If you're in Rhino, then open Rhino, go to Scene Manager > Output, set Scattering to 0, then click Presets > Defaults > Store Current. If you're in Cinema, set Scattering to 0 in a Scene object, go to Output > Scene Presets, click Save to Preset file, and overwrite the default_scene.xml file that you'll find in the plugin's /res directory.
Scattering should already effectively be 0 by default, because by default, it is disabled. It is a bug in the engine that it's being rendered anyway - it's not that way intentionally. If you're already in maxwell.exe, and it's rendering with Scattering when it should not, it is enough to enable then disable Scattering - you don't even have to stop the rendering.