Assessment of the Design and Safety Properties of PWR Cores With Reduced Soluble Boron Utilization

In conventional pressurized water reactor (PWR) designs, soluble boron is used for reactivity control over core fuel cycle. As high boron concentrations have significant impact on reactivity feedback properties and core transient behaviour, design changes to reduce boron concentration in the reactor coolant are of general interest in view of improving PWR inherent safety. In the framework of an investigation into the feasibility of low boron design, two PWR core configurations based on fuel with higher gadolinium and erbium utilization have been developed permitting to reduce the natural boron concentration at begin of cycle by approx. 50% resp. 30% compared to current PWR technology. Their performance was compared with the one of a standard German PWR core in a loss-of-feedwater anticipated transient without scram, boron dilution scenario and a hypothetical beyond design basis accident. Moreover, this paper deals not only with the potential advantages, but also addresses the drawbacks of the new PWR configurations — complex core design, increased power peaking, significant amount of non-burnable gadolinium and erbium isotopes, reduced cycle length, etc. The analyses presented here were supported by detailed cell, diffusion and thermal-hydraulic simulations, performed with the well known codes HELIOS, QUABOX/CUBBOX and ATHLET.