads," and also revealed that Pakistan has decoy or dummy warheads to complicate any designs by aggressors.[13][14]
Pakistan tested plutonium capability in the sixth nuclear test of May 30, 1998 at Kharan. In this test, the latest and most sophisticated bomb design made to be carried by missiles was tested. And it was a very compact, yet powerful device.[citation needed] Compactness is also an issue with F-16s and other fighter-bomber aircraft of the same class, unless the platform happens to be a dedicated strategic bomber. F-16s have limits to the size and weight of the bombs they can carry.
The critical mass of a bare mass sphere of 90% enriched uranium-235 is 52 kg. Correspondingly, the critical mass of a bare mass sphere of Plutonium-239 is 8-10 kg. The bomb that destroyed Hiroshima used 60 kg of U-235 while the Nagasaki Pu bomb used only 6 kg of Pu-239. Since all Pakistani bomb designs are implosion-type weapons, they will typically use between 15-25 kg of U-235 for their cores. Reducing the amount of U-235 in cores from 60 kg in gun-type devices to 25 kg in implosion devices is only possible by using good neutron reflector/ tamper material such as beryllium metal, which increases the weight of the bomb. And the uranium like plutonium is only usable in the core of a bomb in metallic form. Add about 50 or so chemical high-explosive lenses, triggering circuits, and outer aluminum casing, all this adds to the overall weight of the device. Therefore if a bomb has to use only U-235, it will impose serious restrictions on the amount of U-235 that can be used, and the size of the bomb itself, thus restricting its explosive yield. True PAEC did develop bomb designs that could be carried by all PAF aircraft, but after years of effort and R&D, and then too, there were serious limitations on the further extent of miniaturization of the bombs. If Uranium is used as bomb fuel, it cannot be miniaturized beyond a certain point.
However, only 2–4 kg of plutonium is needed for the same device that would need 20–25 kg of U-235. Additionally, a few grams of tritium (a by-product of plutonium production reactors and thermonuclear fuel) can increase the overall yield of the bombs by a factor of three to four.
A whole range and variety of weapons using Pu-239 can be easily built, both for aircraft delivery and especially for missiles (in which U-235 cannot be used). So if Pakistan wants to be a nuclear power with an operational deterrent capability, both first and second strike, based on assured strike platforms like ballistic and cruise missiles (unlike aircraft), the only solution is with plutonium, which has been the first choice of every country that built a nuclear arsenal.
As for Pakistan's plutonium capability, it has always been there, from the early 1980s onwards. There were only two problems. One was that Pakistan did not want to be an irresponsible state and so did not divert spent fuel from the safeguarded KANUPP for reprocessing at New Labs. This was enough to build a whole arsenal of nuclear weapons straight away. So PAEC built its own plutonium and tritium production reactor at Khushab, beginning in 1985. The second one was allocation of resources.
Ultra-centrifugation for obtaining U-235 cannot be done simply by putting natural uranium through the centrifuges. It requires the complete mastery over the front end of the nuclear fuel cycle, beginning at uranium mining and refining, production of uranium ore or yellow cake, conversion of ore into uranium dioxide UO2 (which is used to make nuclear fuel for natural uranium reactors like Khushab and KANUPP), conversion of UO2 into uranium tetrafluoride UF4 and then into the feedstock for enrichment (UF6).
The complete mastery over fluorine chemistry and production of highly toxic and corrosive hydrofluoric acid and other fluorine compounds is required. The UF6 is pumped into the centrifuges for enrichment. The process is then repeated in reverse until UF4 is produced, leading to the production of uranium metal, the form in which U-235 is used in a bomb.
It is estimated that there are approximately 10,000 centrifuges in Kahuta. This means that with P2 machines, they would be producing between 75–100 kg of HEU since 1986, when full production of weapons-grade HEU began. Also the production of HEU was voluntarily capped by Pakistan between 1991 and 1997, and the five nuclear tests of May 28, 1998 also consumed HEU. So it is safe to assume that between 1986 and 2005 (prior to the 2005 earthquake), KRL produced 1500 kg of HEU. Accounting for losses in the production of weapons, it can be assumed that each weapon would need 20 kg of HEU; sufficient for 75 bombs.
Pakistan's first nuclear tests were made in May 1998, when six warheads were tested. It is reported that the yields from these tests were 12 kt of TNT, 30 to 35 kt of TNT and four low-yield (below 1 kt of TNT) tests. From these tests Pakistan can be estimated to have developed operational warheads of 20 to 25 kt and 150 kt of TNT in the shape of low weight compact designs and may have 300–500 kt of TNT large-size warheads. The low-yield weapons are probably in nuclear bombs carried on F-16 Fighting Falcon aircraft and fitted to Pakistan's short-range ballistic missiles, while the higher-yield warheads are probably fitted to the Shaheen and Ghauri ballistic missiles.
The NRDC's and the Carnegie Foundation's estimates of approximately 50 weapons are from 2002–03 estimations. In 2000, US Military intelligence estimated that Pakistan's nuclear arsenal may be as large as 100 warheads.[12] The actual size is hard for experts to gauge owing to the secrecy which surrounds the program in Pakistan. In recent developments, retired Brig. General Feroz Khan, previously second in command at the Strategic Arms Division of Pakistans' Military told a Pakistani newspaper the nation has "about 80 to 120 genuine warheads," and also revealed that Pakistan has decoy or dummy warheads to complicate any designs by aggressors.[13][14]
Pakistan tested plutonium capability in the sixth nuclear test of May 30, 1998 at Kharan. In this test, the latest and most sophisticated bomb design made to be carried by missiles was tested. And it was a very compact, yet powerful device.[citation needed] Compactness is also an issue with F-16s and other fighter-bomber aircraft of the same class, unless the platform happens to be a dedicated strategic bomber. F-16s have limits to the size and weight of the bombs they can carry.
The critical mass of a bare mass sphere of 90% enriched uranium-235 is 52 kg. Correspondingly, the critical mass of a bare mass sphere of Plutonium-239 is 8-10 kg. The bomb that destroyed Hiroshima used 60 kg of U-235 while the Nagasaki Pu bomb used only 6 kg of Pu-239. Since all Pakistani bomb designs are implosion-type weapons, they will typically use between 15-25 kg of U-235 for their cores. Reducing the amount of U-235 in cores from 60 kg in gun-type devices to 25 kg in implosion devices is only possible by using good neutron reflector/ tamper material such as beryllium metal, which increases the weight of the bomb. And the uranium like plutonium is only usable in the core of a bomb in metallic form. Add about 50 or so chemical high-explosive lenses, triggering circuits, and outer aluminum casing, all this adds to the overall weight of the device. Therefore if a bomb has to use only U-235, it will impose serious restrictions on the amount of U-235 that can be used, and the size of the bomb itself, thus restricting its explosive yield. True PAEC did develop bomb designs that could be carried by all PAF aircraft, but after years of effort and R&D, and then too, there were serious limitations on the further extent of miniaturization of the bombs. If Uranium is used as bomb fuel, it cannot be miniaturized beyond a certain point.
However, only 2–4 kg of plutonium is needed for the same device that would need 20–25 kg of U-235. Additionally, a few grams of tritium (a by-product of plutonium production reactors and thermonuclear fuel) can increase the overall yield of the bombs by a factor of three to four.
A whole range and variety of weapons using Pu-239 can be easily built, both for aircraft delivery and especially for missiles (in which U-235 cannot be used). So if Pakistan wants to be a nuclear power with an operational deterrent capability, both first and second strike, based on assured strike platforms like ballistic and cruise missiles (unlike aircraft), the only solution is with plutonium, which has been the first choice of every country that built a nuclear arsenal.
As for Pakistan's plutonium capability, it has always been there, from the early 1980s onwards. There were only two problems. One was that Pakistan did not want to be an irresponsible state and so did not divert spent fuel from the safeguarded KANUPP for reprocessing at New Labs. This was enough to build a whole arsenal of nuclear weapons straight away. So PAEC built its own plutonium and tritium production reactor at Khushab, beginning in 1985. The second one was allocation of resources.
Ultra-centrifugation for obtaining U-235 cannot be done simply by putting natural uranium through the centrifuges. It requires the complete mastery over the front end of the nuclear fuel cycle, beginning at uranium mining and refining, production of uranium ore or yellow cake, conversion of ore into uranium dioxide UO2 (which is used to make nuclear fuel for natural uranium reactors like Khushab and KANUPP), conversion of UO2 into uranium tetrafluoride UF4 and then into the feedstock for enrichment (UF6).
The complete mastery over fluorine chemistry and production of highly toxic and corrosive hydrofluoric acid and other fluorine compounds is required. The UF6 is pumped into the centrifuges for enrichment. The process is then repeated in reverse until UF4 is produced, leading to the production of uranium metal, the form in which U-235 is used in a bomb.
It is estimated that there are approximately 10,000 centrifuges in Kahuta. This means that with P2 machines, they would be producing between 75–100 kg of HEU since 1986, when full production of weapons-grade HEU began. Also the production of HEU was voluntarily capped by Pakistan between 1991 and 1997, and the five nuclear tests of May 28, 1998 also consumed HEU. So it is safe to assume that between 1986 and 2005 (prior to the 2005 earthquake), KRL produced 1500 kg of HEU. Accounting for losses in the production of weapons, it can be assumed that each weapon would need 20 kg of HEU; sufficient for 75 bombs.
Pakistan's first nuclear tests were made in May 1998, when six warheads were tested. It is reported that the yields from these tests were 12 kt of TNT, 30 to 35 kt of TNT and four low-yield (below 1 kt of TNT) tests. From these tests Pakistan can be estimated to have developed operational warheads of 20 to 25 kt and 150 kt of TNT in the shape of low weight compact designs and may have 300–500 kt of TNT large-size warheads. The low-yield weapons are probably in nuclear bombs carried on F-16 Fighting Falcon aircraft and fitted to Pakistan's short-range ballistic missiles, while the higher-yield warheads are probably fitted to the Shaheen and Ghauri ballistic missiles.
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