Anil Kakodkar

Nov. 29: A “mischief-maker” added heavy water to a water cooler at the Kaiga nuclear power plant in Karnataka, exposing 50-odd workers to radiation overdoses and sparking fears of a radiation leak, India’s atomic energy authorities said today.

They added that there was no leak, no worker needed to be hospitalised, and that only two now had “marginally” higher-than-specified levels of the radioactive tritium.

They will be all right with treatment and the rest have gone back to work since Tuesday’s incident, a media release by the Atomic Energy Regulatory Board (AERB) said.

Treating the matter “very seriously”, the junior minister for atomic energy, Prithviraj Chavan, said an inquiry was on into the “malevolent act” to find out if it was a “disgruntled” employee acting alone.

B. Bhattacharjee, a member of the National Disaster Management Authority, said AERB investigators believed it was an inside job but would try to find out if the culprit had been put up to it by “some outside pressure”.

The incident “has not in any way affected public safety, health or environment”, said J.P. Gupta, Kaiga station director.

“The preliminary inquiry does not reveal any violation of operating procedures or radioactivity releases or security breach. It is possibly an act of mischief,” said S.K. Jain, chairman and managing director of the Nuclear Power Corporation (NPC), which operates India’s commercial nuclear power reactors.

A routine urine examination of some workers on Tuesday had revealed their exposure to tritium, a type of hydrogen atom produced when heavy water — used as a coolant in India’s indigenous nuclear reactors — absorbs neutrons.

The source was then identified — a water cooler outside the reactor building that has now been “isolated and put out of service”, Jain said.

“The water tanker of this cooler, like all other water coolers, was kept locked. However, it appears that some mischief-maker added a small quantity of tritiated heavy water to the cooler, possibly from a heavy water sampling vial, through the overflow tube,” the AERB release said.

All those who had drunk from the cooler were sent to the plant hospital where they were given diuretics to flush out the tritium from their bodies.

Only two now have a tritium level that could cause their annual exposure to radiation (as part of their work) to marginally exceed the AERB-specified limit of 30 milli-sievert (mSv), the release said.

But treatment will bring the level below this limit “in a short time”, the release said, adding that the limit prescribed by the International Commission on Radiation Protection was much higher — 50mSV a year.

Jain, however, said only one worker had a higher-than-specified level of tritium.

Atomic Energy Commission chairman Anil Kakodkar said: “No harm is expected as there is plenty of margin between the permissible exposure level and exposure level when it causes some harm.”

Heavy water looks and tastes just the same as ordinary drinking water, but contains different types of hydrogen atoms — either a deuterium atom with an extra neutron, or a tritium atom with two extra neutrons.

Water containing tritium mixes with body water after its entry, but the human body is able to flush out the tritium through urination and sweating. Several scientific studies, though, have pointed to the potential toxicity of tritium.

The heavy water used in nuclear reactors passes through dedicated channels and containment systems and should not have been in any position to leak into the drinking water cooler.

Kakodkar said the guilty would be punished under the Atomic Energy Act and other laws.

“We are awaiting the completion of an internal inquiry because it is a technical subject and they have the expertise,” said Gopal Hosur, inspector-general of police (Western Range). The plant is located at Mallapur, some 40km east of Karwar town, in the Western Ghats.

One of the three operating units at Kaiga has been shut for annual maintenance since October 20, and Hosur said the contamination took place at that unit. The second and third units are operating normally, the NPC said.