Legal complications around its use - as it sits on military land - were also flagged, along with the lack of any budget to support the move.
A proposal to reopen an old military prison at the Curragh Camp has been dropped due to cost and legal complexities.
The Department of Justice had hoped to use the facility to ease severe overcrowding in Irish prisons.
But a feasibility review found the site would only create space for around 62 inmates and would require major structural work - including repairs for dry rot and poor roofing - making it financially unviable.
Internal documents, according to The Sunday Times, show the Irish Prison Service had raised significant doubts about the plan.
Legal complications around its use - as it sits on military land - were also flagged, along with the lack of any budget to support the move.
Despite early suggestions from prison staff that the site could be restored with minimal investment, further assessments revealed that extensive and costly upgrades would be needed to bring it up to standard.
Meanwhile, Ireland’s prison population has soared past safe capacity, with over 5,500 inmates now in custody.
860 more than the system was designed to hold.
Cork Prison is the worst affected, with every cell doubled up and nearly 90 prisoners sleeping on floors.
The Prison Officers Association says overcrowding is fuelling violence, drug abuse, and creating unsafe conditions for staff and inmates.
While the government plans to accelerate new prison builds, officers say emergency action, including reopening old facilities, is needed immediately.

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