The Nuclear Power Corporation of India has ordered a probe into what it believes to be sabotage, after about 50 workers at its Kaiga plant in western India were exposed to radiation. The workers became ill on 24 November after drinking from a water cooler later found to be contaminated with tritium – a radioactive isotope of hydrogen.

The Kaiga plant employs heavy water as a moderator and the used heavy water – which will contain some tritium generated as a by-product of neutron bombardment – is stored inside the plant for eventual tritium recovery.

Atomic Energy Commission chairman Anil Kakodkar says some of this tritium containing heavy water was possibly introduced into the cooler in a “malevolent act” by a disgruntled employee. All of India’s nuclear plants tightened their security after 16 November on being alerted by Washington on possible terror attacks.