They need a lot more then that.
NATO has missile defenses
and
10% is just enough to kill a whole bunch of civilians, but not enough to cripple. However, the return strike would end Russia. One thing this war has shown is NATO weapons go bang quite reliability.
I think nobody actually knows how much Russian's WMDs will actually work, including Putin. Putin clearly did not understand the capabilities of his army. In that position, even if the leadership was predisposed to nuking something, would they risk it?
If they toss a WMD at Ukraine and it malfunctions, it is going to be a deer in the headlights moment for Russia.