[en] British Nuclear Fuels Limited's (BNFL's) Waste Vitrification Plant at Sellafield is responsible for processing high-level radioactive waste. This history of the process development and the operation of the plant are outlined. Early operation experience revealed that the severe in-cell operating environment was causing high unreliability in several key items of equipment. Subsequent improvements to overcome these problems are outlined, leading to increased plant throughput overall. (UK)