There is described a fluid treatment system which may which may be used with radiation sources that do not require a protective sleeve—e.g., excimer radiation sources. An advantage of the present fluid system treatment is that the radiation sources may be removed from the fluid treatment zone without necessarily having to shut down the fluid treatment system, remove the fluid, break the seals which retain fluid tightness, replace/service radiation source and than reverse the steps. Instead, the present fluid treatment system allows for service/replacement of the radiation sources in the fluid treatment zone during operation of the fluid treatment system.