the new intergrated blender/yafray combo seems to call yafray from within the blender terminal (under windows)
and this cannot be stoped without crashing blender.
does the esc key work or is it suposed to work?
if there is a way please tell me, because its a sd day when you cannot close a 3rd party render without closing your 1st party software and losing file info etc...
a 4 hour render or more that needs to be canceled shouldn't crash blender.