16.1. INTRODUCTION/OBJECTIVES

In parallel with current experimental research programmes, there are many activities devoted to improved model and associated computer code developments. Prior to plant application, these are validated against experimental data usually enveloping their application. With the increasing cost of experimental research, the improvement of models and the advent of faster and faster computers, the proportion of theoretical work in comparison to experimental work is increasing.

Computer codes are required for both design substantiation and safety analysis. The emphasis in this chapter will be mainly on the methods that have been developed and are available for safety analysis. A wide range of methods and codes have been developed and validated for current generation plant. This chapter examines the present status of research for current generation plant together with the implications for advanced applications. Current research is not only targeted towards more advanced modes of operation of existing plant but also for application to advanced, particularly evolutionary, plant applications. In many instances, code validation for current plant remains valid for evolutionary plant. This chapter does, however, describe how new phenomena relevant to evolutionary plant can be modelled, e. g. associated with passive system performance.

This chapter considers the role of different types of codes, integral, system, lumped parameter, computational fluid dynamics (CFD) and other specialist codes in the context of reactor design and safety research. More stringent safety standards imply more exacting quality assurance standards for all levels of code development, verification, validation and applications. Advanced software techniques offer more automated tools. Modern computer platforms enable detailed safety analyses to be performed that were not feasible at the times of licensing of many of today’s plants. These theoretical topics are covered.

The primary focus of this chapter will be on water reactor technologies. Water reactors occupy the overwhelmingly largest fraction of existing reactors in operation today and the nearest term evolutionary reactors are also likely to be of this type.

Analytical methods have been developed for other reactor types and some of these will be developed further as the innovative gas and liquid metal reactors’ concepts move forward. They will receive a brief mention in the last section of this chapter on innovative reactors. Analytical methods developments for the innovative reactors will proceed in parallel or slightly behind the corresponding experimental programmes that will be needed to develop innovative reactor technology. The latter were described in the previous section.