Developments of zero-power noise methods for fast reactor systems

Kapitel i bok, 2025

This chapter deals with the extension of the pulse counting-based reactivity measurement methods, such as the Feynman- and Rossi-alpha methods for next generation systems. As mentioned in the previous chapters, one important feature of the Gen-IV reactors is that they will have a fast-neutron spectrum. The consequences of this fact and the need for extending the theoretical basis of the reactivity measurement methods for two-group theory will be discussed in Sections 6.2 and 6.3. Also, other aspects, such as availability of detectors and the need of including gamma photon counting into these methods, will also be discussed (Section 6.4). Section 6.5 summarises the principles of the two-detector Feynman-alpha measurement. Further, although they are not at the moment the main priority for next generation reactors, accelerator-driven systems (ADS) were a very promising candidate a couple of decades ago, and they are still potentially interesting. These systems will be driven by neutron sources whose statistical properties are very different from those of the traditional simple Poisson sources, hence the Feynman- and Rossi-alpha methods need to be modified for using them in such systems. This extension has already been made [6], but it will be briefly summarised in Section 6.6. Finally, one development, recently initiated for present reactors, as well as for safeguards problems, but of which the Gen-IV systems and small modular reactors (SMRs) would also largely benefit, is a new method to extract the same statistical information from the continuous signals of ionisation and fission chambers than from the pulse counting methods. Due to it being a new method with a limited number of publications, it will be described in Section 6.7 with some real examples of its use.