All nuclear reactors at the site are safe. There are six units, of which Unit I has been shut for long. At present, four reactors are operating and Unit V is under start-up after completion of a planned biennial shutdown.
N Nagaich, executive director, said an incident of tritium uptake had happened in Unit-IV when under planned biennial shutdown.
The Investigation Level of the tritium uptake is defined conservatively at about 1/10 th of the authorised annual limit specified by the regulatory body. There was absolutely no release of radiation into the environment. The workers are continuing to perform their normal duties, albeit in other areas of the station, Nagaich said.
According to Nagaich, all the persons involved in the work were monitored as a regular practice. Only two persons are likely to exceed the annual exposure limits specified by the regulatory body.
The exposure of other persons is below the annual exposure limit specified. They have been assigned the work in non- radioactive areas as per the prevailing procedure applicable in such cases.
The incident was immediately reported to Atomic Energy Regulatory Board (AERB). The incident has been investigated by the committee deputed by NPCIL and by AERB independently. The appropriate measures as suggested by these committees to prevent such incidents in future, will be implemented promptly.
The incident occurred when a modification work, as planned during the shutdown, for assuring a provision of alternate water addition to the moderator system in the reactor -5 was being carried out. The uptake occurred due to inadvertent rise in tritium levels in a localized area of the containment building of the reactor -5. The localized increase in the Tritium concentration occurred due to the opening of the moderator cover gas line where the welding jobs were to be performed. Tritium, a heavier isotope is formed from heavy water during operation of the plant. Small quantities of Tritium exist in the form of vapour in the reactor building.
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