An internal investigation is on by a team of nuclear experts in Kaiga in Karnataka, after at least 50 people working in the nuclear power plant were treated for excessive radiation exposure after drinking water mixed with tritium, a highly radioactive substance.<br/><br/>The team in Kaiga is probing last week's incident in which 45-50 employees working in the first maintenance unit of the plant were treated for increasing level of tritium, also known as Hydrogen-3, after they drank water from a water cooler in the operating area on last Tuesday.<br/><br/>The affected workers have since returned to work. Security at the plant has since been beefed up.<br/><br/>The Government and Atomic officials have said that all workers at the state-run plant are safe and there is no scare of a radiation leak in the area.<br/><br/>A criminal investigation has been launched after the Atomic Energy Commission said radioactive tritium used in nuclear reactors was deliberately put in a water cooler.<br/><br/>Atomic Energy Commission Chairman Anil Kakodkar said people involved will be punished. <br/><br/>NPCIL Chairman and Managing Director S K Jain said, preliminary enquiry does not reveal any violation of operating procedures or radioactivity releases or security breach and it is possibly an act of mischief.<br/><br/>Minister of State for Atomic Energy Prithviraj Chavan said it has to be seen whether it was an act of a disgruntled individual.<br/><br/>The Government says prima facie some insider is involved in the Kaiga nuclear plant incident in which around 50 workers of the power plant have been found to have been exposed to radiation.<br/><br/> <br/>Talking to reporters outside Parliament, Minister of State for Science and Technology Mr Prithviraj Chavan, said that only people having biometric pass have access to the area where from some water was taken out and put into the water cooler. He said the investigation is in advanced stage and expressed hope that it will be concluded soon. <br/><br/>The Prime Minister, Dr Manmohan Singh while returning from Port of Spain allayed fears of nuclear accident and said there is no reason to worry.