Hunterston A nuclear power station was closed down in 1990 and is now undergoing decommissioning.
The spent nuclear fuel was removed from the reactors in 1995, reducing radioactivity to less than 1% of the original operating levels.
The power station is being converted into a Safestore and Halcrow were responsible for designing the Safestore enclosure to the two 50m high reactor buildings. In addition to carrying out the reference design Halcrow prepared all the safety case documentation. The Safestore reactor buildings were designed to have an operational life of 100 years and the existing structure was designed to exist unheated during this period.
As consequence of this design requirement Halcrow carried out detailed modelling of the internal environment to determine the levels of condensation which are likely to arise throughout the buildings. This involved carrying out extensive 3D hydrodynamic simulations of the reactor buildings using Virtual Environment software which incorporated the Apache dynamic thermal simulation program. This analysis indicated that the proposed aluminium cladding system, Kalzip does not require an insulation layer in order to maintain condensation at acceptable levels.
The complex shapes of the reactor buildings are not covered by the existing UK wind standard (BS 6399 part 2). A comprehensive programme of wind tunnel testing was undertaken to determine the design wind pressure coefficients to be used for designing the Kalzip cladding and its supporting steelwork system.
Structural surveys were undertaken to determine the condition of the existing 50 year old steelwork and concrete structures. These surveys involved extensive intrusive examination of the concrete, which were complicated by the presence of radioactive contamination.
The new Safestore structures are designed for a range of extreme environmental loadings, the most onerous of which are wind and temperature.
This was a multidisciplinary project involving M&E, civil/structural, environmental and safety case teams supported by specialists in wind engineering, paint technology and probabilistic risk assessment. Halcrow successfully delivered this complex project to an accelerated design programme which had significant financial penalties for late delivery.