UPDATE 1-French nuclear regulator to rule in 2020-21 on EDF reactor lifespan

* First ASN recommendation expected in 2020

ASN in contact with EDF on safety of spent fuel pools

* EDF and Areva have investigated half of Creusot documents (Adds details, quotes, background)

PARIS, Nov 8 (Reuters) - France's ASN nuclear regulator will rule on a potential lifespan extension of EDF's nuclear reactors in 2020-21, ASN chief Pierre-Franck Chevet said on Wednesday.

France's 58 nuclear reactors, operated by state-controlled utility EDF, were built in large part between the end of the 1970s and early 1980s and are coming to the end of their 40-year lifespan, which EDF wants to extend to 50 years.

"We estimate that we will issue a first recommendation in 2020, which will be followed by a legally binding ruling in 2021," Chevet told a parliamentary committee.

In a hearing on the safety and security of France's 58 nuclear reactors, Chevet said safety levels were satisfactory overall, despite a number of anomalies and incidents that have been reported in recent weeks.

But he reiterated that the financial difficulties of utility EDF and reactor builder Areva were worrying from a safety point of view.

Chevet said that the standardisation of French nuclear stations - all reactors use the same pressurised water reactor technology and have been built by the same company - makes problem detection easier but also increases the risk of a major generic flaw that forces the closure of several reactors at the same time.

Responding to questions from Greenpeace about the safety of EDF's spent-fuel pools, Chevet said the ASN is in contact with EDF about how to improve the safety of the pools, which can contain two to three reactor cores but which do not have the same thick containment walls as the reactor vessels.

He said the absence of a "core catcher" in all of EDF's existing reactors will also be an issue in the ASN's decision to extend the lifespan or not.

EDF's new EPR reactor, under construction in Flamanville, has a core catcher that can contain the core in case of meltdown. Other reactors could suffer the "China Syndrome" with molten fuel burning into the ground and reaching the water table in case of an accident, Chevet said.

He also said that EDF and Areva had investigated about half of the millions of pages of manufacturing documentation at Areva's Creusot forge unit.

French regulators last year discovered manufacturing flaws and falsified documentation at the Creusot Forge, which makes components for nuclear reactors.

So far, two issues with potential impact have been found. However, Dominique Miniere, EDF's head of nuclear facilities, told the hearing that no major safety problem linked to the Creusot components investigation had been detected on a reactor.

"My message is that since the review is not yet closed we will no doubt in the coming year find one or two, a few bad surprises," ASN's Chevet told the hearing. (Reporting by Geert De Clercq and Bate Felix; Editing by Sudip Kar-Gupta, Brian Love and Adrian Croft)