Abstract
In coupled multiphysics simulations, single pin-averaged values are typically used to describe the temperature, power, and burnup within a given fuel pin. However, since xenon oscillations are largely driven by fuel temperatures, radially dependent quantities have been implemented in the Virtual Environment for Reactor Applications. These radial-shaping functions are based on Zernike polynomial expansions and allow information to pass effectively between codes with differing spatial meshes. This work examines the effects of radial fuel temperature-shaping functions on the behavior of axial xenon oscillations. A test problem was developed from full-core, multi-cycle depletions using as-built fuel data. The center 25 assemblies of the full-core case were used to test the radial-shaping function by inducing an axial xenon oscillation using an instantaneous control rod movement. The test case was run with and without the radial shapes, and each component was also run individually. Including the shaping functions significantly impacted the xenon oscillations for this problem; the magnitude and period of the oscillations were altered, and large pin power and soluble boron differences were observed. Testing each component individually showed that the radial fuel temperature-shaping function had the largest effect.
Highlights
Predicting reactor behavior through modeling and simulation depends greatly on the ability to capture the effects of coupled sets of physics
Using the methodologies described in the previous section, five different xenon oscillation cases were examined
The final three cases had the burnup, power, and temperature radial coupling shapes enabled independently from each other to determine their individual impacts on the problem
Summary
Predicting reactor behavior through modeling and simulation depends greatly on the ability to capture the effects of coupled sets of physics. The phenomenon of axial power oscillations due to xenon buildup, near the end of a fuel cycle, is of interest to reactor designers and operators. Advanced modeling and simulation tools struggle to accurately predict xenon oscillations due to the complex multiphysics nature of the problem. In CASL, it is important to model these axial power oscillations to better quantify the fuel duty during normal end of life operations and load-following scenarios. Avoidance can increase person time in power maneuver planning and, at worst, could result in reduced electrical output. To better capture these effects during multiphysics simulations, Zernike polynomials were used to describe the radial pin temperature, power, and burnup shapes. The following subsections provide the necessary background on these topics
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