Abstract
The autonomous transportable on-demand reactor module (ATOM), a 450 MWth PWR-type small modular reactor (SMR), is under development at Korea Advanced Institute of Science and Technology (KAIST). The ATOM core is designed for soluble-boron-free and passive autonomous load-following operations by utilizing successfully an advanced reactivity control technology, centrally-shielded burnable absorber (CSBA). To enhance the ATOM core safety, CrAl-coated Zircaloy-4 is adopted as an accident-tolerant-fuel cladding. For a long operational cycle, the reference ATOM core has primarily accomplished with a single-batch fuel management (FM). In this paper, for more flexible operation and enhanced fuel utilization, various multi-batch FMs are investigated while the core performance is maintained in terms of both neutronic and safety aspects. These aspects are refueling pattern, cycle length, burnup reactivity swing, discharge burnup, axial and radial power peaking factor (PPF), total PPF, and temperature coefficients. Several refueling types are examined: In-out (low leakage), out-in (flattened power), and randomly scattered schemes. In addition, new heavy reflector designs, ZrO2 and PbO, are introduced instead of stainless steel reflector for an improved core performance. Moreover, a new CSBA loading pattern is also proposed for an effective reactivity control of multi-batch FM strategy. Numerical results show that with a two-batch FM the cycle length can achieve above 2 years with an average discharge burnup of 40 GWd/tU, while the burnup reactivity swing remains less than 1,200 pcm. On top of that, the coolant and fuel temperature coefficients are highly negative at the beginning of cycle and power profile is comparable to that with the single-batch FM. All calculations in these multi-physics assessments of the ATOM core are performed using a Monte Carlo-diffusion hybrid code system based on Monte Carlo Serpent 2 and nodal diffusion COREDAX codes.
Highlights
pressurized water reactors (PWRs)-type Small modular reactors (SMRs), one of Gen-IV reactor concepts, have gained significant international R&D efforts recently
A two-batch fuel management (FM) has been successfully developed by optimizing new centrally-shielded burnable absorber (CSBA) loading strategy along with several fuel shuffling schemes
The discharge burnup of the fuel is significantly enhanced compared to the single-batch FM, while maintaining a flat radial power distribution throughout the cycle
Summary
PWR-type Small modular reactors (SMRs), one of Gen-IV reactor concepts, have gained significant international R&D efforts recently These reactors, based on most advanced and mature technology, are designed to be multi-purpose, compact, simple and less dependent on active control means. A new CSBA loading pattern is proposed to attain a small burnup reactivity swing (BRS) during the cycle for SBF operation and considerably low power peaking. Both newly proposed radial heavy reflectors, ZrO2 and PbO, are applied to enhance the cycle length and compared to the reference SS-304 one. It should be noted that the two-step procedure is well validated against other nuclear regulator-approved codes [11]
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