Abstract
We use a novel nonintrusive adaptive Reduced Order Modeling method to build a reduced model for a molten salt reactor system. Our approach is based on Proper Orthogonal Decomposition combined with locally adaptive sparse grids. Our reduced model captures the effect of 27 model parameters on keff of the system and the spatial distribution of the neutron flux and salt temperature. The reduced model was tested on 1000 random points. The maximum error in multiplication factor was found to be less than 50 pcm and the maximum L2 error in the flux and temperature were less than 1%. Using 472 snapshots, the reduced model was able to simulate any point within the defined range faster than the high-fidelity model by a factor of 5×106. We then employ the reduced model for uncertainty and sensitivity analysis of the selected parameters on keff and the maximum temperature of the system.
Highlights
Complex systems such as molten salt reactors impose a modeling challenge because of the interaction between multi-physics phenomena
Reduced Order Modeling (ROM) is an effective tool for such applications. This technique is based on recasting the high fidelity, high dimensional model into a simpler, low dimensional model that captures the prominent dynamics of the system with a controlled level of accuracy
The Proper Orthogonal Decomposition (POD) approach is divided into two main phases: the first is the offline phase, where the reduced order model is constructed by solving the high fidelity model at several points in parameter space to obtain a reduced basis space; the second is the online
Summary
Complex systems such as molten salt reactors impose a modeling challenge because of the interaction between multi-physics phenomena (radiation transport, fluid dynamics and heat transfer) Such complex interaction is captured with high-fidelity, coupled models. For practical nuclear reactor applications, the intrusive approach is often challenging because these models are usually implemented with legacy codes that prohibit access to the governing equations, or built with coupled codes that renders modifying the governing equations a complicated task In this case, a nonintrusive approach can be adopted to build a surrogate model for the coefficients of the POD basis. We propose the use of ROM method that combines the nonintrusive POD approach with the sparse grids technique (Bungartz and Griebel, 2004) to build a reduced model of a fastspectrum molten salt system.
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