Subject: How far does a planet need to be from a nova to survive it?

I'm writing a science fiction book based on a planet in a cataclysmic variable
solar system. I want to know the effect a nearby nova (occuring at a distance of
say, 1 to 5 AU's from the planet in question) on the planet's atmosphere and
population etc. If the effects are catastrophic, how far does a planet such as
Earth need to be for the life on its surface to survive it, relatively intact?
The nova (in my book) are meant to be recurrent - occuring every 100 years or
so, so I don't want a major extinction every one hundred years. Please assume
the planet in question survived the initial supernova that created the white dwarf.

Your help in this matter would be MOST appreciated! Guesses are welcome too.

Re: How far does a planet need to be from a nova to survive it?