The Karachi Nuclear Power Plant in Pakistan declared a seven-hour emergency after a heavy water leak from a feeder pipe.
The leakage at the plant, known as KANUPP, started during a routine maintenance shut down but no radiation or damage has been reported, said plant spokesman Tariq Rashid.
The 137-megawatt power plant, which started commercial operations in 1972, is located about 24 km to the west of Karachi, Pakistan's biggest city and commercial capital, on the Arabian Sea coast.
"The plant was already shut down since Oct. 5 and the leakage started during maintenance checks," Rashid said.
He said the emergency was imposed at the plant immediately after the leak and the affected area was isolated.
The emergency was lifted seven hours later, after the leak was brought under control.
"The situation is completely under control and no damage or radiation has been reported, though it will slightly delay the reopening of the plant," Rashid said, adding that the plant will be operational again in 4-5 weeks.
KANUPP supplies 80 megawatts of power to the Karachi Electric Supply Co, the city's main power utility.
The plant completed its 30-year design life in 2002 and underwent upgrades to extend operations.
"Currently it is well designed to work till at least 2015," said Rashid.
Karachi's peak power demand is up to 2,500 megawatts.
Pakistan has two commercial nuclear complexes, with the second located at Chashma in the Punjab province.
Nuclear power accounts for only about two per cent of total power supplies.
China, which helped build the Chasma complex, plans to help Pakistan expand there by building two more reactors in addition to the two already operating there.
Safety is a major concern in Pakistan's existing and future nuclear power plants, which analysts say are derived from designs dating back to the 1970s.