Gray Control Rod with Terbium Dysprosium Neutron Absorber
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Solution Overview
Problem
The gray control rod assemblies in nuclear power plants face rapid reactivity worth decline due to fuel consumption, leading to reduced controlling ability and safety issues, as existing materials like Ag—In—Cd alloy experience significant neutron absorption cross section decreases, necessitating frequent replacements and potential power distribution unevenness.
Innovation Solution
Incorporating a neutron absorber with a first component (e.g., metal terbium or its alloys) whose reactivity worth increases over time and a second component (e.g., metal dysprosium or its alloys) whose reactivity worth decreases, maintaining a stable reactivity worth within 15% variation over 20 years, using Dy—Tb alloy rods with specific mass fractions and diameters to achieve a planar reactivity worth loss characteristic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional neutron absorber materials (Ag-In-Cd alloy, Hf, Dy) are used in gray control rods, then the initial reactivity worth can be achieved, but the reactivity worth declines rapidly over time due to fuel consumption
Solution Approach 1:
The patent applies parameter changes by selecting specific isotopic compositions (e.g., Hf-179 content between 5-30%, Er-166 content between 5-30%) to optimize the balance between initial reactivity worth and long-term stability. By adjusting these isotopic parameters, the control rod maintains effective reactivity control throughout its service life while minimizing rapid decline
Solution Approach 2:
The patent uses composite neutron absorber materials combining multiple elements (Hafnium and Erbium, or Terbium and Dysprosium) with specific isotopic ratios. This composite approach leverages the complementary characteristics of each element: Hf-179 and Er-166 (or Tb-159 and Dy-164) have increasing reactivity worth over time, compensating for the declining reactivity of other components, thereby extending the control rod's effective service life
2Quantity of substance
If the neutron absorber diameter is reduced to achieve lower initial reactivity worth, then the gray control rod can be used for load tracking, but the self-shielding effect decreases leading to faster reactivity decline
Solution Approach 1:
The patent changes the isotopic composition parameters of the neutron absorber material to achieve the desired reactivity worth without reducing diameter. By optimizing isotopic content (e.g., Hf-179 between 5-30%, Er-166 between 5-30%), the material provides appropriate initial reactivity while maintaining longer service life through reduced self-shielding effects
3Reliability
If Ag-In-Cd alloy is used as neutron absorber, then good initial neutron absorption is achieved, but significant volume expansion occurs after irradiation leading to cladding tube rupture
Solution Approach 1:
The patent extracts Cadmium from the Ag-In-Cd alloy formulation and replaces it with alternative neutron absorber materials (Hafnium, Erbium, or Terbium-Dysprosium combinations). This extraction eliminates the volume expansion problem associated with Cd transmutation products while maintaining effective neutron absorption capabilities through the selected alternative materials
Solution Approach 2:
The patent employs composite materials (Hf-Er or Tb-Dy combinations) that provide equivalent or superior neutron absorption to Ag-In-Cd alloy without the harmful volume expansion effect. These composite materials offer improved dimensional stability under irradiation, preventing cladding tube rupture while maintaining reliable neutron absorption
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly enhances the maximum reactivity worth of gray control rod assemblies, reduces wear, and extends their life, while maintaining safety by minimizing the risk of power distribution issues and cladding tube failure, offering a more stable and efficient reactivity control.
Implementation Method 1
elements in the neutron absorber of the gray control rod will be consumed and transmuted along with the fuel consumption
Implementation Method 2
elements in the neutron absorber of the gray control rod will be consumed and transmuted along with the fuel consumption
Data Source
AI summary
A gray control rod having a neutron absorber comprising terbium and dysprosium is provided. The neutron absorber comprises at least one first component and at least one second component, the reactivity worth of the first component increases as the service time of the neutron absorber increases, the reactivity worth of the second component decreases as the service time of the neutron absorber increases; the reactivity worth of the neutron absorber varying no more than 15% within the service time of the neutron absorber. By using the first component and the second component to form the neutron absorber, and adjusting the proportion of the respective components in the neutron absorber, the neutron absorber having a substantially planar reactivity worth loss characteristic can be obtained. The gray control rod and the assembly having required reactivity controlling ability can be obtained by increasing or decreasing the material dosage of the neutron absorber.