Be like the evil Eledore and eliminate the cause of your concern.
Microwave the wifi router, then you no longer need to wonder if there is interreference when the router is no longer working.

Also yes, a microwave outer shell will diminish the radiation a lot, but it isn’t perfect. It will blast noise that your wifi signal will be susceptible to.
But how about you get a 5ghz Access-Point and place it in another location, you can keep your wifi-router as a router and/or spare/guest/shit wifi.