No injuries were reported following an explosion at an underground utility vault next to the Providence campus of Johnson & Wales University. National Grid spokesman David Graves said the utility was notified of the explosion just before 6 a.m. Tuesday. Graves said the blast occurred in a vault buried under a sidewalk on Pine Street. Two university buildings lost power. Graves said the cause is under investigation. University spokeswoman Madeline Parmenter said nearly 1,000 students were evacuated from two dorms as a precaution and were let back in a few hours later.