LONDON - France's Caisse D'Amortissement de la Dette Sociale (CADES) has set the final size of a planned increase of an existing bond maturing in 2012 at 1.5 billion euros ($2.1 billion), IFR reported on Thursday.

Guidance has been fixed at mid-swaps plus 9 basis points, slightly tighter than the initial 10 basis points area talk, said IFR Markets, a Thomson Reuters online news and market analysis service.

CADES, the agency in charge of refinancing the country's social security debt, is rated triple-A. ($1=.7165 euros)

(Reporting by Natalie Harrison; editing by Mike Nesbit)