UPDATE: A HD Clip is now available. The film comes out on DVD/Bluray on January 14.
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UPDATE: The movie is out today. It sounds like her nudity is very brief, as her left breast is briefly visible from the side while showering.
There is also a scene with four women in bed together, one showing full-frontal.
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UPDATE:The IMDB poster gave a little bit more additional information.
"It's a side shot, but you see her full chest."
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There was a public screening of the upcoming film "Riddick" this past Thursday. The IMDB message poster who announced the screening and watched the film had this to say about nudity from Katee Sackhoff in the film.
"She gets fully topless, but it's a relatively quick glimpse".
http://www.imdb.com/title/tt1411250/board/thread/218508347?d=218525189#218525189
Only one source, but the screening he announced beforehand did happen and he has given other details about the film. Riddick premieres in theaters on September 6.