TORONTO - In the French-language film "Partir," Kristin Scott Thomas plays a well-to-do wife who abruptly leaves her family to pursue a white-hot sexual affair with a working class Spaniard.

Thomas, 49, bares all in the movie, which is screening at the Toronto International Film Festival.

The Oscar-nominated actress says she thinks it's important to show sexual relationships between older characters, but wonders if American audiences might be "grossed out" by the movie's themes.

"This woman is doing everything wrong and loving it," Thomas said of the film, which has yet to find North American distribution.

"She's dumping her kids, she's leaving home comforts, she's going into a horrible, smelly ghetto place. She's sleeping with a man who's inferior socially. ... She's losing her mind."

She's also having sex. And plenty of it.

Thomas -- whose English-language film credits include "The English Patient" and "Gosford Park" -- said she relished the chance to take on such a sensual character.

"I think it's important to make films about women of my generation who are living life to the fullest, who are not sitting back and thinking wistfully about their lost youth or their lost beauty," said Thomas.

"You get to a certain age and you're supposed to be funny or to play a grandmother and it's just boring. I enjoy being funny in films, but I don't want to do just that. ... I love the idea of this middle-aged, passionate (woman). ... She just loses her mind over somebody. And I think that's great -- to be able to follow your instincts so strongly and live in the moment."

It's the second year in a row that the U.K.-born Thomas has been at the festival with a French-language film (she's lived in Paris since she was 19).

Last year, she wowed Toronto audiences with her performance as a newly released prison inmate in "I've Loved You So Long" ("Il y a longtemps que je t'aime").

Now, she's earning praise for her turn in "Partir" (the film has already been released in France, where Thomas says it's been "massively successful").

While she'll continue to alternate between French and English projects, Thomas says she likes the sensibility of movie-making in her adopted country.

In "Partir," director Catherine Corsini doesn't shy away from putting Thomas's middle-aged body on full display in the torrid scenes with her lover Ivan, played by Sergi Lopez.

"I think it's easier to identify, for a woman my age, with a scene like that rather than a scene where you have some beautifully carved and inflated body being filmed in sections so that you can't tell when the body double is moving in," said Thomas.

"I think that what's great about French cinema is they're more interested in the scars and the signs of experience than something ... that doesn't really have any feeling to it. It doesn't really have any proof of life."

Adds the actress: "We all live longer. This whole chasing youth business is just (ridiculous). If only people would just wake up and accept the fact that life just gets better and better and better."