Two workers at the Rawatbhata Atomic Power Station in Rajasthan have suffered exposure to high doses of radioactive tritium and are under observation.
The incident took place on June 23 at Unit 5 of the plant during routine maintenance work.
"There was no abnormal release of radioactivity to the environment," Nalinish Nagaich, Executive Director, Nuclear Power Corporation of India Limited said from Mumbai.
He said there was localised increase in tritium concentration in the building of Reactor-5 due to the opening of the moderator cover gas line where the welding jobs were to be performed.
"All persons involved in the maintenance work were monitored and two were found to have four to five times higher uptake of tritium," Nagaich said.
The exposure of other persons is below the annual exposure limit specified, he said.
The incident was reported to the Atomic Energy Regulatory Board (AERB) and was investigated by independent committees set up by the regulator and NPCIL. Tritium is a mildly radioactive type of hydrogen that is formed in the operation of nuclear power plants.
The workers had inhaled it while carrying out maintenance activities in the reactor building and it will come out of the body on its own through urine. The level of tritium in the body is expected to reduce appreciably within a week.
The NPCIL, in a report on its website, said that the incident occurred when a modification work for assuring a provision of alternate water addition to the moderator system in the Reactor-5 was being carried out.
"The uptake occurred due to inadvertent rise in tritium levels in a localized area of the containment building of the Reactor-5," it said. In 2009, a large number of workers at Kaiga atomic plant had taken ill after consuming tritium-laced water from a water-cooler.