There is described a radiation source module for use in a fluid treatment system. The radiation source module comprises: a housing having an inlet, an outlet and a fluid treatment zone disposed between. The fluid treatment zone comprises a first wall surface and a second wall surface interconnected by a floor surface. The first wall surface, the second wall surface and the floor surface are configured to receive a flow of fluid through the fluid treatment zone. The radiation source module further comprises at least one radiation source assembly secured with respect to the first wall surface and the second wall surface and a module motive coupling element connected to the housing and configured to be coupled to a module motive element to permit the radiation source module to be installed in and extracted from the fluid treatment system. A fluid treatment system comprising the radiation source module is also described.