The application of portfolio selection to fuel channel inspection in advanced gas-cooled reactors

The continued operation of the UK's advanced gas-cooled nuclear reactors is dependent upon inspections of the graphite core to provide information on the evolution of core properties (such as the shapes of individual graphite bricks). It is necessary to optimise the information that is obtained, and the question of which fuel channels to inspect is a portfolio selection problem, complicated by the fact that the solution space is large and cannot be searched exhaustively. In addition, a number of portfolio-specific selection criteria must be applied, including the need to inspect channels in an even distribution across the core. A genetic algorithm is used to find a near-optimal solution, adapted so that portfolios potentially able to breed better offspring in future generations are accounted for. Analysis of the portfolios is an important part of the channel selection problem and algorithms have been developed to determine the significance of individual elements within the portfolio and the sensitivity of utility to portfolio size. The methods developed have been implemented in the CHANSELA software, the use of which contributes to the demonstration of the continued safe operation of the reactors.