Abstract
The primary mission of the Versatile Test Reactor (VTR) is to provide peak fast flux in excess of 4.0 x 1015n/cm2-s to support fuel and material testing. To achieve a high fast flux, it is beneficial to maximize the flux peaking in the center of the core. With a single enrichment zone, a highly peaked flux distribution produces a highly peaked power distribution. Coolant inlet orifices can be designed to handle the peaked power distribution but orifice design can be simplified if a more even radial power distribution can be achieved. An approach to reduce the power peaking factor is to use enrichment zoning, which would improve coolant flow homogeneity. Several alternative VTR core configurations are considered with two enrichment zones (15 wt% Pu and 20 wt% Pu). These alternative configurations require more assemblies to maintain reactivity than the reference VTR core, which leads to failure to achieve the design criterion for experimental fast flux with the target core power. Configurations using 20 wt% Pu with different fuel assembly designs having smaller and larger fuel volume fractions are also analyzed. The case having a larger fuel volume fraction reduces the number of fuel assemblies required for criticality, which keeps the experimental flux higher. Configurations with volume fraction zoning can slightly decrease the peaking factor while maintaining the desired fast flux, although some thermal hydraulic limits may not be satisfied. Volume fraction zoning configurations may offer benefits, but determining the feasibility of these configurations requires further thermal hydraulic design and analysis work beyond the scope of the present work.
Highlights
The Versatile Test Reactor (VTR) mission is to enable accelerated testing of advanced reactor fuels and materials required for advanced reactor technologies
There is a constraint on the plutonium content dictated by prior fuel experience and on the uranium enrichment based on existing enrichment capabilities that limits the ultimate performance of the core
These requirements are based on previous Sodium-cooled Fast Reactor (SFR) operating experience with metal fuel, including the Fast Flux Test Facility (FFTF) and Experimental Breeder Reactor II (EBR-II). [3]
Summary
The Versatile Test Reactor (VTR) mission is to enable accelerated testing of advanced reactor fuels and materials required for advanced reactor technologies. Existing Sodium-cooled Fast Reactor (SFR) technology is being leveraged to develop a 300 MWt reactor that provides the desired experimental fast flux. The objective of maximizing the peak fast flux is most achieved by designing a reactor with a large flux gradient. It is possible to effectively cool a reactor with large power peaking ratios using different coolant flow restriction in the core. It is not possible to maintain a constant flow-to-power ratio in all assemblies when large. There could be benefits in reducing the power peaking of the VTR while maintaining the desired experimental fast flux levels. Using multiple fuel enrichments (or fissile fractions) is one of the most effective ways to modify the radial power distribution
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