Feasibility of Reduced Boron Concentration Operation in Pressurized Water Reactor Plants

The negative impact of a boron dilution accident on the safety of a current pressurized water reactor (PWR) initiated investigations with the aim of checking the feasibility of reduced boron concentration operation. In addition, reduction of the maximum boron concentration in a PWR is a practical and feasible means to substantially reduce the radiation dose to operators and to minimize corrosion damage. Four types of integral burnable absorbers have been considered: gadolinium, integral fuel burnable absorber (IFBA), erbia, and alumina boron carbide. Under consideration of four different kinds of fuel assemblies (FA), four core design candidates were developed by applying current PWR OPR-1000 technology and by keeping major engineering design constraints and the equivalent fuel enrichment level used in the reference core (REF) design. However, an optimal design was targeted to achieve comparable discharge burnup as well as favorable design safety parameters. The comparative analysis between the REF and the optimal core designs is presented here. One of the designs is suggested as the most promising and favorable low boron core (LBC) design in this framework. The proper combination of axial and radial enrichment zoning patterns plus a mixture of fresh FAs with depleted assemblies in an LBC design candidate with an IFBA-bearing FA at equilibrium cycle could bring a two times narrower axial offset variation than that of the REF design, maintain an acceptable power peaking factor [approximately]23% lower than the design limit, and achieve higher fuel burnup. It was observed that this optimal LBC design could comply with current OPR-1000 reactor acceptance criteria associated with smooth reactivity swing, more flattened power distribution, and desired limiting safety parameters despite an 18% loss of shutdown reactivity worth at beginning of cycle when compared to the REF design.