The challenge

Nuclear energy provides approximately 20% of the UK’s electricity and is a key source of low-carbon energy. However many of the UK’s older, graphite core reactors are reaching the end of their estimated life cycle and new nuclear plants are yet to be available.

Therefore it has become necessary to extend the plant life of existing power stations to provide electricity until new facilities are operational. In order to do this, ageing components and materials must be maintained in working order to ensure the energy production remains safe and reliable.

Advanced Gas Cooled Reactor (AGR) cores are multi-layered arrays of graphite components whose geometry and mechanical properties change under prolonged exposure to neutron irradiation. The presence of cracked components in the arrays later in their operational life may cause disruption of core geometry with implications for fuel cooling and control rod insertion in the event of a severe, but infrequent, seismic event.

What we're doing

These ageing issues are being addressed using physical models of an AGR core which has been built in the Faculty of Engineering to provide experimental validation for the computational tools which model high levels of core degradation. The rig has been tested on the shaking table with the purpose of exploring the mechanical interactions inside the array and to output acceleration and displacement data at selected locations. The model rig is capable of providing experimental evidence for the computational modelling methods and is making significant contributions to reducing uncertainties in these methods.

Tests carried out by the PLEX team on the physical model in the lab are mirrored in the numerical model by the Atkins team. Once the university has analysed and validated the data received from testing the physical model, comparisons are made with the numerical model.

The project is led by the University of Bristol in close collaboration with EDF and Atkins, who manage the GCORE modelling system for EDF.

How it helps

This project gives a better understanding of the behaviour within an aging graphite core in the case of a seismic event, and supports the justification of plant life extension.

Evidence that a graphite core near the end of its design life can still be operated and shutdown safely after a seismic event.

Further benefits of this project are:

• Reassurance in the output of the EDF numerical modelling systems.
• Evidence supplied by the University feeds into the Safety Case presented quarterly to the Office for Nuclear Regulation.