Pakistan Nuclear Stockpile
If Pakistan's stockpile was about 75 weapons in 2004, by 2018 that number had probably tripled to over 225 weapons. Assuming an average production of about six bombs each year, by 01 January 2004 Pakistan's uranium bomb stockpile was about sixty weapons, and by 2020 it may have grown to about 100 bombs. Assuming an average production of about 2.5 plutonium bombs each year, by 01 January 2004 Pakistan's plutonium bomb stockpile was probably about fifteen weapons. Between 2010 and 2014 Pakistan added three further plutonium production reactors, which would allow nuclear weapons to be produced at a rate of about a dozen weapons per year [about half the 19-26 weapons per year initially assessed]. By the year 2020 Pakistan might have 120 plutonium bombs.
According to some reports, Pakistan's nuclear weapons were initially kept in an unassembled state, with the fissile core kept separate from the bomb assembly. The bomb components and the wider infrastructure are under military control.
As of the mid-1990s it was widely reported that Pakistan's stockpile consisted of as many as 10 nuclear warheads based on a Chinese design. As of mid-1998 estimates of Pakistan's HEU inventory ranged between 100 and 500 kilograms. Assuming that Pakistan would need about 20 kilograms for a single weapon, Pakistan's stockpile might be estimated at between 5 and 25 weapons. By the end of the decade, it was reliably reported that Pakistan's stockpile consisted of about 30 nuclear weapons.
Pakistan's stockpile of weapons material is essentially from the centrifuge-based uranium enrichment facility at Kahuta. The stockpile as of 1991 was various estimated at 160 to 260 kg. If it had not stopped at that point, the amount would be 460 to 785 kg by 1999. About 1991, Pakistan installed additional centrifuges, raising its HEU production capacity roughly threefold. Assuming about 20 kg of HEU for a device, Pakistan would have have had 10 to 15 bombs as of 1991, and 25 to 40 bombs by 1999 if it had not stopped enrichment in the 1991-1998 period. Although there have been reports that Pakistan acquired a tritium production unit from Germany and had tritium extracted from heavy water with French help in the late 1980s, there is no evidence as yet that it has acquired thermonuclear capability. Although Pakistan has a plutonium reprocessing plant based on French design, as of 1999 it was not yet to become operational. [Nuclear and Missile Race in South Asia: Relevance of Military Restructuring By Dr. Vinay Kumar Malhotra]
While Pakistan's main uranium enrichment facility is at Kahuta, smaller uranium enrichment facilities exist at Sihala and Golra. Pakistan also has a new enrichment facility near Wah, designated the Gadwal Uranium Enrichment Plant by the US government. The production capacity of this facility is not attested by open sources, and is not reflected in published stockpile estimates.
As of late 2001 it was reported that the US Government estimated that Pakistan had fabricated fewer than 20 complete nuclear weapons, based on a design that uses uranium. It was estimated that Pakistan had produced sufficient weapons-grade uranium to fabricate twice this many uranium weapons. It was also estimated that Pakistan's production of plutonium was sufficient to fabricate at least five weapons. However, at least one [anonymous] former US government official suggested that these estimates of were "almost certainly way, way low." [New York Times December 9, 2001, Pg. 1]
An estimate published in late 2001 suggested that Pakistan might have accumulated between 40 and 45 nuclear weapons by 2000, primarily using highly enriched uranium (HEU), but with small additions beginning in 1999 of plutonium from Khushab. These figures suggested that Pakistan could have been adding nuclear weapons from uranium and plutonium, respectively, at the rate of about 5.5 and 1.5 annually. [MINIMUM NUCLEAR DETERRENCE POSTURES IN SOUTH ASIA: AN OVERVIEW OCTOBER 1, 2001 - DEFENSE THREAT REDUCTION AGENCY ADVANCED SYSTEMS AND CONCEPTS OFFICE, PREPARED BY: RODNEY W. JONES]
Pakistan probably requires 15-20 kg of highly enriched Uranium per weapon. Kahuta can probably produce about 110 kg of HEU [between 80 kg to 140 kg] annually, enough for at least four bombs, and possibly as many as eight bombs each year. Pakistan probably produced about 200 kg at Kahuta through the end of 1991, at which time it ceased production under a moratorium urged by the US Government. Pakistan probably resumed uranium enrichment at Kahuta in 1998, and has probably been producing HEU and bombs since that time. As of 01 June 1998 one estimate concluded that by the end of 1998 Pakistan's inventory of weapons grade uranium could increase to 600 kg, or enough for 30 weapons. [Pakistan's Nuclear Stockpile By David Albright and Kevin O'Neill, Institute for Science and International Security, June 1, 1998 ] Assuming an average of about six bombs each year, this would suggest that by 01 January 2004 Pakistan's uranium bomb stockpile was about sixty weapons.
The Khushab plutonium production reactor could produce 10-15 kg of plutonium annually, or enough material for 2 to 3 bombs. In April 1998 Pakistan announced that it had "commissioned" this 50-70 megawatt (MW) reactor which probably became fully operational in the 1999 time-frame. Assuming an average of about 2.5 plutonium each year, this would suggest that by 01 January 2004 Pakistan's plutonium bomb stockpile was about fifteen weapons.
In 1988 the US and Pakistan reached an informal understanding, which according to US officials went into effect in 1993, under which Pakistan agreed to freeze production of bomb-grade HEU indefinitely, and to refrain from enriching uranium to a level above 20% U-235. Prior to the 1998 nuclear tests, the US had reportedly obtained intelligence indicating that Pakistan had stopped production of bomb-grade uranium.
Prior to the 1998 nuclear tests, the US had reportedly obtained intelligence indicating that Pakistan had stopped production of bomb-grade uranium. However, following the tests A.Q. Khan claimed that Pakistan had never stopped making bomb-grade HEU during the 1980s and 1990s, and reportedly US officials said "we don't have enough information" to conclude that Pakistan was not making weapons-grade HEU.
Pakistan stated that all the devices tested used only highly enriched uranium (HEU). According to a preliminary analysis conducted at Los Alamos National Laboratory, material released into the atmosphere during an underground nuclear test by Pakistan in May 1998 contained low levels of weapons-grade plutonium. But Lawrence Livermore National Laboratory and other agencies contested the accuracy of this finding. The significance of the Los Alamos finding was that Pakistan had either imported or produced plutonium undetected by the US intelligence community.
An August 2015 joint study by the Carnegie and Stimson research organizations estimated that Pakistan has the capability to produce 20 nuclear warheads annually while its archrival, India, appeared to be producing about five warheads.
Pakistan’s chief negotiator on 12 February 2016 dismissed reports its nuclear arsenal program was the world’s fastest growing, and repeated Islamabad’s demand that it be inducted into a club of nuclear trading nations. “I think it would be important for us to distinguish between what is propaganda, disinformation and motivated reporting. Pakistan is not in an arms race,” asserted Foreign Secretary Aizaz Chaudhry, addressing a gathering of experts, officials and foreign diplomats in the Pakistani capital. “Pakistan only goes for credible minimum deterrence. We have every right as a state for self-defense. Our nuclear deterrence is for self-defense. It is not status driven,” said Chaudhry.
Zia Mian et al concluded in 2009 that "by 2020, Pakistan could have accumulated approximately 450 kg of plutonium from the Khushab reactors and 2500–6000 kg of highly enriched uranium (HEU) (90 percent enriched) for enrichment capacities ranging from 15,000–75,000 SWU. These stocks would be sufficient for perhaps 100–240 simple fission weapons based on HEU and for 90 plutonium weapons. Pakistan may be able to produce more weapons if it either increases its rate of uranium mining or has more advanced weapon designs requiring less fissile material in each weapon."
This is a somewhat simplified rehearsal of stockpile architecture, since it is highly likely that Pakistan's fissile material, like that of other nuclear weapons states, would be used to build technically sweet two-stage tandem-implosion hydrogen bombs. [“When you see something that is technically sweet, you go ahead and do it and you argue about what to do about it only after you have had your technical success. That is the way it was with the atomic bomb.” — J. Robert Oppenheimer]. Under this plausible assumption, the key figure of merit is the amount of plutonium available for the fission implosion triggers, with the uranium used for the fusion implosion.
The Mian et al estimate was made based on three plutonium production reactors at Khushab, when in fact a fourth, larger, reactor probably came on line aroung 2015, and a fifth reactor of equal size may come on line around the year 2020. These two new reactors, not considered by Mian et al, would more than double Pakistan's plutonium production. Mian et al concluded that the initial three reactors would consume all the readily availible uranium production, though they identified some approaches to increasing uranium supply.
Plutonium fission triggers are variously estimated to require between two and four kilograms of Plutonium. The 450 kg of Plutonium estimated by Mian et all would thus yield at least 110 bombs, but not more than 225 bombs. After the year 2020, with annual plutonium production incresing from the 20 kg / year used in Mian et al, to a total of about 50 kg per year, Pakistan could add a further one to two dozen hydrogen bombs each year.
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