The reactor in the Dragon Building at Winfrith has been out of service since 1975, with the polar crane having had little use since that time. The decision to decommission this facility necessitated the refurbishment and reconditioning of the crane as a vital piece of equipment for both phase 1; the removal of the internals of the inner containment including all ancillary equipment around the reactor, and phase 2; the removal of the reactor itself.
The final solution comprises of two near-identical tool deployment mast and crane rigs, each covering two of the wet bays. On each rig, the crane and mast work in tandem; the crane removes and subsequently replaces the bay covers whilst the mast and its tooling down-sizes and then extracts the waste from the bays, which is then removed from site in a sealed container.
This refurbishment presented a difficult obstacle; the very limited space available around the reactor in which to remove the old and raise the new equipment into position, and the lack of another crane to utilise for the operation.
A full structural analysis revealed the original polar bridge to be structurally sound, so the replacement crab unit was designed to fit and equipped with two high integrity hoists; a 25tonne main hoist lifts the larger loads, and a smaller, more agile, 5tonne high integrity auxiliary hoist undertakes 95% of the handling duties.
Safety is ensured through secondary drive units on the primary gearboxes, emergency disk brakes mounted directly onto the rope drums, and over-speed relays, overload relays and shaft relays protecting against the crane running over its safe working load and speed limits.