Coolant channel source of Kakrapar water

This story has been updated to include information released by the AERB on 16 March. 

A coolant channel assembly has been identified as the source of a leak of heavy water coolant at Kakrapar unit 1, India's Atomic Energy Regulatory Board (AERB) has confirmed. The unit remains in a cold shutdown state following the 11 March incident.

The coolant leak caused the reactor to automatically shut down at about 9.00am on 11 March, after which a plant emergency was declared at the 202 MWe indigenously designed pressurized heavy water reactor (PHWR). The reactor is being continuously cooled, and the AERB said that at present, there are no major safety concerns.

The AERB said that there had been "no radioactivity releases exceeding the specified daily limits for normal operation" and also that no workers had received abnormal radiation doses. Independent environmental monitoring carried out up to 20 km from the plant has found no increase in background radiation levels or radioactive contamination, the AERB said, "corroborating that no abnormal releases have taken place."

The AERB said on 16 March that the leaking coolant channel had been identified. "A small part of the cooling water is continuing to leak out of the coolant system, and is being replenished through [the] recirculation system," the regulator said.

A detailed plan for isolating the leak has been drawn up by operator Nuclear Power Corporation of India Ltd (NPCIL). The AERB has reviewed the plan and given permission for it to be implemented, after which investigations into the nature of the leak and what caused can begin. "However, it is expected that these investigations could take considerable time. The plant has been asked to remain in the safe shutdown state till the investigations and the corrective actions are completed," the AERB said.

Kakrapar Atomic Power Station - sometimes referred to as KAPS - is home to two 202 MWe PHWRs, operated by NPCIL. Two 700 MWe PHWRs - also indigenously designed - are under construction at the site. Kakrapar 1 began commercial operation in 1993 and underwent a major refurbishment, including replacement of coolant channel pressure tubes, between 2008 and 2011. Kakrapar 2 has been off line since July 2015, the AERB said.

The pressure tubes in a PHWR form channels to hold the reactor fuel, which is cooled by a flow of heavy water under high pressure in the primary cooling circuit. The primary coolant generates steam in a secondary circuit to drive the electricity-generating turbines.

Researched and written
by World Nuclear News