The head of France's nuclear safety authority, Andre-Claude Lacoste, this week warned that EDF would have to modernize most of its reactors to have their lifetime extended.
Such a modernization, Lacoste told the Financial Times, "without doubt would require massive investment."
EDF, which is 85 percent owned by the French government, runs 58 nuclear reactors in France that satisfy around 80 percent of the domestic power demand.
In the United States, most of the nuclear reactors have had their licenses extended to 60 years but French authorities are considered more strict.
EDF has estimated that it would cost around $550 million to modernize one reactor, an investment that would pay off in the long run: Most of the existing plants have already amortized and their extension by two decades could add value of an estimated $1.6 billion, the Financial Times writes. The radical option is much more expensive: Replacing an old plant with a new one would cost $5 billion-$6 billion.
The French nuclear safety watchdog won't go easy on EDF, however.
The agency has already forced EDF to promise to replace aging steam generators on 34 of its 58 reactors, Lacoste said. The retrofitting is expected to cost several hundred million dollars and is necessary after the agency had observed age-related malfunctions related to the generators.
EDF this month reported a net income of $5.3 billion for the financial year. Most of the income was generated by its power business in Britain, where the French bought nuclear power operator British Energy. But the multi-billion-dollar purchase almost doubled EDF's debt, currently amounting to around $50 billion.
EDF is expected to lead Britain's nuclear energy revival -- it has announced it would build four nuclear power plants at different locations. It also aims to build reactors in the United States, China and Italy.
But to unlock further investment options, EDF's new Chief Executive Officer Henri Proglio will have to oversee several asset sales over the next years to reduce the utility's debt.
EDF had planned to raise $5 billion-$6 billion with the sale of its British grid but is now reportedly mulling to keep it.