About 30 senior sailors at the U.S. Navy's Charleston Nuclear Power Training Unit were being investigated for alleged cheating on an exam, the chief of naval operations said on Tuesday. The U.S. Navy officials were taking quick action to investigate the situation and apply corrective measures after the incident came to light on Monday, U.S. Navy Adm. Jonathan Greenert told reporters at a Pentagon news conference. The qualification exam was allegedly shared among some senior enlisted operators of nuclear power plants. But both Greenert and Navy Adm. John Richardson, the director of the Naval Nuclear Propulsion Program, stressed the incident did not touch on nuclear weapons. "Whenever I hear about integrity issues, it's disruptive to our units' success and it's definitely contrary to all of our core values -- our Navy core values. And it affects the very basis of our ethos," Greenert, the Navy's top officer, said. He pointed out the fact that senior enlisted sailors were involved made things more disappointing. "We expect more from our sailors, especially our senior sailors, and we demand it in our training and in our operations," he added. Richardson took full responsibility for the incident. "This is mine to investigate and to correct," he said. The cheating took place in the school in South Carolina, which is held on two converted submarines used as training reactors to certify operators to report to the fleet. "This incident involves members of the school staff who are required to qualify to operate and instruct students on the training reactor," Richardson said. The training reactors were shut down for routine maintenance once Navy officials learned of the incident.