The final stage of a complex jacking operation takes place this week, with an attempt to slide a 110m long steel frame building over concrete tanks full of radioactive waste sludge at BNFL's Sellafield reprocessing plant in Cumbria. The 10, 40 year old tanks are deteriorating and must be enclosed before being emptied. Safety considerations forbid crane operations directly above the tanks, so the pounds23M portal frame building must be erected off line and the entire 2,800t structure slid in stages over the waste. The last of seven separate slides involves contractor Balfour Beatty Construction and specialist subcontractor Hevilift, using 46 computer co-ordinated jacks to first raise the building by 15mm. It will then be slid 15m along PTFE coated rails.