There is a new IAEA Safety Standard on site Evaluation that states that:
2.29. The external zone for a proposed site shall be established with account taken of the potential for radiological consequences for people and the feasibility of implementing emergency plans, and of any external events or phenomena that might hinder their implementation. Before construction of the nuclear installation is started, it shall be confirmed that there will be no insurmountable difficulties in establishing an emergency plan for the external zone before the start of operation of the installation.
Where the “external zone” is the likely future UPZ, by default 25 km.
It’ll be interesting to see how the ONR seek to establish off-site planning around new build especially as they want the Local Authorities to take the lead.