Office for Nuclear Regulation

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Graphite core of AGRs

The UK has a long history of using graphite as a moderator from the early Magnox reactors to the Advanced Gas-cooled Reactors (AGRs). The moderator slows down the speed of neutrons produced during nuclear fission and helps to sustain the chain reaction so that the heat can be used for electricity production. In both of these designs, the core is constructed from thousands of interlocking graphite bricks which also form a large number of important channels.  These channels contain the nuclear fuel, the reactor control rods and allow the passage of carbon dioxide coolant gas to remove heat from the reactor fuel and core. 

There are two current issues associated with graphite bricks:

ONR's mission is to provide efficient and effective regulation of the nuclear industry, holding it to account on behalf of the public.  ONR would not allow the continued operation of any reactor unless it was safe to do so. 


The UK fleet of AGRs are now the only power producing nuclear reactors in the world that have a graphite-moderated, carbon-dioxide cooled core.  Therefore, the technical community supporting the AGRs is small in relation to that for water moderated reactors and there is a lack of comparable experience outside of the UK. 

For several years, ONR has focused on creating and developing a number of independent sources of expert advisors that can conduct research to develop independent models. 

A graphite technical advisory committee was formed in 2004, consisting of senior academics and other internationally recognised experts in nuclear graphite technology, which continues to provide authoritative advice to ONR and enables us to provide appropriate, authoritative challenge to the licensee's own analysis.

In addition, ONR now supports research groups at several universities including Manchester and Birmingham, and has commissioned the Health and Safety Laboratory to carry out work on our behalf and provide advice to assist in our assessment of the licensee's safety cases for graphite.