By Geert De Clercq
PARIS (Reuters) - EDF is employing new techniques in a bid to restart four nuclear reactors that have been idled for months due to a series of glitches, a top executive at the French utility said.
EDF had to close two of the reactors following the discovery of manufacturing problems and document falsification at the foundry of its supplier Areva, while the others were shut down by a sealing problem and an accident.
The outages have led to higher power prices, are undermining France's security of supply and are costing EDF an average of one million euros in lost revenue per reactor per day, or nearly 1.5 billion euros ($1.6 billion) on an annual basis.
Philippe Sasseigne, the head of EDF's 58 French nuclear power stations, said it had found several new technical fixes and that all four plants would restart this year if its proposals get the go-ahead from French nuclear regulator the Autorite de Surete Nucleaire (ASN).
"We are confident that we will get approval to restart the four plants on the scheduled dates," Sasseigne told Reuters in a telephone interview. The restart schedule, published by grid operator RTE, runs between June and November.
One of EDF's most pressing problems is the closure of Areva's Creusot Forge, which is under investigation by the ASN and is not expected to restart production before the summer.
Creusot Forge is EDF's main supplier of steam generators, which turn a reactor's heat into the steam that drives its power turbines. Each EDF reactors is cooled by three to four steam generators and every year EDF needs to replace one or two.
The huge steel vessels - which have life spans of 30 years or more - have thousands of individual tubes inside them which gradually develop leaks and need to be blocked.
In October, an Areva-made steam generator set to be installed in EDF's Gravelines 5 reactor in northern France was found to contain serious anomalies. It is scheduled to restart on June 30.
Sasseigne said the ASN last month allowed EDF to fix any leaks in the tubes by inserting new, smaller tubes in a process called "sleeving". This is already practiced in the U.S., Sweden and Belgium and can extend the life of the part by two years.
EDF has no plans to use the procedure on other plants, although it could do so if necessary, Sasseigne said.
While sleeving could be an important fallback if Creusot Forge does not restart in time, EDF could also turn to others such as Toshiba-owned Westinghouse or Mitsubishi Heavy Industries for its steam generators.
The Fessenheim 2 reactor in northeastern France has also been halted since June after Areva discovered that one of its steam generators had higher-than-expected carbon concentrations, which could weaken its steel.
EDF is not planning to repair or replace that steam generator, but hopes to convince the ASN that Fessenheim 2 can operate safely.
The utility sent a first dossier to the ASN last year, but the regulator asked for more information, forcing EDF to delay the planned restart. EDF will send the ASN more data by the end of April and hopes to restart the reactor by July 31.
Sasseigne said EDF was now also close to finding a solution for sealing problems at its Bugey 5 reactor in eastern France which has been closed since August 2015 as EDF has been unable to find a tiny leak in the reactor building's steel inner lining.
EDF planned to redo the sealing of the entire lower part of the lining, Sasseigne said, adding that it expects to get the ASN's approval for the repair in within days or weeks.
Other 900 MW reactors tested for sealing issues had shown no problems, he said.
The last reactor expected to return to service is Paluel 2 in northwestern France, where a steam generator was dropped on the floor of the reactor building last year.
Checks have shown this had no impact on the building's integrity and EDF expects the reactor to restart on Nov. 30, Sasseigne said.
This steam generator was removed from the building in January, and EDF now needs to take out another, fix the reactor pool and install new steam generators, which have already been delivered.
However, before EDF can install the new generators, it needs to get ASN approval to overhaul the plant's lifting system.
"There is still some way to go, but as of today we are confident we can stick to that deadline," he said.
($1 = 0.9408 euros)
(Editing by Adrian Croft and Alexander Smith)