Evaluation of high power density annular fuel application in the Korean OPR-1000 reactor

[摘要] Compared to the traditional solid fuel geometry for PWRs, the internally and externally cooled annular fuel offers the potential to increase the core power density while maintaining or increasing safety margins. It is demonstrated that for the Korean OPR-1000 reactor, power density can be increased by 20% when the 16x16 solid fuel assemblies are replaced by 12x12 annular fuel assemblies. In this annular fuel design, the assembly dimensions, coolant flow rate, and core outlet coolant temperature are kept fixed at the reference values for the OPR-1000 with solid fuel. The core inlet temperature is decreased to accommodate the additional 20% energy. Thermal hydraulic steady state analyses are carried out to determine the Minimum Departure Nucleate Boiling Ratio (MDNBR) margin and evaluate improvement in the design to maximize this margin. Whole core VIPRE-01 model results show that a proposed 14x14 annular fuel design cannot achieve high power uprate because of sub-limit MDNBR in the inner channel. To better optimize the 12x12 annular fuel design, the rod dimensions are fine-tuned by slightly increasing the inner channel diameter and outer channel diameter, while keeping the fuel to moderator ratio fixed. The modified design can achieve 20% power uprate. In addition, MDNBR sensitivity to manufacturing tolerances is investigated, showing that the new proposed design can accommodate typical manufacturing tolerances. Partial blockage at the inlet of the inner channel and the impact of corrosion and crud growth are also analyzed by conservertive models. The inner channel can accommodate a blockage of up to 43% of its flow area before MNDBR falls below the 1.3 limit.The crud and ZrO2 buildup does not reduce MDNBR margin below the 1.3 limit, as long as the combined thickness is less than 74[mu]m-94[mu]m. Neutronic analyses are performed for OPR-1000 with both the solid fuel and the annular fuel. The results from an MCNP model of the reference solid fuel assembly and a CASMO-4 model show excellent agreement. The benchmark of annular fuel array shows that CASMO-4 overpredicts the eigenvalues and the slope of the reactivity burnup curve. Fictitiously increasing U-238 number densities in CASMO-4 inputs by 10% produces good match with the MCNP-based burnup code, MCODE2.2. The whole core model of Ulchin Nuclear Unit 5 is established as a benchmark using SIMULATE-3 to calculate the steady state reactor core performance. Last but not least, an equilibrium annular fuel core is proposed, and its steady state core performance is analyzed. The proposed annular fuel assemblies composed of 7.5% and 6.5% U-235 enriched fuel rods, and burnable poisons with various Gd 20 3 weight percentages (4%, 6%, 8%, 10%, and 16%) can satisfy the design targets, such as peak boron concentration, cycle length, and peaking factors in a certain equilibrium loading pattern.

[发布机构] Massachusetts Institute of Technology