Nuclear officials are trying to calm fears about a possible radiation leak after an accident at an atomic plant in Karnataka.

They say there was no radioactive leak, and most people affected are safe and the environment around the plant unaffected. But what's more worrying is that an insider hand is suspected in what is being seen as a case of sabotage.

Some workers fell ill after drinking water from a cooler that was contaminated with tritium, a radioactive form of hydrogen. The cooler was located within the secure premises of reactors 1 and 2.

Alarmed authorities have ruled out a security lapse, but blame an employee, who is yet to be caught or identified.

"No breach in security by outside person. Have clear cut records of who has entered. It's a cause of serious concern, and a mischief by an insider," says Dr S K Jain, CMD, Nuclear Power Corporation of India Ltd.

The contamination was detected during a routine check on the workers for radiation exposure. The urine samples of four employees had high levels of tritium, but within permissible limits. Authorities insist all are safe.

It seems a small quantity of heavy water, which is used for testing, was pilfered, either from a lab or a reactor, and added to the water cooler. Authorities were quick to explain what happened, largely to put at rest a greater fear about a radioactive spill.

"I want to assure everyone that this process of making electricity from a nuclear power plant has no problem and there is no leakage accident either," says Minister of Science and Technology Prithviraj Chavan.

This radiation exposure at Kaiga is being viewed as a serious procedural lapse and a criminal investigation will most likely identify the culprit.