According to scientists associated with Shakti '98, the tests demonstrated the Indian nuclear establishment's "mastery" over a range of nuclear weapon technologies and delivery systems.
THE message sent out to the world when India conducted five underground tests at Pokhran on May 11 and 13 was that India had become a full-fledged nuclear weapon state.
"The process of weaponisation," A.P.J. Abdul Kalam, Scientific Adviser to the Defence Minister, told newspersons in Delhi on May 17, "is complete." He was addressing a joint press conference with Dr. R. Chidambaram, Chairman, Atomic Energy Commission, and Secretary, Department of Atomic Energy. Also present at the press conference were Dr. Anil Kakodkar, Director, Bhabha Atomic Research Centre (BARC), and Dr. K. Santhanam, a senior scientist of the Defence Research and Development Organisation (DRDO).
Among other things, Kalam observed: "When nuclear technology and defence technology meet, they gets transformed into nuclear weapons technology. This is what the nation witnessed on May 11 and 13." Considerations of national security were an important factor in the decision to undertake the nuclear tests, he added.
According to Kalam and Chidambaram, the DRDO and the DAE had "effectively and efficiently" coordinated and integrated their technological strengths in "a national mission to confer the country with a capability to vacate nuclear threats."
The five tests were carried out under a secret project codenamed Shakti '98. The preparations for the tests were finalised within 30 days after the Bharatiya Janata Party-led Government gave the go-ahead. On May 11, three tests were conducted - with a fission device, a low-yield device and a thermonuclear device (better known as a "hydrogen bomb"). The fission device was similar to the one tested on May 18, 1974 at Pokhran but had a new design. It was smaller in size and weight but its yield was higher - 15 kilotonnes, compared with 12 kilotonnes in 1974. On May 13, two tests were conducted with two sub-kilotonne devices.
Kalam, who is the father of India's Integrated Guided Missile Development Programme, said that India had delivery systems that could carry nuclear warheads. A joint statement by Chidambaram and Kalam said that the tests "provided critical data for the validation of our capability in the design of our nuclear weapons of different yields for different applications and different delivery systems." In other words, both the intermediate-range surface-to-surface missile Agni and the short-range surface-to-surface missile Prithvi could deliver nuclear warheads - or, as Kalam noted, "flowers", if that was what was required of them.
Chidambaram pointed out that the fissile material used in the five tests was completely indigenous and that this confirmed the DAE establishments' "mastery" over the relevant technologies. But he declined to disclose details of the fissile material used or the depth at which the tests were conducted.
According to Chidambaram, the fission device had a yield of 15 kilotonnes, the low-yield device 0.2 kilotonnes and the thermonuclear device 45 kilotonnes. The yields from the two sub-kilotonne devices exploded on May 13 ranged between 0.2 and 0.6 kilotonnes.
(If the yield of a nuclear test is one kilotonne, it means that the energy of that nuclear explosion is equivalent to an explosion of 1,000 tonnes of trinitrotoluene, or TNT. A sub-kilotonne device gives a yield of less than 1,000 tonnes of TNT.)
The shafts were a kilometre apart from each other. The devices were exploded simultaneously so as to ensure that the explosion of a device in one shaft did not damage the other. The proximity of Keotalai village, about 5 km from the test site, was another constraint. The yield had to be contained to the lowest optimum level, Chidambaram said. A video film of the explosions showed that the three nuclear devices exploded simultaneously at 3.45 p.m. on May 11: the cameras used to film the event were jolted by the shockwaves.
Chidambaram praised the "excellent synergy" between the DAE and the DRDO. The Indian Army and the Indian Air Force (IAF) also made major back-up contributions. The Army helped prepare the site, dig the tunnel and build the shafts. Air Force helicopters flew over the site soon after the explosions to detect whether there was any release of radioactivity into the atmosphere.
The tests confirmed that India is a nuclear weapon state; they also provided scientists and engineers with voluminous data to conduct computer simulation of subcritical experiments of "zero yield". This was the aim of the two sub-kilotonne tests of May 13. The Comprehensive Test Ban Treaty does not prohibit zero-yield tests; the U.S. has conducted several subcritical tests. In any case, India is not a signatory to the CTBT.
BARC, the premier laboratory of the DAE, designed and developed the devices and fabricated the fissile material used in them. Kakodkar said that BARC scientists developed software packages that simulated underground tests. According to Kakodkar, the measured yields from the explosions agreed with the expected design values.
Responding to claims by Western nuclear experts that the thermonuclear device tested was not a hydrogen bomb but "a boosted fission device", Chidambaram confirmed that it was indeed a hydrogen bomb, a secondary fusion devise with a fusion trigger. (Authoritative sources said that a boosted fission device would have been easier to design, but scientists had opted for the two-stage device, which was more difficult to design, for the thermonuclear test.)
The joint statement by Kalam and Chidambaram gave details of the coordinated efforts of the DAE (including BARC), the DRDO, the Army and the Air Force. BARC designed and developed various kinds of nuclear explosives, including thermonuclear and low-yield devices. It engineered new concepts such as long shelf-life of device components. BARC scientists and engineers optimised the yield-to-weight ratio. They fabricated fissile materials of suitable shapes.
The DRDO's expertise in explosives, systems engineering and systems integration was put to use. One of the laboratories of the DRDO "weaponised" the proven design. This involved the design, test and production of advanced detonators, high-voltage trigger systems, interface engineering, systems engineering and systems integration to military specifications. Three other laboratories contributed to aerodynamics, arming, fusing, safety interlocks, flight trials and so on. The DRDO also conducted a series of trials and achieved the necessary operations clearances.
The DAE and the DRDO also thanked the Army and the IAF for their assistance in helping prepare for the test in various ways. The statement by Chidambaram and Kalam also recorded their "gratitude to the current Government, as well those in the past, for reposing confidence in the ability of the DAE and the DRDO to meet nuclear threats."
INFORMED sources said that the plutonium for the tests came from the Cirus and Dhruva research reactors at Trombay and was reprocessed at the Trombay Reprocessing Plant. The low-yield device that was detonated on May 11 used enriched uranium, which came from the Rare Metals Plant, near Mysore, the sources said. In the thermonuclear device, the triggering could have been done either by uranium or plutonium. One scientist said: "If reports that some of these explosions used Uranium 235 for fission are true, India has evidently reached a high level capability in uranium enrichment of more than 90 to 95 per cent. This is a great technological achievement."
The scientist summed up the significance of the five tests thus: "We have complete mastery over a range of nuclear weapon technologies and they are intended for different delivery systems. Also, we can do computer simulation of subcritical experiments in the future."
In other words, a short-range missile like Prithvi and a long-range intermediate missile like Agni could be equipped with nuclear warheads. The low-yield device was "a tactical weapon" which could be used as a battlefield missile for "localised effect" when two armies were locked in confrontation. A nuclear engineer added: "The low-yield device is a small weapon that can be mounted on a small missile and can be aimed at specific targets." Another scientist noted: "The-low yield tests were done to send a message that we can control the yield to any level."
In a hydrogen bomb, the fission process generates heat of up to "thousands and thousands of degrees Celsius," which triggers a fusion process akin to the "creation of the sun". When hydrogen gets fused, massive quantities of energy are released, setting off shock waves and heat waves that can annihilate everything in the surrounding areas.
The expert sources said that the first test with a fission device was a "repeat" of the 1974 experiment, and it was mainly intended to re-establish what was done in 1974. But the latest fission device had "an advanced design" and was lighter.
Why is not plutonium from power reactors, such as those at Kalpakkam in Tamil Nadu or Narora in Uttar Pradesh, used in nuclear explosive devices? A scientist explained that when the fuel - uranium - in a power reactor undergoes irradiation, Plutonium 239, which is a byproduct, converts itself into higher isotopes of plutonium such as Plutonium 240 or 241, which are not easily fissionable. "So what we need is a higher concentration of Plutonium 239, which can be got by low irradiation of fuel in a research reactor." But this does not mean that nuclear explosive devices cannot use plutonium from power reactors.
ONCE the Centre gave the go-ahead, the Bhabha Atomic Research Centre (BARC), Trombay, got down to work. Various groups from the BARC belonging to disciplines such as physics, engineering, electronics, instrumentation and control designed and devised the devices. While the DAE team was led by Chidambaram, the DRDO was led by Abdul Kalam, who also interfaced with the Army. Kakodkar played a major role in the tests.
Since the DAE was not authorised to handle chemical explosives (that go into the "core" of the devices), the DRDO fabricated them. But the designing of the chemical explosives, particularly for the thermonuclear device, proved to be complicated; complex computer software was used in the design process. The DAE busied itself with designing, engineering, fabricating and detonating the devices through remote control.
The three tests on May 11 were conducted "simultaneously, with automatic electrical firing." Only milliseconds separated one explosion from another. The sub-kilotonne tests of May 13 were also simultaneous. The explosions left five craters in the Rajasthan desert.
According to a nuclear engineer, sufficient care was taken to ensure that radioactive elements were not released into the atmosphere. The implosion was engineered in such a manner that the sand kicked up fell back into the crater created. "So radioactivity is not released into the atmosphere," he explained. He, however, said that residential dwellings in the neighbourhood of the Pokhran military range had developed cracks.
DAE sources said that they themselves were surprised that the U.S., with its advanced military reconnaissance satellites, could not spot the preparations for the test in the desert. "This was especially so because so much work was going on towards the end of the week." The U.S. had also failed to detect the 1974 test.
The Western nations slipped up on another front as well. A network of seismic stations operated by them interpreted the shock waves generated by the explosions as "an earthquake on the Indo-Pakistan border." One informed source said: "The International Data Centre (IDC) analyses data with the help of a global seismic network, consisting of 45 stations. The IDC is supposed to be part of the CTBT verification system. They interpreted the shock waves from the May 11 test as an earthquake on the Indo-Pakistan border." Seismic wave forms, the sources said, were very complex and it was not easy to interpret them because explosives were detonated simultaneously.
Today, there is immense pride and jubilation among nuclear scientists and engineers on a mission successfully accomplished.
