Halcrow was commissioned by British Energy to undertake the outline design, feasibility study, detailed design and subsequently independent technical assessment (ITA) of Boiler Closure Unit (BCU) external steel restraint (ESR) systems.
The ESRs will be installed at the Hartlepool and Heysham 1 nuclear power stations to prevent ejection of the BCUs and preserve the structural integrity and nuclear safety case arguments required to justify return to service, following the discovery of corroded pre-stressing wires in the BCUs. The work formed part of a £70 million project to facilitate and justify recovery of the power stations to service.
The detailed design and subsequently ITA involved a series of stability, nonlinear instability (buckling), thermal and seismic analyses of the proposed ESRs using full-scale ANSYS models developed from detailed CATIA CAD models. The work also considered the effects of asymmetric loading cases that could result from manufacturing imperfections and the possibility of the BCUs impacting on the ESRs asymmetrically after failure.
Associated with this project, Halcrow also offered expert advice for the preservation of the integrity of concrete BCUs, testing of physical models of the ESR and a peer review on the investigation of a stress-coring technique as a method for measuring residual pre-stress in the BCUs.