Nuclear Reactors 269 - Strange Corrosion Found At Indian Kakrapar Atomic Power Station
There are two Indian two hundred and twenty watt Pressurized Heavy Water Reactors (PHWR) at the Kakrapar Atomic Power Station near the city of Vyara in Gujarat State in India. KAPS-1 went online in 1993 and KAPS-2 went online in 1995.
A year ago, KAPS-1 developed a leak of heavy water coolant. An automatic leak detection system failed to detect the leak and both reactors were shut down manually. India's Department of Atomic Energy (DAE) said that no one was exposed to radiation and no radiation leaked out of the plant.
Later an investigation of the incident but the operators could find no fault in the automatic leak detection system. There were some news stories that claimed that the operators of the plant had shut down the leak detection system to save money but these charges proved to be unfounded.
Further investigation found that four large cracks had developed on a coolant pipe which caused the leak. The investigators also found that a " nodular corrosion contagion" of pockmarks reminiscent of smallpox scars had spread over all the coolant pipes in both of the reactors. The pipes are made of a rare zirconium-niobium alloy. They are hard to access for examination.
Some of the pipes are exposed to high-temperature heavy water while other pipes are only exposed high-pressure carbon dioxide. The origin of the corrosion is unique and has not been found in the pipes of other Indian reactors of similar construction. At this point, it is suspected that the corrosion is connected somehow to the carbon dioxide which has been very stable in high radiation environments.
Close examination of the KAPS-2 reactor showed that it had experienced a similar heavy water leak ten months before the KAPS-1 leak. The piping for both reactors was disassembled and shipped to the Bhabha Atomic Research Center (BARC) in Mumbai for detailed failure analysis. As part of their investigation. The BARC examined the piping for sixteen other Indian nuclear power reactors with the same PHWR design as the KAPS reactors. The results of that investigation found that the only reactors where the smallpox-like corrosion developed were the KAPS reactors.
During routine maintenance on the KAPS in 2012, two pipes from the cooling system had been removed from the plant and stored in a warehouse. BARC investigators went to the warehouse to check the old pipes. Interestingly, the two pipes from 2012 showed no sign of the nodular corrosion now present at the KAPS.
Mystified by the development of the corrosion at the KAPS, BARC has reached out to other members of the international nuclear power industry for help. The International Atomic Energy Agency and ten other global forums for nuclear power have been contacted about the developments at KAPS. Twenty-nine PHWRs are operating in Canada, Argentina, Romania, China, South Korea and Pakistan and none of them show any signs of the corrosion found at KAPS. So far, the international contacts have no answers.
The BARC investigators are experimenting with tubes of the zirconium-niobium alloy in high-pressure carbon dioxide and high radiation environments. KAPS obtains their carbon dioxide from a "Naptha cracking unit" and it may be possible that the carbon dioxide was contaminated with hydrocarbons. The BARC investigators are adding different contaminants to carbon dioxide in the hope that they will find a combination of carbon dioxide and contaminants that will cause corrosion similar to what has been found at KAPS.
