Hunterston ‘A’ Nuclear power station, West Kilbride, Ayrshire, was shut down in March 1990, and is in the process of being decommissioned.
The licence holder for the site, Magnox North (formerly BNFL), has commissioned a number of parties under an alliance agreement to specify, design and construct an intermediate level waste store (ILW) for the long term on-site storage of the waste material. Halcrow was appointed to provide support to the project in various roles including structural design, project management and quality assurance.
The initial stages of the project involved the concept design for the facility, including extensive soil-structure interaction analysis, structural analysis under the design basis earthquake, generation of secondary response spectra for design and margins assessment. The main analysis software included SAP2000, ANSYS and FLUSH.
The design was undertaken in conjunction with the mechanical engineering alliance partner and a wide range of structural options were considered, designed in concept and costed as part of a rigorous optioneering process. All design work was undertaken to American standards for the design of nuclear related concrete structures (ACI 349-01) and included consideration of structural performance at and beyond the design basis events.
The output from the optioneering was a preferred solution that was developed in detail and included consideration of the maintenance requirements and the longevity of the structure. The nature of the stored content of the facility placed significant requirements on the internal environment of the structure and constraints on in-service access to the facility. These aspects of the design were considered in detail and reported, leading to a number of recommendations to the final form and materials used for construction of the store.
A further aspect of the design considered by Halcrow was the stability of the waste packages within the store - stacked six and seven units high and potentially subject to seismic loading. A dual approach was adopted to qualify the stability of the packages:
- Review of testing of a full size package stack on a shaker table.
- Analysis of six and seven high stacks.
Advanced nonlinear analysis was used for the stack stability work and an extensive parametric study was undertaken, including consideration of various factors that affect the stack stability, such as:
- Store floor level
- Waste package mass
- Friction co-efficient between packages and package and floor
- Waste package construction tolerance
- Package eccentricity - mass
- Package eccentricity - placing tolerance
The main structure design was progressed to American standards and specialist advice was used to ensure a code compliant robust design.
The detailing of the design was progressed in close consultation with the Contractor to ensure that the required quality of construction could be achieved and that the detailed reinforcement drawings reflected actual construction methodology, together with other buildability and construction health and safety requirements.
Halcrow also acted as project manager throughout construction. The completed building was commissioned in 2008.