Primecoin client using so much CPU in background?

I downloaded the primecoin client but I saw that even when I wasn’t mining, just having it running and syncing the blockchain was using up 30-40% of my CPU (i5-2500k). Is this normal?

I also have a second question - if I leave it running on my home computer and mining on all cores, since it’s always using 100% of the CPU will it fry the CPU after awhile? Is this a good idea or is it recommended to build a separate rig if you want to mine at all?