Last year's Six Nations and World Rugby Junior Championship winners scored four tries to pick up a bonus-point win as they triumphed 32-10. With six of last year's World Cup winners, and 10 players boasting Under 20 experience, the French were packed with talent.
But Reffell and fellow back row man Taine Basham led by example and, after surviving an explosive start from the home side at Stade de la Rabine, Wales actually led midway through the first period.
Home outside half Louis Carbonel, the top scorer at last year's World Cup, kicked an early penalty, but Wales responded with a brilliant try from replacement centre Joe Roberts, who came on after only four minutes when Tom Hoppe took a head knock in a tackle.
A solid scrum gave Wales the chance to attack for the first time and after first moving the ball to the right, they pulled it back to the left and a great pass from Cai Evans gave Roberts to pin back his ears and outflank hooker Rayne Barka to score from 25 metres.
Evans added the conversion and also went on to kick a 40-metre penalty. The French response saw them edge into 17-10 interval lead thanks to tries from flanker Sacha Zegueur and wing Matthis Lebel, both of which Carbonel converted.
The Lebel try came on the stroke of half-time and the French followed that up with a third try eight minutes after the re-start when giant lock Killian Geraci barged over. Carbonel added a penalty 10 minutes later, but they had to wait until the final move of the game before securing the bonus-point when right wing Vincent Pinto was sent racing 40 metres up the right touchline to score a try that Carbonel improved.
The French had to play the final few minutes without Zegueur. Zegueur received a red card from Scottish referee Ben Blain for his part in a double tackle on Wales replacement hooker Will Griffiths that saw the ball carrier hoisted in the air and dumped on his neck.
France: Tries: Zegueur, Lebel, Geraci, Pinto Conversions: Carbonel (3) Penalties: Carbonel (2)
Wales: Try: Roberts Penalty: Evans Conversion: Evans