Nuclear Power Corporation (NPCIL) is likely to focus on the reliability of back-up power systems at some of the operational nuclear stations as it looks to reinforce safety measures in the wake of the Japanese nuclear accident.

While the results of a safety audit conducted on existing plants are expected in the coming weeks, Government officials indicated that the emphasis is expected to be on strengthening the support infrastructure of the atomic plant that could prove vital in the event of a forced shutdown.

BACK-UP POWER SYSTEMS

Nuclear stations generally have several back-up diesel generators and battery-powered systems that supply power to motor-driven cooling systems, which will continue the supply of water or coolant to dissipate heat in the event of a forced shut-down. While during an earthquake, the reactor would be expected to automatically shut down (called a reactor scram), the reactor continues to produce heat equivalent to about 3-5 per cent of its full power level even after that. This drops off gradually and is why there needs to be layers of redundant cooling with back-up power. Especially in the event of a major earthquake, when power from outside the plant would not be expected to be available. The crippled Fukushima Dai-ichi nuclear power plant in Japan, which withstood the magnitude 9 earthquake, suffered severe damages to its diesel generators and back-up power systems in the tsunami that followed the quake.

REVIEW PROCESS

An NPCIL official explained that the review process is part of a well established operating experience review programme at the utility in which international events are reviewed for their applicability in the Indian context and corrective measures are taken.

“The events in Japan are being reviewed in detail in due course as the detailed information is being made available. Following the review, any reinforcement will be implemented,” an NPCIL official said. Officials said NPCIL and DAE are maintaining a close contact on the developments through the NPCIL authorised representative in WANO's Tokyo centre as also with International Atomic Energy Agency (IAEA) and other agencies.

SAFETY PARAMETERS REANALYSED

NPCIL currently operates 20 nuclear power reactors with an installed capacity of 4,780 MW. Of these reactors, two are Boiling Water Reactors of 160 MWe each at Tarapur while all others are Pressurised Heavy Water Reactors (PHWRs). The safety of these BWR units, which are of the same type as the six units of the Fukushima Dai-ichi station, were reanalysed few years ago and reviewed by Atomic Energy Regulatory Board (AERB), NPCIL officials said. Following this, the two BWRs at Tarapur have been renovated, upgraded and additional safety features back fitted to latest safety standards, an official said. The PHWRs are of different design than that of BWRs and have multiple, redundant and diverse shutdown systems as well as cooling water systems, they said.

The Indian plants have testified their safety towards the severe earthquakes of Gujarat in Bhuj on January 2001 when the Kakrapar Atomic Power Station continued to operate safely, supplying power to the region. Also, during the tsunami that hit the Tamil Nadu coast in 2004, Madras Atomic Power Station (MAPS) was safely shutdown without any radiological consequences and the plant was restarted in a matter of days after regulatory review. The Koodankulam under construction also remained unaffected by the tsunami as the higher level chosen for locating the plant

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