Fuel performance parameters are measured on-line in the Halden reactor by means of sophisticated instrumentation especially developed for in-reactor applications. Measurements cover continuous monitoring of fuel temperature, fission gas release, fuel swelling and cladding diameter changes due to, e.g., pellet-cladding interaction. An inspection compartment is utilised for additional investigations, e.g., for determination of the oxide thickness as required in Zircaloy corrosion studies. The Halden instrumentation capabilities are presented and discussed in the paper, together with more recent developments in the area of fuel rod refabrication and reinstrumentation.