According to an industry source, the unit is expected to generate around 720 MW early next week.
"We have given permission for NPCIL Friday evening to increase the power generation levels at its first unit in Kudankulam beyond 50 percent and up to 75 percent," S.S. Bajaj, the Atomic Energy Regulatory Board (AERB) chairman, said over phone from Mumbai.
Bajaj said the unit would conduct tests. Based on the reports, further increase of power generation would be permitted.
"If all test results are satisfactory, then we may give permission to increase power generation levels up to 100 percent," Bajaj added.
The NPCIL is setting up two 1,000 MW Russian reactors at Kudankulam in Tirunelveli district, 650 km from here. The total outlay for the Kudankulam Nuclear Power Project (KNPP) is over Rs.17,000 crore.
KNPP site director R.S. Sundar said: "We are now operating the plant at 570 MW levels. We will hold at this level for some more time."
Queried about touching the 75 percent reactor power levels early next week, he said: "We may go up to that level by Tuesday or Wednesday."
Sundar said the unit had to get two more permissions before it can go up to 100 percent reactor power levels.
"The first stage of permission will be to go beyond 75 percent and up to 90 percent. The second stage will be to go up to 100 percent from 90 percent power levels," Sundar said.
KNPP is India's first pressurised water reactor belonging to the light water reactor category.
The first unit attained criticality in July 2013, which is the beginning of the fission process.
In August 2013, AERB permitted NPCIL to operate the reactor up to 50 percent level.
As the first unit at KNPP is yet to be declared commercially operational, the power generated is termed as infirm power and supplied to the home state - Tamil Nadu - at low rates.
"Currently, the power is supplied to Tamil Nadu power utility at just over Re.1 per unit," said a source not wanting to be identified.
Only when the unit is declared commercially operational, NPCIL can charge higher rates. NPCIL is expected to realise a commercial tariff of around Rs.2.60 per unit.
"Now Tamil Nadu is enjoying the benefits of cheap Kudankulam power. Once the unit is declared commercially operational, it will start supplying power to other southern states as well," the source said.
According to Sundar, the decision on declaring the unit as commercially operational rests with the officials in the corporate office in Mumbai.
A senior NPCIL official said last week that the focus was on increasing the reactor's power levels to 75 percent and stabilise the operations.
The NPCIL on its web site has declared that the first unit at KNPP would become commercially operational next month.