Sources privy to the investigation said on Tuesday that the contamination incident, described as an “internal sabotage,” had links to the department from where moderator heavy water is supplied to the nuclear reactor.

The laboratory examination of the water from the cooler showed only the presence of tritium—a radioactive isotope of Hydrogen—and no other chemical.
Tritium is used along with other chemicals in a type of heavy water used to moderate the reactor’s high temperature.

According to sources, things were normal on November 23, but radiation effects in some employees were noted only on November 24 night.
The sampling of the moderate heavy water is done everyday whereas for coolant it is done once a week. Following this, a chart was prepared about the employees who had access to the moderate heavy water, out of which five people are being subjected to sustained questioning to unravel the mystery.

A team is probing the incident in which around 50 employees working in the first maintenance unit of the plant were tested for increasing level of tritium after they drank water from the cooler in the operating area on November 24.