Any damage to fuel bundles could have resulted in thousands of times more severe radiation leakage from the reactor, and some of it could have eventually escaped into the public domain, say experts.
The recent leak in coolant channels of the Unit-1 reactor at the Kakrapar Atomic Power Station near Surat in Gujarat is a warning which necessitates thorough investigation of all such reactors in the country, say experts.
At 9 am on March 11, a leakage in the Primary Heat Transfer system led to the reactor being shut down and a plant emergency declared at KAPS. It has two units of pressurised heavy water reactors of 220 mw each; Nuclear Power Corporation of India is the operator.
According to site officials, one of the channels carrying the fuel bundles and the heavy water coolant had leaked. The high-grade radioactivity from the fuel itself was confined within the fuel bundles and no radioactive substances escaped from the reactor containment building.
The Atomic Energy Regulatory Board has stated that, as of now, KAPS' Unit-1 is in a shutdown state, even as all plant systems are 'functioning normally.'
Those worried say Kakrapar was lucky to have witnessed leakage of heavy and light water from the coolant channel without any serious damage to fuel bundles in the reactor.
"As against (the March 2011 disaster at) Fukushima (in Japan), in the case of Kakrapar, the channel saw only leakage of heavy water and the fuel bundles do not appear to have overheated or melted," former AERB chairman A Gopalakrishnan said.
"The heavy water coolant, which has been circulating in the reactor for a long time, would have reached a certain level of radioactivity, due to neutron absorption. Luck favoured Kakrapar as only a very small amount of radioactivity seems to have escaped during the brief venting of the containment," he added.
Any damage to fuel bundles could have resulted in thousands of times more severe radiation leakage from the reactor, and some of it could have eventually escaped into the public domain, he said.
Seconding him is nuclear activist and physicist Surendra Gadekar, monitoring the Indian nuclear industry since 1987.
"The problem has been isolated, but the fact is it took them 10 days to do that, with the plant emergency ending on March 22. They claim it is a 'small leak,' which otherwise does not call for a plant emergency for 10 days. They were lucky that they didn't find any radiation in a 20-km radius," says Gadekar.
What took everyone by surprise is that, while the reactor itself is 24 years old, the pressure tubes of the coolant channels were replaced in 2011 with new ones from an improved zirconium-niobium alloy, supposed to be resistant to such cracking.
"How could a coolant channel meant to function well for a conservative 25 years incur a leakage in only five years?" asks Gadekar.
Apparently, KAPS' health physics unit, the Bhabha Atomic Research Centre's Environmental Survey Lab and a team from BARC Ahmedabad and Tarapur have been conducting regular radiation surveys in a 20-km radius of the plant, apart from the reactor building perimeter wall, plant premises and in the public domain that stretches up to a 5 km radius from the plant boundary. So far, the surveys have not found any radiation.
"Unless they check all reactors in the country, they will not be able to ascertain whether it is a local or a generic problem. It might be a local problem," Gadekar adds.
There are 21 nuclear power plants in the country, with a capacity to generate a combined 5,780 mw of power.
Dr Gopalakrishnan says while such an investigation of all the 17 such reactors of the Pressurised Heavy Water Reactor type might be needed, it should be done after first ascertaining the nature and cause of the KAPS leakage.
"The hard task is to find why it happened and then consider avenues for in situ inspections and subsequent repairs. Area monitoring of air and water in the vicinity must be continued at regular intervals. All the NPCIL and contract workers alike must be monitored for the cumulative radiation dosage they are receiving until the current leakage issue is put to rest. They need to first get to the bottom of what happened at Kakrapar," he said.
The AERB has maintained that the leak has been isolated with the plant emergency being terminated.
'There has not been any report of abnormal radioactivity releases/radiation exposures to any personnel during this incident, since March 11. With the leak completely stopped, investigations for identifying the nature of the leak and its causes can now be taken up. However, it is expected that this could take considerable time,' it has stated.
The state government, too, has been monitoring the situation, with the administration of Tapi and Surat districts asked to stay on standby and ensure workers' and residents' safety, said Govind Patel, minister of state for energy.
According to site officials, around 300 workers with special radiation safety suits have been working on the clean-up.
'We are systematically proceeding for early assessment of the location and nature of leak. Once this is detected, root cause analysis will be conducted to find out the exact cause of the incidence. All applicable procedures and guidelines are being followed,' the NPCIL had recently stated.
