Nuclear Power Corpn to beef up safety standards

The Nuclear Power Corporation of India said the four task forces formed to revisit the safety aspects of nuclear plants in India, consequent to the happenings at Fukushima in Japan, have recommended the initiation of automatic reactor shutdown on sensing seismic activity.

Outlining the recommendations made by the task forces, Dr S. K. Jain, Chairman and Managing Director, NPCIL, said the recommendations include increasing the passive power source capacity for monitoring and control purposes, for longer durations; provision for hook-up arrangements for adding cooling water inventory through external sources to all reactor cooling systems and mobile, diesel-driven pumping units.

It has also been suggested that, if required, steps should be taken to augment water inventory and arrangements made for transfer of water from nearby sources.

The task forces also wanted additional shore protection measures to be undertaken at the Madras Atomic Power Station and the Tarapur Atomic Power Station, which are located on the coastline.

Dr Jain said though studies have indicated capabilities exist to handle severe natural events, the committees had come up with their recommendations to enhance the safety levels and build further depth in defence.

Close monitoring

NPCIL is closely monitoring the unfolding events at Fukushima and is getting information from international agencies such as the International Atomic Energy Agency (IAEA); the World Association of Nuclear Operators; the Japan Atomic Industrial Forum (JAIF); and from the NPCIL representative posted at the WANO Tokyo Centre.

He said the task forces, based on information available from the Fukushima reactor incident, had studied the capability of the reactors in India to handle identical extended loss-of-power scenarios.

The Indian nuclear power plants include two boiling water reactors and 18 pressurised heavy water reactors with three types of designs.

Their study indicated that unlike in Fukushima, the TAPS 1&2 reactors are provided with a completely passive means of core cooling in the form of an emergency condenser that does not require any motive power and caters to core cooling for a period of six hours. There are provisions to augment the water inventory in this condenser.

The TAPS 1&2 boiling water reactors began operations in 1969. On completing 35 years of operation, a thorough review was made of the performance and health of the equipment. The plants were modernised between 2004 and 2006. Additionally, it has been recommended that nitrogen be used to inert the primary containment, besides establishing an advance alert mechanism for tsunamis.

Seismic capability

Overall, the seismic capability of the structures has been found adequate for the seismic zone in which they are located. A tsunami on this coast can only be generated at the Makran fault near Karachi, which is 900 km away. The plant is found to be safe for the maximum height of tsunami that can be generated at the Makran fault. Additional shore protection measures were also being undertaken to absorb considerable energy from the tsunami waves.

The existing water sources at the site in the form of an emergency condenser, suppression pool and underground storage tank were adequate to cater to cooling requirements for extended periods of over 10 days.

As regards the first PHWR reactors at RAPS 1&2, the possibility of flooding from the upstream Gandhi Sagar dam was considered and on-site power has been ensured. A separate Station Blackout Diesel generator is also provided at a height of about three metres above the flood level. The water resources available at a higher elevation were adequate for the safety systems.

Additional safety

In the case of the Madras Atomic Power Station, the finished floor levels of the buildings were higher than the maximum flood level postulated. The station had withstood the Indian Ocean tsunami in December 2004 without any interruption in operations. Additional safety measures in the form of tsunami bunds had been constructed along the shore and a tsunami alert system is also available there. One diesel generator and two diesel-driven fire-fighting pumps are also located at a height of about three metres from flood level. The reservoirs on site are at a higher elevation. The water tanks and suppression pool would cater to the requirements for over 10 days.

At all the standardised PHWR reactors from Narora onwards, the seismic design is adequate to withstand seismic events that can occur in the seismic zone in which the plants are located. There is also a margin of one to four metres above flood level postulated for the sites. The water stored at these sites would be sufficient to meet requirements for more than 10 days and, in some cases, up to 30 days. The spent fuel pool water inventory has also been assessed to be adequate for more than 10 days.

The specialist committee constituted by the Atomic Energy Regulatory Board (AERB) would also be submitting its report and NPCIL would incorporate all its recommendations. The recommendations of the task forces would also be implemented immediately with AERB's approvals.

Mr Jain said the events at Fukushima were still unfolding. As and when more details became available, the recommendations would be revisited and additional measures that were deemed fit would be incorporated, he said.