Hundreds of teen-agers are raped or sexually assaulted during their stays in the country’s juvenile detention facilities, and many of them are victimized repeatedly, according to a U.S. Department of Justice survey.

The teens are most often assaulted by staff members working at the facilities, and fully 20 percent of those victimized by the men and women charged with protecting and counseling them said they had been violated on more than 10 occasions.

“Today’s report illustrates the fundamental failure of many juvenile detention facilities to keep their youth safe,” said Louisa Stannow, executive director of Just Detention International, a California-based health and human rights organization.