My colleague, Tamara Patton, has published her much anticipated master’s thesis on estimating the size of the Pakistani plutonium production reactors at Khushab in Science and Global Security  (Combining Satellite Imagery and 3D Drawing Tools for Nonproliferation Analysis: A Case Study of Pakistan’s Khushab Plutonium Production Reactors).  It’s one heck of a paper and available for free.

I asked Tamara to trace one of the policy implications that didn’t make the final cut of the paper — and she kindly agreed, writing this fascinating little piece about Pakistan’s shrinking supply of uranium:

Uranium Fuel Constraints for Pakistan’s Nuclear Weapon Complex

Tamara Patton, December 2012

 As construction on a fourth reactor at Pakistan’s weapons-grade plutonium production complex at Khushab continues apace, an important question is where the government plans to get the uranium needed to fuel its growing fleet of reactors.

The answer cannot be ‘Pakistan’ for much longer, at least not without severe difficulties. Pakistan is not a signatory to the Nonproliferation Treaty, which complicates the import of uranium. Pakistan has been able to secure Chinese LEU fuel assemblies for the Chasma Nuclear Power plants and a limited stock of safeguarded natural uranium fuel assemblies for the Karachi Nuclear Power Plant (KANUPP).  However, as Canada stopped supplying Pakistan with fuel assemblies for KANUPP in 1976, this stock is most likely gone by now, causing KANUPP to rely on domestic stocks of uranium in recent decades.  The weapons program, including military HEU production and fabrication of fuel for the reactors at Khushab, must also rely on domestic production. Pakistan’s Bagalchore mine was reportedly exhausted and closed by 2000, so uranium resources now only come from the Qabul Khel mine (opened in 1992), the Nanganai deposit (1996), and Taunsa deposits (2002), all using in situ leaching.  Current domestic production estimates from these sources stand at 40 tons of uranium per year.

A 2009 study by Mian, Nayyar, and Rajaraman estimates that when applied to the fueling of the Khushab fleet of reactors, the 40 tons per year amount alone can only support approximately 150 MWt of total reactor capacity operating at 70 percent efficiency and a low burnup of 1000 MWd/ton.  Forty tons would just barely support the first three reactors.  Today, there is a fourth.

In my recent paper, Combining Satellite Imagery and 3D Drawing Tools for Nonproliferation Analysis: A Case Study of Pakistan’s Khushab Plutonium Production Reactors, I sought to refine maximum thermal capacity estimates of the reactors based on 3D analysis of each reactor’s cooling towers (snapshot below).  Using these estimates, the table here shows how the completed four reactors at Khushab would operate at around a total of 200 MWt at 70 percent efficiency, which translates to a requirement of as much as ~70 tons of uranium per year.  The reactor capacity estimates in my paper are upper limits based on cooling capacity.  Seventy tons of uranium is therefore also an upper limit.  The reactors could be slightly smaller, with overdesigned cooling systems, or Pakistan may plan to operate the reactors at a lower capacity.  Still, Pakistan appears likely to run a uranium deficit, perhaps as much as 30 tons, that could exhaust uranium stocks and eventually the deposits themselves.


Building the Khushab reactors in Google SketchUp to estimate reactor thermal capacity and plutonium production capabilities. See Science and Global Security v.20 no. 2.

If Pakistan runs a consistent uranium deficit, the demand for fuel for the Khushab reactors may begin to starve Pakistan’s enrichment complex for HEU production.  The construction of a fourth plutonium production reactor in the face of limited uranium resources seems to signal a shift in Pakistan’s priorities from larger uranium-based to smaller plutonium-based nuclear warheads.  I estimate that the four reactors at Khushab could eventually produce between 60-70 kg of plutonium per year – enough for 10-20 warheads per year, depending on how plutonium is used in each warhead.  This is a significant capacity, and the quick pace of construction at Khushab is one indicator that Pakistan’s resources may be gravitating to this site.  Nevertheless, it’s too soon to rule out the continued production of uranium-based weapons in the future.

But where will Pakistan turn for more uranium if needed?  One possibility is that it can use as feed its accumulated depleted tails in addition to reprocessed uranium.  For every one ton of depleted uranium (with 0.2%U-235), Pakistan could re-enrich it to acquire approximately 0.27 tons of uranium with the 0.7% U-235 content of natural uranium needed to fuel the Khushab reactors. [Author’s correction: 0.2% U-235 is correct only for some PHWRs.  The number for Khushab should be around 0.6%.  See page 87 of this report for Alexander Glaser’s calculations on the isotopic composition of spent fuel from a low-burn-up 40 MWt heavy water reactor.]  Considering that Pakistan has been enriching uranium since around 1978, this is a not an inconsiderable amount.  Spent fuel from heavy water reactors like Khushab also contains about 0.2% U-235, and Pakistan may possess the capability to reprocess this material at its New Labs facility.

Another interesting possibility is the extraction of uranium from rock phosphate, which according to this report produced in Pakistan can contain anywhere from 0.005-0.04% U3O8, or yellowcake.  Phosphoric acid, obtained from phosphate rock, is the basic ingredient in di-ammonium phosphate (DAP), one of the most commonly used fertilizers in the world. According to these statistics by Pakistan’s National Fertilizer Development Centre, domestic production of DAP began in 1999.

Uranium should be removed from the phosphoric acid before it is converted to fertilizer, lest it end up in the final consumer products and pose a health hazard.  This can be done in a variety of ways, as described in this 1987 IAEA report.  Although less economical than mining, uranium extracted from phosphates prior to fertilizer production is potentially a significant source of uranium for a weapons program.  Not surprisingly, Syria was recently very interested in this process.

 Along with the fact that phosphoric acid is widely traded for the production of fertilizer, it is also not subject to heavy scrutiny through export controls.  Morocco in particular is a major exporter of phosphoric acid as it holds nearly 77% of worldwide phosphate rock reserves.  In recent years, Pakistan and Morocco have established a joint venture to ensure “uninterrupted supply” of phosphoric acid to Pakistan on a large scale. Export of phosphoric acid, a legitimate commodity, is not prohibited and there is no evidence that the joint venture is supporting Pakistan’s nuclear weapons program or engaged in any nefarious activities.  An important question is how much uranium may be inadvertently transported through the trade of phosphoric acid for DAP production.  This study shows how appreciable amounts of uranium present in processed phosphate rocks can pass into phosphoric acid and then to fertilizers.  Of all the materials tested in the study, DAP fertilizer is shown as possessing the highest end concentration of uranium: about 52 mg/kg.  Theoretically speaking, many factors could affect how much uranium Pakistan could acquire through the production of DAP.  Factors such as the uranium content of the original phosphate rock, the purity of the phosphoric acid received in Pakistan, and the method of extraction used to acquire the uranium would all affect the final amount of uranium.  Whatever the case may be, this is a potentially significant source of uranium for Pakistan, one that bears close scrutiny.

Reactor Thermal power estimate at 70% capacity factor (MWt) Operational days per year (days) Burnup (MWd/ton) U required per year (tons)
Khushab I 34 365 1000 12
Khushab II 46 365 1000 17
Khushab III 57 365 1000 21
Khushab IV 57 365 1000 21
                                                     Total U required per year 71

Estimated uranium fuel requirements for the Khushab reactors based on reactor thermal capacity estimates derived from limits of the cooling towers.