A consistent study was conducted on the total or partial elimination of soluble boron within the framework of the French Commissariat à l'Energie Atomique/Nuclear Reactor Directorate/Innovation Program. Three options were studied: maintaining the soluble boron during cold shutdown; soluble boron only for accident conditions; total elimination of soluble boron. The approach used to identify the motivations that guided the studies on soluble boron reduction or elimination is summarized, and the essential results are presented.

After a brief presentation of the objectives of these studies and of the results available in the literature, we comment on the safety means in use (for present reactors) as well as the options, of generic nature, which lead to increased safety in future reactors. The implications linked to the use of soluble boron in the coolant are described. The consequences for the reactor are briefly analyzed in terms of demands for reactivity control reinforcement and for the implementation of a functional redundancy.

The modifications in the architecture of elementary systems are briefly examined. The systems affected by soluble boron are identified as are the solutions envisaged for the three options. The influence of the control mode, without soluble boron, on the design of the plant is mentioned. The orientations in the design of new mechanisms to minimize the risks associated with rod ejection are also considered.

For the moment, only neutronic quantitative assessment has been achieved. Detailed and quantitative studies have not yet been performed on technological issues. The objective of this work is mainly to indicate the current motivations and to generate discussion and debate on the boron-free option.