Public protection will be a "top priority" in controversial plans to open a super prison in Port Talbot, the Ministry of Justice has said.
The UK government announced in March that it planned to build a new prison on undeveloped land in Baglan.
Objectors have raised concerns the proposed site is too close to schools and homes.
But the MoJ said no prisoner would be given temporary release unless they passed a "risk assessment".
Dozens of people attended a public meeting against the plans on Monday and heard from former inmates about their time behind bars.
Mari Arthur, who helped organise the meeting in Llanelli, said: "There are more cells in Wales than there are people to fill them.
"The massive prison in north Wales is half empty, so I don't know why they want to build a massive prison in the south."
Cleif Harpwood from Baglan questioned the "practicality of the project".
"The roads around the area are full already... the traffic is going to be a nightmare," he said.
The land on Baglan Industrial Park, owned by the Welsh Government, was chosen by the MoJ out of 20 potential sites.
BBC Wales understands the proposed prison will be designated Category C with space for up to 1,600 prisoners, although that has not yet been confirmed by the MoJ.
Bethan Jenkins, AM for South Wales West, said large prisons were "not going to help prisoners rehabilitate themselves" and research "showed a prison of this size is too big for an area like Port Talbot".
An MoJ spokesman said it would "fully engage with the local community" as it developed plans.
"Public protection is our top priority and temporary release is only granted to offenders who pass a thorough risk assessment," he said.
"We are investing £1.3bn to modernise the prison estate, closing older prisons that are not fit for purpose and creating in their place high-quality, modern establishments."