PARIS, Jan 12 (Reuters) - Shares in French utility EDF sank to all-time lows on Tuesday after the country's Andra nuclear waste agency said that storage costs could be higher than EDF's estimates.
Mirroring German utilities E.ON and RWE , which saw their shares hit decade lows late last year over worries about nuclear decommissioning costs, EDF fell as much as 7.3 percent before recovering to 4.1 percent lower.
A string of brokerage price target downgrades and French forward power prices falling to new decade lows only added to the gloom.
In a report released late on Monday, Andra said costs for the Cigeo deep geological storage project could be as high as 30 billion euros or as low as 20 billion depending on assumptions about different cost factors in coming years.
"There are different views on the calculation, more or less conservative, depending on estimates for future technological progress and optimisation," Andra said in a statement.
In a letter to the energy ministry, posted on the ministry's website, EDF, fellow state-controlled company Areva and the CEA (Atomic Energy Authority) said they estimated the cost at around 20 billion euros.
"Andra's study only took into account a small number of possible optimisations," said the letter, adding that a certain number of costs and ratios used by the state agency were not in line with their experience.
"We are waiting for a decision of the energy minister on the cost of storage," an EDF spokesman said.
Energy Minister Segolene Royal's decision on the 10 billion euro gap in estimates could have a huge impact on the already stretched balance sheet of EDF, which operates 58 nuclear plants in France and generates the bulk of the country's nuclear waste.
EDF already needs to borrow money just to pay its dividend and is set to spend tens of billions of euros on upgrading its ageing reactors, building new nuclear plants in Hinkley Point, Britain and buying the reactor arm of Areva.
"This report is clearly negative for all nuclear operators, and most specifically for EDF and Areva," Bryan, Garnier analyst Xavier Caroen said in a note, adding that the risk of a cost revaluation was not new.
EDF shares are down more than 44 percent in the 12 months, the second-worst performer in the Stoxx utilities index after RWE. The company has been replaced in France's CAC-40 index of leading shares by shopping centre operator Klepierre . (Additional reporting by Benjamin Mallet; Editing by Keith Weir)