That could work. I'm obviously not developing the game so whatever I say has no inherent value, but how would you respond to the idea that ALL of the wasteland biome is radiated, just to varying amounts. The larger cities and the craters that exist in between settlements contain the greatest concentration of radiation and in order for the player to enter those zones they would need a hazmat suit and/or they would need to chug some drugs that could only rarely be found in loot that protect them for a limited amount of time; whether the hazmat suit would degrade or not if for a separate discussion. On the other side of the spectrum, the small towns, roads/paths, and small towns contain much smaller pockets of lesser concentrated radiation. When entering the wasteland biome the player is given a debuff that is similar to stage 1 of infection - it has no immediate side effects but will only get worse if left untreated. Once this debuff reaches 100% (say, after 120 minutes) the player's immunity level reaches zero and they start taking damage from radiation poisoning. The player must then consume a drug or wear a hazmat suit (either of which probably won't be available at that point in the game) thus they must exit the biome. Another "debuff", a timer really of about 120 minutes, would then begin counting up representing the player's immunity level. If the player enters the wasteland unprotected before the counter reaches 100% then this timer would reset back to zero and the player would immediately start taking damage until they leave the wasteland once more. This somewhat artificial system would lock the player out of building in the wasteland until the mid- to endgame while still providing them with ample time to enter the biome, raid some joints, hold down for a night or two if required, and then escape by the next morning or afternoon assuming they had entered the biome in the morning on the first day. Having a system like this in place would also help to prevent players from entering the wasteland biome and loot there non-stop early game, assuming they could survive the tougher zombies, to exploit the higher gamestage/lootstage they would experience in this biome.