microwave fuse out

Microwave has shut off with fuse out. Enough to kick off the circuit breaker. When I reset the circuit breaker, the internal fuse in the unit is blown. I replaced the internal fuse and the unit worked for about 12 hours and then did the same thing again. Kicking the circuit breaker and blowing the internal fuse. Any ideas on what could be causing this. Thanking you very much in advance for your responses.