6 Oct (NucNet): Cracks found in graphite moderator bricks at the Hunterston B-1 nuclear reactor in Scotland will not affect the reactor’s operation and have no safety implications, EDF Energy has said.
EDF Energy said every time a reactor is taken out of service for planned maintenance the graphite core, which is made up of around 6,000 bricks, is inspected.
During the current planned maintenance at Hunterston B, inspections revealed two bricks with a new crack. This is what was predicted during Hunterston B’s lifetime as a result of extensive research and modelling, EDF Energy said.
EDF Energy said: “It will not affect operations and we also expect that a few additional cracks will occur during the next period of operation. The small number of cracked bricks found during routine inspection is in line with our expectations. The findings have no safety implications and are well within any limits for safe operation agreed with our regulator.”
Hunterston B has two advanced gas-cooled reactor units (AGRs). Hunterston B-1 began commercial operation in February 1976 and Hunterston B-2 in March 1977.
Following press reports earlier this year about a related issue, graphite weight loss in AGRs, EDF Energy said it has a continuous programme of monitoring, sampling and modelling graphite behaviour.
Over time, graphite slowly loses weight as part of the normal ageing process. EDF Energy said 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 regulator, the Office for Nuclear Regulation.
“Graphite ageing is one area used to determine the lifespan of an AGR nuclear power station”, the company said.
In August 2014, EDF Energy shut down four reactors at its Heysham A and Hartlepool stations after it discovered a crack on a boiler spine at Heysham A-1. The Hartlepool plant has the same boiler design as the Heysham A units.
The company said it expects to restart those units in phases between the end of October and the end of December.
