Earlier MIT studies have shown that internally and externally cooled annular fuel makes it possible to significantly increase (by up to 50%) power density in the standard Westinghouse PWR while maintaining or increasing safety margin. The present project has evaluated feasibility of 20% higher power density for the Korean OPR-1000 reactor having annular fuel assemblies of different dimensions and operating conditions than the standard Westinghouse PWR used in previous MIT analyses. The most important difference is keeping the coolant flow rate fixed at the reference value in this study. (H/T Charles Barton
DNBR evaluation of an annular fueled core using VIPRE-01 for the whole core showed that the original KAERI annular fuel design has larger MDNBR margin than the solid fuel at 100% power. Assuming an unchanged core flow rate and equal conductances for the inner and outer gaps, however, this design cannot achieve power uprate to 120% even with a reduced core inlet temperature. The MDNBR in the inner channel is too small. This problem arises because the diameter of the inner channel does not allow sufficient flow rate through it. Use of KAERIs suggested gap conductances (3500/7000 for inner/outer) significantly alleviates this problem, allowing an uprate to 117.55%. Search was then performed to identify a better optimized design that could achieve 20% power uprate. This might be accomplished through fine-tuning of the rod dimensions by slightly increasing both inner channel and outer channel diameters, while keeping the fuel to moderator ratio fixed, but the modified design requires reducing the gap between the rods to 1mm, which may challenge manufacturing feasibility. An alternative design with slightly larger gap was shown to also achieve 120% power with good MDNBR margin, but requires grids with higher grid loss coefficient and results in a slight increase of core pressure drop.
Core physics parameters of an equilibrium core for an OPR-1000 type reactor with annular fuel were found to be similar to those of a solid pellet core, even with a 20% uprate. This suggests that reactor physics considerations peculiar to annular fuel do not provide any impediment to its use. The proposed annular fuel assemblies are composed of 7.5% and 6.5% U-235 enriched fuel rods, and burnable poisons with various Gd2O3 weight percentages ranging from 4% to 16%.
The annular fuel design given by KAERI exhibits a better performance than the solid rod because it is capable of achieving 70 MWd/kg burnup at both 100% and 120% power.
the largest possible power uprate that appears justifiable from the present study is 17.55% for the 12x12 annular fuel, close to but still less than the target of 20%. This limit arises largely from DNB considerations in the inner channel of the annular fuel. However, given that our analyses have applied conservative assumptions to cover the transient effects and uncertainties, and that our methods have not been calibrated as much for the Korean reference assembly designs (like grid effects, and power distribution factors), this 2.45% difference in the uprate level may simply amount to added conservatism.
Other Nuclear Uprates
The Shaw Group Inc. announced it has been awarded a contract with Entergy Operation, Inc., a subsidiary of Entergy Corporation to provide an extended power uprate (EPU) plant modifications at Grand Gulf Nuclear Station in Port Gibson, Miss.
Shaw will provide engineering, procurement and construction services designed to add approximately 178 megawatts of power generation to Grand Gulf Nuclear Station. Engineering and procurement are underway with construction to follow to install plant modifications in spring 2012.
The number of extended nuclear plant uprates is increasing
Industrial Info is tracking 18 nuclear uprate projects, which have a combined total investment value of more than $3.9 billion
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