Abstract
Dual cooled annular fuel is a novel fuel design, which has the potential to improve the reactor power density while maintaining or improving its safety margin. The effects of tight-lattice geometry, fuel burnup, fuel expansion, coolant channel blockage on the thermal hydraulic performance of annular fuel is studied to illustrate its special features in this paper. A sub-channel analysis code named NACAF, which includes empirical constitutive models in consideration of tight-lattice effects on prediction of pressure drop, critical heat flux and turbulent mixing, channel blockage model, heat conduction model for dual surface cooling condition, coolant flowrate distribution between inner and outer channel, is developed for annular fuel assembly or core analysis based on homogenous fluid model. Validation work is carried out with comparing NACAF results with analytical solutions, as well as numerical results of existing sub-channel code for annular fuel, such as VIPRE-01 and TAFIX. Comparison results demonstrates NACAF’s prediction error is acceptable and it has the ability to simulate thermal hydraulic performance of annular fuels or annular fuel bundles. Based on the developed and verified NACAF, the special thermal hydraulic phenomena of annular fuel are studied to clarify the features of annular fuel.
Highlights
The annular fuel concept proposed by MIT can be cooled internally and externally at the same time, which is a new fuel design that can increase power density by more than 30% of its original value and provide higher safety margin (Kazimi and Hejzlar, 2006)
When swelling ratio increases to 40%, the MDNBR will stay lower than 1, which indicates that CHF happens at the outer surface and the outer surface temperature has the risk of sudden increase
The tight-lattice structure like annular fuel assembly can reduce the total pressure by about 20% compared to the results of cylindrical solid fuel assembly
Summary
The annular fuel concept proposed by MIT can be cooled internally and externally at the same time, which is a new fuel design that can increase power density by more than 30% of its original value and provide higher safety margin (Kazimi and Hejzlar, 2006). Description of Study on Tight-Lattice Effect The results calculated by using different correlations (which are suitable to P/D 1.08 and P/D 1.35) are compared to analyze the tight-lattice effect on the turbulent mixing rate, CHF and pressure drop of the annular fuel assembly. The fuel cladding temperature, DNBR, flow and heat split between inner and outer channels under partial blockage conditions at different extent (10, 20, 30, 50, 70 and 80%) are analyzed
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