The term "radical feminist" does not refer to a women who thinks women are superior to men. That would be a Female Supremacist.
A radical feminist is someone who believes that changes on a legal level are not enough to achieve true gender equality, and that in order for people to live without the oppressive nature of a gender heirarchy, we must undertake a mission of cultural change as well.
I am a radical feminist and a submissive woman. When my fiance and I decided to explore this side of our relationship, we agreed on certain boundaries: our BDSM play will never interfere with my family life (I am close with my parents and brother), my education or my career. He has been good about holding to this agreement -- for instance, he may punish me by making me wear certain clothes, but I never have to wear them to school or work-related events, or around my family. I am a professional stage performer, so we can't do anything that's going to leave marks on parts of my body that will be exposed, etc.
To be honest, for all of my sexually-mature life I have had fantasies about situations that would not be compatible with my worldview were they to happen in real life. But for me, it's quite enough to maintain the life I have with my husband, engage in role-playing with him in private, and enjoy some "alone time" with my more extreme fantasies.
It is a little disappointing to me that so few fellow posters seem to share my social views. But then, sharing a lifestyle choice doesn't mean that we have to agree on everything. My dom has a Masters' (appropriately enough) in English and is well-versed in gender theory and feminist criticism, and considers himself a feminist. If he weren't, well, things would be very different.