The big damage from a nuke is the shock front of the explosion, heat, and radiation.
In a vacuum, there's no medium for a shock front to propagate so we can forget that.
As for the heat and radiation released, we regularly fly our ships through solar prominences, coronal mass ejections, and the jet cones of neutron stars.
For comparison, take the largest nuke ever created by mankind, the Tsar Bomba, and detonate roughly two billion of them - you'd maybe match a single second of Sol's energy output.