Effect of operating pressure on the performance of a hybrid system of small modular boiling water reactor with external superheaters

Highlights: • Conceptual design of hybrid Small Modular Boiling Water Reactor (SMBWR) with external superheaters is proposed. • Superheater can allow load-following and improve the thermal efficiency of SMBWR. • Operating SMBWR at higher pressure (up to 10.0 MPa) has no significant neutronic effects. • A load following capability (down to 65%) is demonstrated for the hybrid system. • Variable demand can be met by the hybrid system with the reactor operating at full capacity. - Abstract: With the increased role of intermittent renewables in the energy mix, it is important for the Nuclear Power Plants (NPPs) to develop flexible load-follow capabilities in order to be economically competitive. By combining NPP with external superheaters, there is possibility to increase power conversion cycle efficiency and reduce load to some extent while maintaining the nuclear reactor operation at 100% of its rated power and thus maximizing its economic value. In this paper, parametric study of a Small Modular Boiling Water Reactor (SMBWR) conceptual design combined with external superheaters is presented quantifying its performance at different system pressure. The first part of the work is focusing on how operating pressure will affect the SMBWR system as a whole, which includes neutronics, thermal hydraulics, and thermodynamics. WIMS-PANTHER package and COBRA-EN were used as the neutronic and thermal hydraulic tools. In addition, MATLAB models of the SMBWR natural circulation loop and balance of plant were developed for the study. The second part of the work examines the maneuvering capability of SMBWR. It is found that increasing the pressure from 6.5 to 10.0 MPa has no significant neutronic effects, while thermal efficiency is slightly improved. It is also found that SMBWR is able to reduce the load to 65% while maintaining the reactor power at 100% of its rated value.