Actinide breeding and reactivity variation in a thermal spectrum ADSR – Part 1: Development of a lumped thermal reactor model

The beneficial properties of fast reactor systems in being able to both burn and breed actinides have led to renewed interest in this technology as a means of providing a more sustainable form of nuclear power production. However, despite significant investment over many years in the development of the technology, fast reactors have never been deployed in significant numbers. In view of the difficulties encountered in fast reactor development, enhancements to the existing, well proven light water reactor (LWR) technology may provide a more accessible path to improved sustainability.In this context, this paper describes the development of a reactor model for the purposes of examining performance of a typical pressurised water reactor (PWR) as a means by which extended fuel cycles and reduced waste production may be achieved in a thermal spectrum accelerator driven subcritical reactor (ADSR). This is achieved using a homogeneous lumped thermal reactor model that can simulate the evolution of actinides in a typical PWR to first-order accuracy. The accuracy of the model’s predictions is compared with the analysis of samples taken from operational PWRs. Although the model provides only first-order accuracy, it offers the advantage that it can calculate in seconds the evolution of nuclides which might otherwise take significantly longer using more elaborate models. The model provides a means by which the limitations and constraints affecting the operation of critical thermal reactors can be examined in Part 2 of this paper.

► We develop a lumped thermal reactor model.
► The model’s predictions are compared with actual PWR results.
► The variation of the 240Pu cross-section with burn-up is necessary to achieve reasonable results.
► The model is capable of representing the evolution of actinides within a typical PWR.