Heysham 1 shares its reactor design with Hartlepool nuclear power station, which introduced the replaceable pod boiler design. The CEGB specified a compact design for the Heysham 1 and Hartlepool power station reactor islands in comparison to the design of the two preceding stations at Hinkley Point B and Hunterston B in order to reduce the capital cost, but this caused expensive construction delays because of restricted access. The Heysham 2 reactor island occupies a much larger footprint than Heysham 1 for a similar design output of power.