How to disable nether portals in a specific world?

Hello, so i'm making a server with npcs and you can select what type of server you're playing. For example: there's 2 npcs, box and survival and you choose what server you want to play. So i want to disable nether portals in the box world, but it needs to work in survival world. I use multiverse core and if you don't understand something, be free to ask me quiestions