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MUMBAI, Mar 19 (PTI): In a highly guarded Indian nuclear reactor complex, toughened radiation resistant pipes have contracted ‘small pox’. As a consequence, literally in a plot similar to a Bollywood thriller Indian scientists are burning the midnight oil to unravel the mysterious nuclear leak at the Kakrapar Nuclear Power Plant in Gujarat. This 21st century atomic pot boiler is actually unfolding through the hard work of scientists, who actually share a wall with the famous property where renowned Bollywood film star Raj Kapoor used to live.
Here, they are working over-time to find out the real cause of the cryptic leaks at twin reactors in southern Gujarat. To avoid any panic and any further accidents, the Indian nuclear watchdog – the Atomic Energy Regulatory Board (AERB) – has shut down the affected plants till the cause has been found. Nuclear experts say pipes, made from a rare alloy, have contracted what seems like ‘small pox’ and this contagion has spread all over the critical tubes in two Indian Pressurised Heavy Water Reactors (PHWR) at Kakrapar in Gujarat.And, to make the matters worse, after more than a year into the investigation, the teams of scientists really do not understand what has gone wrong.
It was on the morning of March 11, 2016, and as fate would have it exactly five years after the Fukushima reactors in Japan started exploding, unit number 1 of the 220-MW PHWR at Kakrapar developed a heavy water leak and had to be shut down in an emergency.
The indigenously built nuclear plant suffered a heavy water leak in its primary coolant channel and a plant emergency was declared at the site. No worker was exposed and no radiation leaked outside the plant, confirmed India’s Department of Atomic Energy. India’s nuclear operator, Nuclear Power Corporation of India Limited (NPCIL) said “reactor had shut down safely” and “no radiation leaked out”. It confirmed that safety systems had functioned normally.
The atomic thriller really begins when experts are trying to find out why a leak recognition system failed, in the first place it should have given an alarm. “There is a leak detection system in place in all PHWRs, but in this case it failed to detect the leak on March 11, 2016,” confirms AERB Chairman S A Bhardwaj. AERB speculates that the crack developed so rapidly that the electronic leak detection system just did not had the time to react. Subsequent investigations revealed that the leak detection system was fully functioning and the operator had “NOT shut it down” to cut costs.
Nothing in the core of a nuclear reactor can be done in a jiffy and several weeks after the first leak, initial probe using a specially designed tool revealed that four big cracks had formed on a coolant tube which led to the massive leak.
The discovery of the crack was only the beginning of the mystery, further efforts to find the root cause established that the outside of the tube, the part which was not exposed to high temperature heavy water, was also for some unexplained reason “corroded”.
This was a stunning discovery, since the outside of the failed tube was exposed only to high temperature carbon dioxide and there had been no recorded case of a similar corrosion having been seen on the outside of any tube. It is also very hard to access this part since the space was very tiny in the annulus.
The AERB then ordered that all the tubes made out of a special alloy of zirconium-niobium be checked on the outside, to their surprise, they discovered that the contagion of the “nodular corrosion” or what in layman’s language can also be described as “small pox-like” was very widespread in many of the 306 tubes. Tubes made from the same batch and used at other Indian reactors continue to operate faithfully, without corrosion. The needle of suspicion now pointed to the carbon dioxide, a gas known to be very stable in high radiation environments.
A further post mortem revealed that the Unit-2 which is twin of the affected reactor had also been affected by a similar leak on July 1, 2015 almost ten months before the Unit 1 had a sudden appalling failure in March 2016. Investigations into why the Unit-2 failed were ongoing but no conclusive result had been found. This literally back-to-back failure of two fully functional nuclear reactors befuddled the engineers.
Unrelenting in trying to find out the root cause, the AERB ordered that entire assembly and not just the affected tube be safely pulled out and brought to India’s foremost nuclear laboratory, the Bhabha Atomic Research Center (BARC) in Mumbai for detailed failure analysis. It is this laboratory located at Trombay in Chembur, in Mumbai that shares geography with India’s famous Bollywood Kapoor family. In addition, since India operates another 16 similar nuclear plants, a full-fledged investigation was carried out on the coolant channels of all atomic power plants and lo-and-behold the investigating team found that the “small pox” like corrosion was confined only to the two units that operated at Kakrapar.
While this gave a sigh of relief to the NPCIL but it increased the complexity on trying to unravel the true cause of the leaks at Kakrapar. Today, Bhardwaj says the investigators are wondering if the carbon dioxide used in Kakrapar may have been contaminated which caused the “nodular corrosion” on the outside of the pipes.
The source of the carbon dioxide was further back traced and it seems only the Kakrapar plant was sourcing its gas from a “Naptha cracking unit” and possibly it has some contamination of hydrocarbons. No conclusive evidence on the contamination has been forthcoming and forensic analysis is still under way.
As it turns out nuclear engineers are masters of book-keeping especially when ageing of equipment is concerned and a more detailed check in the history of the plants revealed that in 2012 two tubes had been extracted from the Kakrapar plant as part of routine maintenance and had been safely stored in a safe warehouse. When these were re-examined in 2017, the investigators were surprised that the “small pox” like corrosion on the exterior of the tube was not present.
This now makes the investigators suspect that something went wrong after 2012. Meanwhile, the AERB and the atomic energy establishment has also reached out to the vast global nuclear community to try and help resolve this mystery.
The global watchdog the International Atomic Energy Agency in Vienna and ten other global forums have been informed that a mysterious leak is dogging the Indian reactors at Kakrapar and if the global community could be of some help. The international community is as much at a loss in explaining the failures as are the Indian teams. India operates 18 PHWR reactors and over the years it has accumulated some 348 years of operating experience of these unique nuclear plants powered using natural uranium and in all these years, the Department of Atomic Energy asserts no radiation related death has taken place at any nuclear plant and no radiation has ever leaked out of the Indian PHWR’s.
In addition to it, 29 PHWRs are today functional in Canada, Argentina, Romania, China, South Korea and Pakistan and none have reported any issue like the ‘small pox like corrosion’ on any of its nuclear plants.
Bharadwaj says right now there are only hunches but teams at BARC are exposing the Zircalloy tubes to carbon dioxide spiked with various contaminants and they are being placed in a high radiation environment to accentuate the aging process to try and determine the exact cause of the two processes—“small pox like nodular corrosion and the development of cracks in the coolant tubes.” These could be linked or independent, says Bhardwaj, who feels that in the next few months, the root cause will definitely be deciphered till then the reactors will remain shut.
India currently operates 22 nuclear reactors with an installed capacity of 6,780 MW and hopes to ramp up nuclear output to 32,000 MW by 2032. Meanwhile, the continuing nuclear mystery is giving the vast Indian nuclear establishment and its atomic sleuths ‘nuclear jitters’.
By – Pallava Bagla
Comments by Prof. Anil Gupta
a) non-uniform alloy itself, that is if alloy has been made in batches , then some batches may have had slight difference leading to patches like distortion; b) using an analogy of with disease in chickpea, where the fungus exists among roots of healthy plants also but disease manifest only in patches, probably because of changing c/n or c/p ( carbon phosph or nitrogen) ratio in those patches; the root cause may be more widely prevalent but problem may come in patches, c) is it possible that surface physics has to explain the problem.