The 440 MW Kakrapar plant (pictured) in Gujarat, which came online in 1995 and is operated by the Nuclear Power Corporation of India Ltd (NPCIL), was taken offline in March 2016 on order of India’s nuclear regulator, the Atomic Energy Regulatory Board (AERB).
The leaking, which was said to be widespread, was caused by a mysterious nodular corrosion, resulting in blistering which visually resembles the smallpox virus.
The resemblance led to a number of reports this month in the Indian and foreign press stating that the plant had actually ‘contracted smallpox’, with some reports referring to the corrosion as a ‘disease’ and a ‘virus outbreak’. In the UK, a popular newspaper ran the story together with a report on how the smallpox virus was eradicated in the 1970s, but “it is feared terrorists may have got supplies from Russia in the 1980s”.
At the time of the shutdown, the corrosion had spread throughout critical pipes in both of the plant’s 220 MW pressurized heavy water reactors (PHWR). No definitive conclusion has been offered as to its cause.
Investigators last year found four large cracks in a coolant tube, and subsequently discovered more cracking and leaking throughout the network of 306 zirconium-niobium alloy tubes, with some leaks dating back to 2012.
However, no corrosion has been found on similar coolant tubes used in other Indian reactors, including those manufactured in the same batch.
Detailed failure analysis on the affected pipes is still underway at the Bhabha Atomic Research Centre in Mumbai. According to the AERB, the corrosion could indicate the presence of a trace impurity in the carbon dioxide gas used in the annulus gas system of the coolant channels.
“Detailed investigations in this regard indicate that this could have happened sometime after 2012,” the agency added.