India increasing stock of weapons-grade plutonium
WASHINGTON: Since the 1998 nuclear tests, India is believed to have invested more resources into increasing its inventory of weapons-grade plutonium, the focus being the increase in the plutonium output of the Cirus and Dhruva reactors, according to a recent study.
David Albright of the Institute of Science and International Security (ISIS) writes that an estimate of India’s military plutonium stock is composed of two basic assessments. The first involves calculating the total amount of plutonium produced in the Cirus and Dhruva reactors. A part of this assessment is accounting for any plutonium from Candu power reactors assigned to the military program. The second assessment involves determining the amount of plutonium produced in these reactors that has been consumed or used for non-military purposes.
According to Albright, “It is assumed that almost all of the plutonium is successfully recovered during reprocessing. Any estimate of India’s weapon-grade plutonium inventory remains highly uncertain. Complicating any estimate is the mixture of solid and ambiguous information regarding India’s capabilities and actions. As a result, an analytical approach is used that specifically aims to capture varying and conflicting information about key parametres affecting estimates of the size of India’s plutonium stock.”
According to Albright, the formula used to estimate the total amount of weapon-grade plutonium produced in the Cirus or Dhruva reactors is straightforward. The most critical parameter in estimating the total amount of plutonium produced by one of these reactors is its capacity factor, which is defined as the energy produced divided by the amount theoretically possible to produce in a year. Estimates of the capacity factors of these reactors vary widely.
Indian officials state that the reactors achieved a capacity factor of 60 to 70 percent over long periods of time. Indian senior nuclear officials stated in interviews in 1992 that the annual capacity factor of the Dhruva reactor was 60-65 percent. Indian officials also state that Cirus achieved a capacity of 70 percent until 1990, after which the capacity factor decreased because of aging problems in the reactor. One report implied a capacity factor of less than 50 percent during this period.
Albright writes, “These statements cannot be confirmed and interpreting them is difficult. Dhruva had a capacity factor less than 25 percent during its first few years of operation. Other problems may have developed in the reactor that lowered its lifetime capacity factor below 60-65 percent. Indian officials may be giving capacity factors for periods when the reactors operated well and ignoring periods when the reactors were shut down or operating at significantly reduced power. This practice is rather common when discussing nuclear power reactors. In this case, a capacity factor of 60-65 percent would more likely be a maximum lifetime capacity factor.
Such an interpretation is supported by statements from US government experts. In the late 1990s, knowledgeable experts from US national laboratories stated in briefings and interviews that the Cirus and Dhruva reactors had achieved a lifetime capacity factor of only about 40 percent. These estimates were widely circulated at the time, but their reliability could not be ascertained.”
The ISIS expert, a former IAEA inspector, believes that the amount of plutonium from power reactors assigned to the military programme is believed to be relatively small. Some of the plutonium produced in the Cirus and Dhruva reactors has been used in nuclear tests, lost in processing, or assigned to civil fuel. These quantities must be subtracted to derive the net plutonium stock. The largest overall users of plutonium from these reactors have been civil reactors utilising plutonium fuels, including the Fast Breeder Test reactor (FBTR), the Purnima reactor, the Zerlina reactor, and power reactors. Nuclear testing in 1974 and 1998 also used a portion of this plutonium.
Albright writes that the net military inventory is the total amount of plutonium produced minus the amount of plutonium used in nuclear testing, lost during processing, and assigned to civil uses. At the end of 2004, the median value of the estimate of this inventory is 445 kilograms of plutonium, and the 5th and 95th percentiles are 360 and 530 kilograms, respectively. Estimates of the number of Indian nuclear weapons are highly uncertain.
Media and government sources continue to suggest that India has not built as many nuclear weapons as it could, given its inventory of weapon-grade plutonium. Nonetheless, India has likely used the bulk of its plutonium to make nuclear weapons. “As a result, an upper bound estimate of India’s nuclear arsenal at the end of 2004 can be derived from its estimated stock of weapon-grade plutonium. In this estimate, the amount of plutonium needed for a nuclear weapon is represented by a triangular distribution that varies from 4 to 7 kilograms with the most likely value as 5 kilograms. The median value is about 85 weapons, and the 5th and 95th percentiles are about 65 and 110 weapons, respectively.” khalid hassan