The Prime Minister's visit may mark the completion of work on Pakistan's second plutonium production reactor. Khushab is the home of the country's first plutonium production reactor (Khushab-I), which started work in 1998, and is the site where two new reactors are under construction. The construction of Khushab II appears from satellite imagery to have started in 2001-2002, while work on Khushab III seems to have started in 2005 or 2006.
The two new reactor buildings appear to be identical to each other but different from Khushab-I and there has been a debate whether the new reactors are much more powerful than the 50 MWt Khushab-I reactor. However, Khushab-II seems to have cooling towers similar to those of Khushab-I suggesting they are of comparable power. The New York Times reported U.S. government sources as suggesting that "the emerging reactor appeared to be roughly the same size as the small one [i.e. Khushab-I] Pakistan currently uses to make plutonium for its nuclear program."
If Khushab-II is the same power as Khushab-I, and both continue to operate, then Pakistan will be able to double its current rate of plutonium production for weapons. Together the two reactors, operating at 70 percent capacity, would produce about 22 kg of weapon grade plutonium per year.
The plutonium from Khushab-II would become available about a year after the reactor comes on-line, allowing time to irradiate the fuel and then cool it before reprocessing it to separate the plutonium.
UPDATE 03/24/10: ISIS published an analysis of satellite images that show steam in the cooling towers of the Kushab-II reactor. This indicates that the reactor was operating in December 2009, when the image was taken.
(For more on Pakistan and India's nuclear weapon programs and Pakistan's demands for a US-Pakistan nuclear deal similar to the US-India deal, see IPFM Research Report.)