An innovative core design for a soluble-boron-free small pressurized water reactor

Abstract

Summary This research investigates the neutronic feasibility of a high‐performance soluble‐boron‐free (SBF) small modular reactor (SMR) core based on a new burnable absorber concept called the “Burnable Absorber‐Integrated Guide Thimble” (BigT). Three unique BigT designs were loaded into the core; each BigT design was judiciously ascertained from the core radial power profile to tailor the required reactivity depletion patterns for an SBF operation. The approach is demonstrated to work well as the SBF SMR design exceeds the targeted cycle length while successfully controlling its burnup reactivity swing between 634 and 800 pcm throughout most of its operation. This paper also describes the use of hafnium‐doped stainless steel as mechanical shim (MS) rods to attain the core criticality. Because the worth of the MS rods is relatively small, insertion and withdrawal of the rods during operation hardly alter the core radial power distributions. The resulting axial power profile, meanwhile, displays a more refined bottom‐skewed pattern during the early portion of the irradiation cycle due to partial top‐half insertion of the MS rods. This investigation further deliberates on a modified checker board control rod pattern to assure safe cold shutdown of the core. All calculations in this multiphysics assessment of the 3D SBF SMR core were completed by using a 2‐step Monte Carlo deterministic hybrid procedure based on the Monte Carlo Serpent and COREDAX diffusion codes with the ENDF/B‐7.1 nuclear data library.

Fabrication of oxide pellets containing lumped Gd2O3using Y2O3-stabilized ZrO2for burnable absorber fuel applications

“…2 The use of control rods to compensate for this excess reactivity produces a nonuniform axial power distribution and incomplete burning of the fuel. [4][5][6] The main requirements for BA materials are (1) a high neutron absorption cross section, (2) a burn-out rate matching the fuel (U-235) depletion rate, and (3) the absence of fission product poisons. 3 Conversely, one possible way to overcome these problems is maximizing the use of BAs.…”

Neutronic design and analysis of advanced long-cycle boron-free operation of a small modular reactor core with particle type burnable poison rods

“…On the other hand, the use of boric acid in the coolant leads to several disadvantages or complications in reactor operation and maintenance. Of these, the primary system of the reactor is complicated by a chemical and volume control system (CVCS) because it is associated with lots of pipes and subsystems (eg, purification systems), which increase the probability that small loss of coolant accident (LOCA) may occur from breaks in the pipes . Also, another issue related to the boric acid in the coolant is the corrosion of the system structures, which produce a huge amount of liquid waste and complicate system maintenance .…”

“…So a boron‐free core design requires a significant increase in burnable poison (BP) rods, which can also increase pin power peaking. In particular, optimization of the BP rods or the use of new BP rods is very important in designing a boron‐free reactor to minimize the excess reactivity change over the cycle, which reduces the movement of control rods . Also, the design of control rods and optimization of their insertion strategies are necessary to control the power distribution within the design constraints and to minimize the impact of rod ejection accidents (REAs), which should be considered in boron‐free reactors.…”

“…[2][3][4][5][6] Also, another issue related to the boric acid in the coolant is the corrosion of the system structures, which produce a huge amount of liquid waste and complicate system maintenance. [2][3][4][5][6] In addition, a high boron concentration at the beginning of cycle (BOC) makes the moderator temperature coefficient (MTC) less negative or positive, and a positive MTC is usually not allowed (due to reactor safety), even if a very small positive MTC is sometimes allowed at BOC under hot zero power (HZP) conditions. 7,8 For example, the Nuclear Design Report 8 for YongGwang nuclear power (YGN) unit 3 cycle 1 allows a positive MTC less of than 5 pcm/ o F at HZP.…”

“…In particular, optimization of the BP rods or the use of new BP rods is very important in designing a boron-free reactor to minimize the excess reactivity change over the cycle, which reduces the movement of control rods. [3][4][5][6] Also, the design of control rods and optimization of their insertion strategies are necessary to control the power distribution within the design constraints and to minimize the impact of rod ejection accidents (REAs), which should be considered in boron-free reactors. In addition, the frequent use of control rods under a high-flux environment can cause a practical issue related to the integrity of control element assemblies.…”