WASHINGTON, July 24: The United States said on Monday it was aware that Pakistan is building a powerful new nuclear reactor and urged Islamabad not to use the facility for military purposes.

“We have been aware of these plans and we discourage any use of that facility for military purposes such as weapons development,’ White House spokesman Tony Snow told reporters. “Pakistan of course is outside the non-proliferation treaty and, therefore, they do develop their capabilities independently,” Mr Snow said.

A US think-tank reported earlier Monday that Pakistan had started work on a new reactor that could signal a major expansion of the country’s nuclear weapons capabilities “Commercial satellite imagery suggests Pakistan is building a second, much larger plutonium production reactor inside the Khushab complex,” said the Washington-based Institute for Science and International Security. Diplomatic observers in Washington say that the timing of release is significant, because it raises fresh concerns about an arms race in South Asia at a time when the US Congress is on the verge of ratifying a deal which would give India greater access to American civilian nuclear technology.

In an analysis based on the diameter of the vessel, the institute estimates that the under-construction reactor is capable of operating in excess of 1,000 megawatts-thermal. Such a reactor could produce over 200 kilograms of weapon-grade plutonium per year, assuming it operates at full power for a modest 220 days per year. At 4-5 kilograms of plutonium per weapon, this stock would allow the production of over 40-50 nuclear weapons a year, the report says. A separate assessment by Washington-based nuclear experts concludes that this would represent a 20-fold increase from Pakistan’s existing capabilities.

“Reactors of this size should lend further support to the fissile material capacity,” Paul Brannan, one of the co-authors of the report told Dawn when asked why believes this reactor is not meant to produce energy.

The reactor could also be used to produce substantial amounts of tritium for boosted fission weapons, the report adds.

Along with the report the institute also published two close ups of the building suspected to be a large heavy water, plutonium production reactor.

“South Asia may be heading for a nuclear arms race that could lead to arsenals growing into the hundreds of nuclear weapons, or at minimum, vastly expanded stockpiles of military fissile material,” the institute’s David Albright and Paul Brannan conclude in the report.

The ISIS claims that the construction of the reactor started after March 2000. In the image from June 2005, a possible reactor vessel is visible within the inner portion of the building. The support columns for the outer portion of the building are visible as well. A large crane is visible just outside the building. Situated to the west of the main building is a structure suspected to be a mosque. It is the only building within the Khushab site with walls that are not parallel to those of other buildings and appears to face Mecca.

In an April 2006 image, the outer portion of the building has been covered with a roof. Across the ground next to the new crane are what appear to be several arched metal rods. These pieces could be used as the frame for a roof on top of the inner structure. The linear distance between the ends of the arched rods and the distance between the east and west walls of the inside structure are both approximately 105 feet.

The construction activity just above the north-east corner of the entire building could be the foundation for a stack.

The round object inside the building has a diameter of about five meters. This is significantly larger than the corresponding vessel in the existing reactor at this site.

Based on the size of the vessel, assuming moderation by heavy water, standard values for heavy water reactors, and economical use of the volume of the vessel, this reactor is estimated to be capable of operating in excess of 1,000 megawatts-thermal. It is important to note that this estimate remains uncertain, absent any confirmatory information from Pakistan.

Based on the apparent rate of construction, the reactor could be finished within a few years. However, nothing suggests that Pakistan is moving quickly to finish this reactor.

“The driving forces behind the reactor completion schedule could be a shortage of necessary reactor components or other parts of the weapons-production infrastructure such as the rate of heavy water production, the availability of a sufficient fuel reprocessing capacity or, perhaps, the availability of sufficient modern tritium recovery and packaging facilities,” the report says.

“For example, Pakistan may not have enough heavy water for this reactor, which could require about 100-150 tons of heavy water,” the report adds.

According to the report, the Khushab site has a heavy water production plant able to produce an estimated 13 tons of heavy water a year, a relatively small production capability. Pakistan may not be able to reprocess all of the anticipated irradiated fuel from this reactor.

Pakistan is known to process fuel to separate plutonium at the New Labs facility at Rawalpindi, and this facility was expanded between about 1998 and 2002. However, this increase in capacity was believed to be associated with the smaller, heavy water reactor.

The institute believes that India is already aware of this reactor construction in Khushab.

Neither Pakistan nor India have signed the nuclear Non-Proliferation Treaty, and both are believed to have substantial quantities of weapons.

India is reported to have 69 Prithvi and Agni ballistic missiles — each with one warhead — plus many more bombs that can be dropped by bombers.

Pakistan is thought to have 165 missiles of various versions of its Hatf series of missiles — each with a warhead — plus bombs capable of being dropped by air.

But experts say that because Pakistan uses a simpler uranium-based warhead design — as opposed to the more sophisticated plutonium version used by India — Islamabad is eager to upgrade its arsenal.