Dr K S Parthasarathy
The accident at Fukushima nuclear power plant shook the confidence of the public all over the world. Are Indian nuclear power plants safe?
India took the accident seriously. Soon after the accident, the Atomic Energy Regulatory Board (AERB) set up a committee to review the safety of Indian nuclear power plants against external events of natural origin and to make appropriate recommendations.
Nuclear Power Corporation of India Limited (NPCIL) set up six separate task forces depending on the differences in the safety features of its nuclear power plants. Boiling Water Reactors (BWR) at Tarapur Atomic Power Station (TAPS 1&2); Pressurized Heavy Water Reactors (PHWRs) at Rajasthan Atomic Power Station (RAPS 1 &2); PHWRs at Madras Atomic Power Station (MAPS 1&2); subsequently constructed standardized PHWRs from Narora Atomic Power Station onwards; Kudankulam reactors and PHWRs of 700 MWe capacity. . These committees revisited the adequacy of the safety features of India’s nuclear power plants:
The earthquake that hit Fukushima was very powerful at magnitude 9 in the Richter scale; the plants tripped on receiving the signals from the seismic sensors.
Earthquake did not damage the reactors. The devastating 15 metre high tsunami that followed it did. Tsunami snatched away all electric power sources. Even after the reactors were shut down coolant must flow uninterrupted to remove decay heat. As the coolant pumps failed due to loss of power, cores of three reactors melted releasing copious amounts of radioactive material later causing the serious accident.
NPCIL made fail proof provisions to cool the reactor cores of its nuclear power plants in case of total power loss.
Pressurized Heavy Water Reactors (PHWR) which form the backbone of the current Indian nuclear power programme have a notable safety feature. Their cores may be cooled during shut down state by flow of coolant by natural convection. If power fails totally, operators can add water using diesel engine- driven pumps to keep the core cool.
In 1993, the operators at Unit1 in Narora could successfully maintain reactor core cooling by using fire water system when fire knocked out all power sources; there was no power in the grid for 17 hrs.
NPCIL installed seismic trips in all reactors. They recalculated the possible flood levels at plants where there was such a possibility. For instance, they asked what if the upstream dams at Unit 2 of the Rajasthan Atomic Power Station break. They provided two additional emergency diesel generators (air cooled) at higher elevation for supplying essential power needs in case of such a flood.
NPCIL provided seismically qualified hook-up arrangements kept above possible flood level to add cooling water to various systems in case flood occurs; additional air compressor at higher elevation for supplying instrument air to critical valves and dampers and seismic strengthening of additional water storage tanks.
NPCIL reassessed the flood level at MAPS-1&2 and revised it from 8.9m to 12.9m. To take care of the impact of floods, NPCIL provided 200 kVA air cooled, Emergency Diesel Generators (EDGs) at higher elevation; flood protection measures for existing EDG and an additional uninterruptible power supply to feed power to vital instruments to monitor how the plant behaves if power is not available for long.
NPCIL provided seismically qualified hook-up arrangements to add cooling water if needed, to various systems including spent fuel pool in both units
Presently, all stations have additional backup diesel generators (air cooled mobile/ installed at higher elevation). NPCIL found the need for additional diesel driven pumps for specific purposes and additional mobile pumps and fire tenders and augmentation of onsite water storage to enhance safety. These measures are in progress.
NPCIL provided additional emergency lighting, backed up by solar cells in some stations. All reactors now have external hook up points to add water to steam generators and other systems which require cooling.
Some long term upgrades such as strengthening hydrogen management provisions; provision for venting of containment; creation of an On-site Emergency Support Centre capable of withstanding severe flood, cyclone & earthquake are in progress
At units 1&2 of Tarapur Atomic Power Station NPCIL provided enhanced flood protection measures for Station Black Out. If severe floods occur, diesel generators, and emergency core cooling pumps & valves kept at higher levels will be operable. NPCIL has provided alternate routes through multiple points to inject water in to the Reactor Pressure Vessel. There is alternate provision to replenish water in spent fuel pool inside the reactor building and Away From Reactor (AFR) storage facility. NPCIL is taking steps to implement nitrogen inerting of primary containment at TAPS 1&2.
On May 6, 2013 while disposing of the PIL against Kudankulam Nuclear Power Plant, the Supreme Court thus cautioned the authorities:
“The AERB as the regulatory authority and the MoEF are obliged to perform their duty that safety measures are adequately taken before the plant commences its operation. That is the trust of the people in the authorities which they can ill afford to betray, and it shall not be an exaggeration to state that safety in a case of this nature in any one’s hand has to be placed on the pedestal of “Constitutional Trust”.
Over the past four decades, AERB accumulated experience and expertise to fulfill its mandate.
Indian nuclear power plants are safe because Indian safety specialists have, in light of Fukushima accident, implemented additional measures to enhance their safety status.
(The author is a former Secretary of the Atomic Energy Regulatory Board. He can be contacted at ksparth@gmail.com.)
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