Truly-optimized PWR lattice for innovative soluble-boron-free small modular reactor

Area of Science:

• Nuclear Engineering
• Reactor Physics

Background:

• Small Modular Reactors (SMRs) offer advantages in scalability and deployment.
• Soluble boron is traditionally used for reactivity control in Pressurized Water Reactors (PWRs), but presents challenges.
• Developing Soluble-Boron-Free (SBF) SMRs requires innovative solutions for neutron economy and safety.

Purpose of the Study:

• To investigate novel fuel assembly re-optimization and burnable absorber (BA) concepts for a high-performance SBF SMR, named ATOM.
• To enhance neutron economy and inherent safety of the SBF PWR.
• To evaluate the performance and safety characteristics of proposed BA designs.

Main Methods:

• Introduction of a Truly Optimized PWR (TOP) lattice concept.
• Utilization and proposal of 3-D burnable absorber designs: centrally-shielded BA (CSBA) and disk-type BA (DiBA).
• Investigation of material, spatial self-shielding, and thermo-mechanical properties of CSBA and DiBA.
• Optimization of low-leakage two-batch fuel management for SBF ATOM cores.
• Coupled neutronic and thermal-hydraulic analysis.

Main Results:

• A combination of CSBA and DiBA achieved a small reactivity swing (<1000 pcm), long cycle length, and high fuel burnup.
• The moderator temperature coefficient remained sufficiently negative throughout the cycle.
• Small excess reactivity was managed by mechanical shim rods with minimal impact on local power peaking.
• Cold-zero shutdown was achievable with a pseudo checker-board control rod pattern.

Conclusions:

• The proposed re-optimized fuel assembly and innovative BA designs are effective for high-performance SBF SMRs.
• The ATOM core design demonstrates enhanced inherent safety features and efficient fuel utilization.
• The study validates the feasibility of SBF operation in SMRs with improved operational flexibility and safety margins.