50-Metre Crater At Test Site

A 50-metre-deep crater lies at the Pokhran test site where three nuclear devices were tested on Monday.

The explosions, in short succession of one another, released 30-50 kilotonnes of energy at a depth of 110 metres. Upon detonation at 3.15 pm, the ground rose rapidly, causing a dome that collapsed after few seconds, resulting in the crater. The radioactivity was contained within the soil, prompting Prime Minister Atal Behari Vajpayee to assert that the measured yields are in line with expected values.

Given the intensity of the blast, all rock formations within 5 metres of the epicentre must have been vaporised; two metres beyond, they must have melted, a nuclear expert said. The 1974 Pokhran test, with an intensity of 12 kilotonnes, vaporised some 640 tonnes of rock and melted another 2,000 tonnes. The destruction in Mondays blasts is substantially greater. Extensive computer modelling preceded the tests because exploding a thermonuclear device underground is a bold decision to take in terms of containing the explosion and the subsequent radioactivity. The Atomic Energy Commission (AEC) has its own supercomputer, PaceSparc, developed specially to meet the computing needs of the nuclear industry.

The AEC started preparations during March-April because the nature of the tests requires meticulous planning. Especially the low-yield device, a controlled explosion for short-range weapons that needs very sophisticated technology and complete mastery over the nuclear cycle.

The AEC used a computer program called One-dimensional Spherical Symmetric Rock Mechanics Code that simulates the physio-chemical processes in the rock medium on sudden release of energy.

The values are obtained through geo-sensors placed at strategic locations around the blast site. The program, run on a supercomputer, most probably the PaceSparc, gives out post-explosion values.

The 1974 blast had shaken the earth in a 40-metre radius at a depth of 10 metres after the ground rose at a velocity of 25 metres per second, reaching a height of 170 metres before collapsing.

The plutonium used as the base of the explosive devices came from the Bhabha Atomic Research Centre at Trombay that had also supplied plutonium for the 1974 test. Spent fuel from nuclear power plants is reprocessed at the Trombay plant for extracting weapons-grade plutonium.