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PARIS, May 3 (Reuters) - Irregularities have been found in around 50 Areva-made components installed in French nuclear reactors, nuclear regulator ASN said on Tuesday.

It said that after the discovery of weak spots in the reactor vessel of the EPR reactor under construction in Flamanville, France last year, Areva began a review of manufacturing procedures at its Creusot steel forging plant.

In a statement, ASN said it had been informed by Areva that its investigation had found evidence of irregularities in about 400 components produced since 1965, of which some 50 are believed to be in use in French nuclear plants.

It made no comment about some of these components being in use in Areva-built nuclear plants abroad.

The ASN said it has asked Areva to provide as soon as possible a list of the relevant components and its analysis of the possible impact on security in France’s nuclear plants, in cooperation with their operators.

French utility EDF operates 58 nuclear reactors in 19 nuclear plants in France, which produce about 75 percent of the nation’s electricity.

“The review will have to assess how serious these anomalies are and what the consequences are for the safety of the installations,” the ASN statement said.

On Monday, Areva said some reports on manufacturing and quality control at Creusot - which supplies the nuclear market with large forgings and castings - may have been falsified.

Areva shares closed 7.4 percent lower on Tuesday. They have lost 47 percent of their value over the past 12 months.

Areva’s reactor business is expected to be taken over by EDF in 2017 and the company will receive a government rescue package after years of losses wiped out its equity.

The manufacturing problems further dented the reputation of Areva, whose flagship EPR reactor has suffered years of delays and billions of euros of cost overruns at construction sites in France and Finland.

EDF and its Chinese partner CGN plan to build two EPRs at Hinkley Point, Britain.