Computer-aided modelling and virtual prototypes play a continuously increasing role in supporting and driving the design of new and more advanced components, structures and systems. On this basis, digital twin technology have attracted increasing attention in several industrial sectors, thanks to their capability of providing a better understanding of the physical assets, allowing to optimize systems design, manufacturing, operation and maintenance, with unquestionable enhancements in terms of both safety and cost efficiency. The Digital Reactor Design (DRD) project represents a first step toward the introduction of digital twin tools in the nuclear sector. Indeed, the main aim of the project lies with the implementation of a fully developed digital environment for computer-aided modelling able to capture the different phases of reactors design in a coherent, unique framework, which would ultimately result in the implementation of a reactor digital twin. This latter consists of a virtual representation of the nuclear physical system, able to reproduce and hence predict, through the use of advanced computational tools and models as well as the continuous collection of data, the behaviour and state of the system across its entire lifecycle, with unquestionable enhancements in terms of both safety and cost efficiency. The integration of the OpenCossan library within the overall digital framework, provides cutting-edge uncertainty quantification tools, able to validate and test the robustness of the models and methods adopted and hence enhancing the credibility of the ultimate tool, understood as the willingness of designers, regulators and operators to trust the information provided and to make decisions based on the model output.