The 25-year-old Agen scrum-half was named up in the squad last week to replace Dimitri Yachvili on the bench, the latter promoted to the starting line-up after charismatic captain Fabien Galthie injured his right shoulder in France's 38-3 victory over Scotland on February 23.
"I was really not expecting it," Barrau said. "I thought they (Laporte and team manager Jo Maso) would chose someone else with more experience than me.
"This is like a dream coming true but on the other hand I know it could be a short-lived one. But if I have to play, I will be ready for it.
"I have only been called up, and I will have to work hard if I want to keep my hopes of staying alive."