See FT article here.
There are two quite separate themes going on here: evacuation and relocation. The former is about running away from an airborne plume and is an urgent action. The later is a longer term issue.
For prompt evacuation the debate is about what dose do you have to avert for it to be worth running. For an elderly or infirm person, where evacuation may cost their life, the averted dose would have to be well up in the range where deterministic effects kick in hard (but there is a added complication if their carers all want to run). For an infant, able to see evacuation as an adventure if the adults around them are not too visibly stressed and with longer for stochastic effects to hit, the trigger level of avertable dose is much lower. It is not easy to put numbers to these trigger levels, not easy to estimate avertable dose in the heat of the moment and not easy to reassure a population being hit with both radiation and media outpourings. Decision makers are in a hard place!
For relocation, there is more time to take measurements, more time to talk to the people affected and more time to reach a decision. Still a hard place to be. The balance is between the disruption to people’s lives if they have to move permanently, particularly if they cannot recover their belongings and if the receiving population is negative in any way, and the worry about living in an area with elevated contamination levels. Experience shows that either way some of the people affected are going to need support for a long time to come.
There are no easy answers.