Demonstrating the maintenance of the physical integrity of reactor cores which experience intense thermal and radiation stresses is a critical part of the safety case for their continued operation. Quintessa provides mathematical & statistical modelling and software development services in support of reactor safety cases.
An example is work carried out for EDF Energy on the evolution of graphite cores in Advanced Gas Cooled Reactors (AGRs) where Quintessa is providing support in a number of key areas associated with understanding the development of defects in the graphite bricks as they age, and the evolution of graphite properties with time.
Statistical methods have been used to enable the safe period of reactor operation to be calculated on the basis of the history of brick defects observed to date, and to help determine the optimum future inspection strategy. These methods are applied to each of the reactors when they are shutdown for inspection. The CoreStats code has been developed by Quintessa for EDF Energy specifically for this purpose. It is designed to complement process-based approaches by focussing on what information on future core behaviour can be obtained from historical data.
Furthermore, mathematical models are being used to understand a range of problems associated with the ageing nuclear reactors. For example, models implemented in QPAC have been used to gain a better understanding of gas flow and transport through graphite reactor cores, demonstrating that flow through graphite bricks is concentrated through a few pathways.