Monitoring the core
To monitor the condition of the reactors, graphite inspections are carried out at our two longest operating stations, Hunterston B and Hinkley Point B, every 12 to 18 months. Similar inspections are carried out at our other AGR stations during their statutory outages which take place every three years. The results of each of these inspections allow us to add to our understanding of graphite behaviour, and confirm that our reactors are ageing as expected.
Inspections carried out so far at Hunterston B and Hinkley Point B have identified a small number of cracked bricks in the core, but remain well within the safety margins for the stations. The findings are in line with our expectations for this stage in the stations’ lifetime, and do not have an impact on our future plans.
Over time, the graphite also slowly loses weight as part of the normal ageing process. This is a well-known phenomenon which was fully considered as part of the stations’ design and is factored into safety limits approved by the independent regulator, the Office for Nuclear Regulation (ONR). During statutory outages, we perform further inspections of the reactor core to confirm the level of weight loss to ensure that the weight loss remains within the limits agreed with the regulator.
Pressurised Water Reactors do not have a graphite core, so there are no similar issues at Sizewell B or in the design for the new station at Hinkley Point.