Serpentine belt popped off. Something locked up

1995 Cadillac deville 4.9L V-8, (175,000 miles) last night sepentine belt broke and something locked up. The engine continued to run, but of course every message came up on the board because nothing was turning at the time. Earlier during the day, a raddling noise was heard while the car was running and periodically would stop, but was really noticed during steering. This happened last year and was repaired. Mechanic said that a "pulley?" Locked up causing the belt to break. Does this happen annually? I bought the car used last year. Never had any other problems with it. Have driven it from New Orleans to Memphis twice with no problems.