Local R-Factor Calculation for Boiling Water Reactor Fuel Rods
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Solution Overview
Problem
Existing methods for determining the R-factor in nuclear light water reactors, particularly in boiling water reactors, do not accurately account for the individual properties of fuel rods, leading to inadequate determination of dryout properties and critical power ratios, especially when part-length rods are involved.
Innovation Solution
A method that determines a local R-factor for each fuel rod at multiple axial levels, considering individual axial heat generation profiles, eliminating the need for predetermined weight functions and high additive constants, and calculating a total R-factor for the bundle by maximizing local R-factors at each level, thereby improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If predetermined weight functions and high additive constants are used to determine R-factor, then the calculation process is simplified, but the accuracy of dryout property determination deteriorates
Solution Approach 1:
The patent divides the fuel bundle into multiple axial levels and calculates separate R-factors for each level rather than using a single predetermined weight function. This segmentation allows the calculation to account for local variations in heat generation and coolant flow at different axial positions, improving accuracy while maintaining computational feasibility through systematic breakdown of the problem into discrete segments
Solution Approach 2:
The patent implements local quality by determining specific R-factor values for different axial levels within the fuel bundle. Each level receives a customized R-factor calculation based on its local heat generation rate and neighboring rod conditions, replacing the uniform predetermined weight function approach. This localized treatment captures axial variations in thermal-hydraulic conditions that affect dryout characteristics
2Measurement precision
If individual axial heat generation profiles are considered for each fuel rod, then the determination accuracy of R-factor is improved, but the computational complexity increases
Solution Approach 1:
The patent manages computational complexity by segmenting the fuel bundle into a finite number of axial levels and calculating R-factors at each discrete level. This approach transforms the continuous problem into a discrete set of calculations, making the computation tractable while still capturing the essential axial variations in heat generation and thermal-hydraulic conditions
Solution Approach 2:
The patent applies partial action by selecting a representative number of axial levels (not every possible point) to calculate R-factors. This selective sampling provides sufficient accuracy for dryout determination without requiring exhaustive computation at every axial position, balancing precision with computational efficiency
3Adaptability or versatility
If part-length rods are included in the fuel bundle, then the operational flexibility is improved, but the accuracy of dryout margin determination deteriorates due to inadequate compensation methods
Solution Approach 1:
The patent addresses part-length rods through local quality by calculating specific R-factor values at each axial level where the part-length rods are present. Rather than applying blanket compensation constants, the method computes localized R-factors that reflect the actual thermal conditions at each level, naturally accounting for the reduced heat generation from shorter rods without requiring arbitrary compensation factors
Solution Approach 2:
The patent employs parameter changes by allowing the R-factor to vary axially through different calculated values at different levels. This dynamic parameter approach replaces static compensation constants with computed values that adapt to the specific configuration of part-length rods, capturing their actual thermal impact on neighboring rods and improving dryout margin determination accuracy
Data Source
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AI summary
The present invention concerns a method of determining the R-factor for a bundle of nuclear fuel rods in a nuclear light water reactor of the boiling water reactor kind. The R-factor is a factor that accounts for the weighted local power influence on a fuel rod. A local R-factor (Ri(z)) is determined for each fuel rod (i) in said bundle and for each of a plurality of levels (z) in an axial direction. The individual axial heat generation profile for a certain fuel rod (i) is taken into account when determining the local R-factors (Ri(z)) for said fuel rod (i). The invention also concerns a processor configured for automatically determining the R-factor, a computer program product, a method of determining the critical power for a bundle of fuel rods, a nuclear energy plant, and a method of operating a nuclear energy plant.