Feasibility Studies of a Soluble Boron-Free 900-MW(electric) PWR, Core Physics - I: Motivations, Assembly Design, and Core Control

Feasibility studies of an advanced 900-MW(electric) pressurized water reactor (PWR) aiming at the total elimination of soluble boron during normal reactor operation (extended uranium cycle length of 16 GWd/t) are summarized.

The neutronic consequences of this boron elimination on assembly design (poisoning, moderation ratio, cluster system, etc.) are presented. The specific assembly geometry has been optimized by taking into account a number of parameters, in particular the moderating ratio and thermal-hydraulic performances.

The modifications that must be made to a standard PWR are studied (loading pattern and control rod management) to control the core with the same safety criteria as for the standard PWR, during the whole cycle, from power operation to cold shutdown. A new control rod system, with two different kinds of control rod clusters, has been developed. The first allows power control during operation while the second ensures cold shutdown. It is shown that these modifications do not require different technologies from those of present PWRs.