The father of the dud thermonuclear bomb Dr R Chidambaram is on record describing how a real atomic explosion works. This description is recounted in Raj Chengappa’s engrossing book Weapons of Peace: The Secret Story of India’s Quest to be a Nuclear Power (Harper Collins, 2000) which provides a broad-brush overview of the development of both India’s nuclear and missile programmes. The author obviously had access to all the main players, the laboratories, which kind of makes it an almost official narrative. Chengappa who interviewed Chidambaram on June 10, 1998, writes (page 187): “Chidambaram’s eyes always light up when he describes what happens when an atom bomb is exploded deep underground. He says that under the intense heat of over a million degrees centigrade (emphasis mine) a mini-mountain of rock vaporises underground. And an equal amount melts… Meanwhile the shock waves of the blast strike the surface and cause a mini-mountain of sand to rise from the ground. The mound formed is called a retarc, the word crater spelt backwards. As the force of the explosion weakens in intensity the mound collapses inwards forming a giant crater.”
What basically happens is that the explosion vaporises material around it and then the vapours expand rapidly and push outwards in all directions creating shock waves that crushes more rock. “At the ‘Taj Mahal’ site (S1 where the fission device, weaponised for delivery through a missile exploded) the shockwaves from the blast lifted a giant mound of sand (page 430), the size of a hockey field (emphasis mine). DRDO’s colonel Umang Kapur who was flying high above in a helicopter to monitor the radioactivity and video film the event saw a plume of dust. As he neared he saw that the bunkers around the side had toppled like a pack of cards. Then, in awe, he watched a giant crater form as the sand poured down through a cylindrical chimney to fill up the cavity deep below the ground. …. On the ground the scientists suddenly felt the earth under their feet quake violently…. (They) ran out in time to see a giant wall of sand akin to a tidal wave rise and fall.”
At the White House site (S2 where the dud thermonuclear device was placed), if we are to go by what the scientists led Chengappa to believe, it was placed at a depth of 200 metres (page 427) in contrast to S1 which was about 50 metres less deep (at “over 150 metres”, page 422). This dud device was rated at 45 kt yield, three times the yield of the fission device in Taj Mahal shaft and was buried about 50 metres deeper, in a shaft a kilometre away. There is, however, good reason to believe that the shafts were not as deep as this since they had been in existence since 1981 and going by the accounts in the book were not deepened when readied for the 1998 tests; scientists familiar with the work say that the deeper shaft did not go as deep as 200 metres. A yield of one kiloton is the explosive energy equivalent of a thousand tons of TNT. The bomb that US dropped on Hiroshima was 15 kilotons, only a third of the explosive energy the dud thermonuclear bomb allegedly set off.
At the bottom of the second shaft, a kilometre away, was the thermonuclear weapon. It had a fission-based trigger. The second stage was the fusion weapon. The shaft ran more than a 120 metres into the ground. At the bottom it veered slightly to the left, making an ‘L’. After the turn it ran for a further five metres, called an adit. The small tunnel was about six feet high, high enough for a person to stand. The width was about three metres. To get the men and materials into the shaft there was a winch that was suspended from an A Frame run by a diesel motor. The entire shaft was cased and shielded by a thin steel casing of .3 mm. This was to prevent or reduce seepage from subterranean streams that could mess up the wiring, among other things. Both S1 and S2 were old shafts, dug in 1981 when Rammana was adviser to defence minister. But they had been wired up from 1995 when Narasimha Rao was weighing the option of conducting nuclear tests. The three-year-old wiring had been in good working condition and the test team did not have to relay the cables, both for giving the command and for instrumentation, which was the responsibility of the DRDO, and not the BARC. For the 1998 tests, the shafts weren’t deepened or modified further.
The Control Room was about 2.5 km from ground zero. It was a tin shed with air conditioning and had all the instruments both for command cables and cables for instrumentation and recording. It was manned by working scientists and engineers of DRDO; the engineers were directly involved in instrumentation and recording process. Instrumentation within Pokhran was 100 per cent DRDO. Aviation Research Centre seismic instruments were outside Pokhran. The DAE had instrumentation in the shaft for Cortex which was a prototype. (It later transpired that the prototype Cortex failed to work). There were television cameras looking at ground zero, accelerometers, ground motion sensors, and a central recording place where the data stream was slipped. Instrumentation in 1998 was of a much higher order than 1974. This is undisputed.
After the explosion once the helicopter indicated there was no radioactivity in the air, the two teams Bravo (scientists from Bombay) and Delta (those from DRDO) went to inspect their work. According to Raj Chengappa, “The Taj Mahal site had a giant newly formed crater. But the Hydrogen bomb site wasn’t as impressive. A mound of several metres had risen and the sheds all around it had collapsed in a crazy heap. Some of the scientists looked worried. There was concern whether the secondary fusion device had properly detonated… That afternoon, however, Chidambaram and Sikka were confident. They told the rest that because the shaft was a very deep one and located on granite strata the impact on the surface was minimal. Reassured, the team headed back to break the news to the Prime Minister in Delhi.” (pages 431-432). The reconstruction of the final Pokhran moments in the book is based on author’s interviews with Chidambaram, S K Sikka, Anil Kakodkar, K Santhanam and Abdul Kalam.
According to one source who visited the site immediately after the test, apparently Chidambaram and the Bravo team stared in silent disbelief at the failure of the experiment. The blast had failed to even dislodge the winch and the A frame which stood in mute eloquent testimony to the failure. In the distance the scientists could see the yawning hole of the shaft grin mockingly at them. It had been a Gandhi bomb, totally non-violent.
(Tomorrow: Kalam and the Gandhi Bomb)
sudarshan@epmltd.com
About the author:
V Sudarshan is the Executive Editor of ‘The New Indian Express’