Case study

Graphite modelling of ageing nuclear power generation assets

Frazer-Nash has a long successful history in understanding and supporting the ongoing operations of graphite reactors in the UK.


The UK’s nuclear power fleet of advanced gas cooled reactors (AGRs) are coming to the end of their generation lives. The end of generation dates have already been extended beyond their original designed dates and there is a requirement to ensure the ongoing safety of the reactors.

One of the main life limiting factors of the AGRs are the graphite reactor cores and their structural integrity after many years of high temperature irradiation and radiolytic oxidation. Understanding the degradation of graphite through life and forecasting into the future is vital for the ongoing operation of these reactors.

Our approach

Frazer-Nash has a long successful history in understanding and supporting the ongoing operations of graphite reactors in the UK. Previously supporting MAGNOX, we utilised knowledge of graphite material science to support the AGRs in numerous ways including:

  • Graphite data collation and management
  • Model development and calibration
  • Making forecasts of graphite brick behaviour
  • Continuously validating models against latest data.

Employing this cycle of model development and deployment, we were able to provide lasting support to the AGRs, continually improving the understanding of the reactor core and ensuring safe operation. This included supporting the development of safety justifications and engagement with the regulator, the ONR. We have an in-depth knowledge of the degradation of graphite under high temperature irradiation conditions and are able to make predictions of assets to extend their design life.

We employed our knowledge of graphite with a model development and deployment cycle to support and extend the operation of the ageing UK AGR fleet.

Support to graphite material test reactor experiment

The challenge

As the UK’s advanced gas cooled (AGR) fleet neared the end of their design life, there was a requirement to safely extend the end of generation dates.

One of the more significant limitations to the extension of the AGR's life is the graphite reactor core, due to its degradation under high temperature, irradiation and radiolytic oxidation conditions. Therefore, in order to support the safety cases to extend the life of the AGRs, the licensee required material properties data from highly irradiated graphite material.


Our support

Frazer-Nash Consultancy employed its breadth of knowledge of graphite material properties and modelling to support a material test reactor experiment with NRG at Petten. We supported the entirety of the experiment including the following activities:

  • Defining the requirements for the experiment in terms of required irradiation dose and oxidation, in addition to defining the testing requirements for the graphite samples
  • Data analytics of the acquired measured data including outlier analysis and database management
  • Assessing the acceptance criteria of the experiment and ensuring the original requirements were met
  • Using the measured data to validate and subsequently calibrate the models used for making predictions of graphite material.

Analysing the graphite data included investigating and understanding differences in the dimensional change, dynamic Young’s modulus, coefficient of thermal expansion, strength, thermal conductivity and electrical resistivity of the graphite, amongst other material tests. We were able to take advantage of the data to its full value and improve the modelling and understand of the graphite reactor cores to support life extension.


Delivering understanding

We utilised our knowledge of material science, combined with advanced data analytics and modelling approaches to support the completion of a graphite material test reactor experiment which met the requirements to a very high standard and quality. This led to a significant increase in the understanding of the graphite in irradiation conditions and supported the extension of life to the aging assets.