Khushab / Khusab
The heavy water plutonium production reactors complex at Khushab is a central element of Pakistan's program for the production of plutonium and tritium for advanced compact warheads. The Khushab facility, like that at Kahuta, is not subject to IAEA inspections. The first reactor at Khushab, with a capacity variously reported at between 40 MWT to 50 MWT [and as high as 70 MWT], was "commissioned" in March 1996, and had been under construction with Chinese assistance since the mid-1980s. According to a Pakistani press report ["Pakistan's Indigenous Nuclear Reactor Starts Up," Islamabad The Nation, April 13, 1998], the Khushab plutonium production reactor had gone critical and began operating in early 1998.
Plutonium is the preferred material for building light, sophisticated warheads, since highly enriched uranium (HEU) generally results in bulkier weapons. Prior to the start-up of Khushab, Pakistan was dependent on the production of highly enriched uranium at Kahuta. The Khushab reactor provides Pakistan the ability to produce enough plutonium each year to fabricate at least one bomb, and perhaps as many as three to five bombs [depending on the efficiency of the bomb design and the reactor's actual output].
The actual plutonium output of the first reacator at Khushab was dependent on both the thermal power level, as well as the actual operating time. Pakistan's prior history of operating the Karachi Nuclear Power Plant (KANUPP), for many years Pakistan's only working nuclear power plant, suggests that the Khushab reactor may have a rather low operating availability. According to the International Atomic Energy Agency, the KANUPP lifetime energy availability factor (as of the end of 1997) was 28.6%, one of the worst performing nuclear power plants in the world. For the period 1989-1996 KANUPPís capacity factor (the ratio of actual electrical production versus designed power) was only 34%. Although the CANDU reactor at KANUPP is of different design than Khushab, this history suggests that Khushab may produce substantially less plutonium than its theoretical capacity.
Pakistan initially sought to produce plutonium weapons, but these plans were frustrated with the 1977 cancellation by France of the planned sale of a reprocessing plant at Chasma. As of 1995 the US Government had no indication that Pakistan had the capability to reprocess plutonium. According to a 14 September 1996 CIA report, the China Nuclear Energy Industry Corporation sold a special industrial furnace and high-tech diagnostic equipment. It was subsequently reported that the equipment was intended for the Khushab facility. High temperature furnaces are used to mold uranium or plutonium.
Pakistan succeeded in illicitly acquiring a tritium purification and storage plant, and tritium precursor materials from two German firms. It is estimated that plutonium spiked with a few grams (3-4 g) of tritium can yield an explosion 300%-400% larger than normal.
The United States apparently obtained a commitment from China not to supply the heavy water necessary to start up this unsafeguarded plutonium production reactor. But in March 1998 it was reported that China had supplied Pakistan with far more heavy water than needed to operate the safeguarded Kanupp nuclear power reactor, suggesting that Pakistan would be able to divert heavy water from the civilian plant to the Khushab military plant. Although these concerns received considerable political attention in the late 1990s, it is evident from IKONOS satellite imagery that the Khushab complex includes a heavy water production facility.
Khushab Reactor II
Pakistan began construction of the second heavy water reactor at the Khushab site sometime between March 2000 and 2002. The new reactor was estimated by some to be able to operate in excess of 1,000 megawatts-thermal, but Pakistani officials have not released any confirmatory information. More conservative estimates put its output in the range of 70-130 MWT.
As of September 2008, eight mechanical draft (fan-driven) cooling towers had been built, and additional mechanical draft cooling tower units were under construction. This indicates the second reactor could be larger than the original one. Furthermore, two additional towers that are not present at the original reactor site have been constructed. The second site is believed to have been completed as of January 2009. Steam was seen rising from the cooling towers fan blades on December 31, 2009, indicating the reactor was in some stage of initialization. On February 20, 2010, Prime Minister Gilani visited the Khushab-II site to congratulate Khushab engineers for completing several important projects and helping to reinvigorate Pakinistanís economy. This would seem to indicate the second reactor was running at that time.
Khushab Reactor III
Construction on Pakistanís third heavy water reactor at Khushab began in 2006 and appeared to be progressing much more quickly than the second reactor. By September 9, 2010, construction looked to be nearing its end as a row of cooling towers (also mechanical draft) had been completed. As at the second reactor site, two tall buildings were built adjacent to the reactor. Similarities in the construction of the third and second reactors indicate they will have similar power levels.
Khushab Reactor IV
Satellite imagery of the Khushab reactor site on January 15, 2011 showed signs of what appeared to be construction of another heavy water reactor. This would be the fourth reactor at the Khushab site, and the third built since 2000. Significant progress had been made at the site as of April 20, 2011. The new reactor was initially believed to be a duplicate of the second and third reactors. But it was subsequently seen as being rather larger, with a megawatt-thermal output of 70-130 MWT.
Khushab Reactor V
Wikipedia reports "A further reactor has been speculated on (Khushab-V). Space-based surveillance has not turned up signs that work has begun yet on any fifth plutonium reactor at Khushab, although construction of major facilities continues." In January 2015 ISIS highlighted that new construction activity was taking place in the southwest corner of Pakistanís Khushab nuclear site, south of reactors 2, 3, and 4. At the time, ISIS speculated that the site could be for another reactor.
Indeed, Google Earth imagery discloses a partially complete reactor, with a configuration generally similar to that of Khushab IV, though with a different orientation. Each of the Khushab reactors has a bank of cooling towers of unique configuration. As is well known, reactor thermal power may be estimated based on the size of these cooling towers [John Pike, Tim Brown and Charles Vick were the first open source analysts to apply this principle, in their work on the Israeli Dimona reactor in the late 1990s]. The devil is in the details, but in round numbers of the area of the fifth reactor cooling towers [ about 14 meters by about 90 meters, yielding a surface area of about 1250 meters2] is about the same as that of the fourth reactor [ about 11 meters by about 110 meters, yielding a surface area of about 1150 meters2]. Both are about twice the size of the early reactors [about 500 meters2]. So the power of Khushab V is probably about the same as that of Khushab IV, about 90 megawatts-thermal (MWth).
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