I think, it's not really meaningful to talk about blast radius in the traditional sense in outer space nuclear detonation. The blast effect on earth seen is caused mainly by very hot expanding air. There is no air in outer space and therefore will be no shock waves, with most of the energy being high intensity radiation. The effectiveness of nuke detonation in space against hard targets, like meteorites, is a lot less than you might think.There is a formula for the calculation of the radius of a nuclear blast when detonation is done on earth.
How do you detonate a nuke in space？
You can talk about the effective distance from the explosion that sats equipment will be fried by the EM energy.