Wales coach Warren Gatland will have access to his Grand Slam winners for 13 days before their opener against Scotland at Murrayfield on 8 February after achieving player access he wanted for the RBS 6 Nations.
The major boost to Wales' hopes of retaining the Six Nations title comes after an agreement between the Welsh Rugby Union and the Welsh regions.
Wales also have first call on the players for the entire competition, even though there are two weekends of regional matches during the tournament.
The regions agreed to the terms after meetings at the start of this week.
After losing their Under-20s Six Nations crown to England Under-20s in a thrilling final round, France Under-20s lock Tristan Labouteley insists his side will be out for revenge at this year's Junior World Championship.