While the unit is usually reserved for inmates who have been involved in an incident in the prison, Sheehan has been placed there for his own protection.
He has been isolated from the rest of the prison population in Cork because of concerns about his safety.
It follows the revelation in court on Tuesday at his sentencing hearing that he was a garda informer for two years.
He was sentenced in relation to the shooting of Ciara Sheehan, who is no relation, at her boyfriend’s home in Hollywood Estate, in May last year.
During the hearing, defending SC Vincent Heneghan told the court that his client was acting as an informer to An Garda Síochána for two years, up to Christmas 2015. He said his client supplied names of people involved in the drugs trade, gun trade and “criminality in general”.
Mr Heneghan also told the court at Tuesday’s hearing that Sheehan had been moved between three prisons, while he was held in custody since being convicted last November in connection with the shooting, for his own safety.