The US Nuclear Regulatory Commission has cited the Massachusetts Institute of Technology for two violations related to the exposure of a research reactor worker to a surprisingly high dose of radiation, a spokesman said Thursday. On Oct. 17, the university, in Cambridge, reported that one of the reactor's operators had a radiation measurement of more than four rems for the period between July 1 and Sept. 30. That accounts for more than 80 percent of the total radiation that a worker can be safely exposed to during an entire year. All other employees' radiation exposure measurements for the same time period were normal. A report released following a special NRC inspection says MIT failed to make reasonable checks to evaluate the magnitude and extent of radiation levels present at work areas as required by the federal regulator, NRC spokesman Neil Sheehan said.