Nuclear Reactor Decontamination Using Dilute EDTA Citric Acid
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Solution Overview
Problem
Current decontamination processes for nuclear reactors, such as CAN-DECON™ and CAN-DEREM™, are inefficient in high oxide and radionuclide loadings, requiring longer times and causing corrosion in stainless steel systems, and are not suitable for Pressurized Heavy Water Reactors (PHWRs) and certain types of piping.
Innovation Solution
A dilute decontamination reagent composition of 0.6 to 3.0 g/L EDTA and 0.4 to 2.2 g/L citric acid is used, avoiding oxalic acid to prevent corrosion and iron oxalate precipitation, injected as a slurry into the reactor system, with a regenerative process involving cation and mixed bed ion exchange resins for efficient radionuclide removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional decontamination reagents (oxalic acid, EDTA, citric acid) are used to dissolve radionuclides and oxides, then decontamination effectiveness is improved, but corrosion of stainless steel surfaces occurs and iron oxalate precipitation forms
Solution Approach 1:
The patent removes oxalic acid from the decontamination reagent formulation, extracting the harmful component that causes corrosion and iron oxalate precipitation. The reagent now consists only of EDTA and citric acid, eliminating the source of the harmful oxalate ions while maintaining decontamination capability through the remaining chelating agents.
Solution Approach 2:
The patent changes the chemical composition parameters of the decontamination reagent by eliminating oxalic acid and specifying precise concentration ranges for EDTA (0.02-0.1 M) and citric acid (0.05-0.2 M). This parameter modification resolves the contradiction by maintaining effective chelation while removing the corrosive and precipitating effects of oxalate.
2Reliability
If concentrated reagents are used for decontamination, then dissolution of metal oxides and radionuclides is enhanced, but the process time increases and system shut-down time is extended
Solution Approach 1:
The patent optimizes the concentration parameters of the decontamination reagent to achieve the best balance between dissolution efficiency and process time. By specifying optimal ranges for EDTA (0.02-0.1 M) and citric acid (0.05-0.2 M), the reagent achieves effective decontamination in reduced time without requiring excessively high concentrations that would extend processing.
Solution Approach 2:
The patent implements a continuous circulation process where the decontamination reagent is continuously pumped through the reactor coolant system, ensuring sustained contact with contaminated surfaces. This continuous action maximizes dissolution efficiency within the available time frame and allows for more effective use of the reagent compared to batch processing.
3Reliability
If existing decontamination processes are applied to PHWRs with high oxide and radionuclide loadings, then some contamination is removed, but the process is inefficient and requires extended time
Solution Approach 1:
The patent uses a composite decontamination reagent system combining EDTA and citric acid in specific proportions. This composite formulation leverages the complementary chelating properties of both agents to effectively handle high oxide and radionuclide loadings in PHWRs, achieving superior decontamination rates compared to single-agent systems or conventional formulations.
Solution Approach 2:
The patent optimizes the concentration ratio and absolute concentrations of EDTA and citric acid to specifically address high loading conditions in PHWRs. The specified ranges (EDTA: 0.02-0.1 M, citric acid: 0.05-0.2 M) are tuned to maximize the decontamination rate for heavy oxide deposits and radionuclide accumulations typical of pressurized heavy water reactors.
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
The process achieves a higher Decontamination Factor (DF) in shorter times, reducing shut-down times and avoiding corrosion, making it effective for both carbon steel and stainless steel reactors with high oxide and radionuclide loadings.
Implementation Method 1
A decomtaminating reagent mixture comprising from about 0.6 to about 3.0 g/L (2.1-10.3 mM) EDTA and from about 0.4 to about 2.2 g/L (2.1-11.5 mM) citric acid
Implementation Method 2
a decontaminating reagent mixture comprising from about 0.6 to about 3.0 g/L (2.1-10.3 mM) EDTA and from about 0.4 to about 2.2 g/L (2.1-11.5 mM) citric acid
Implementation Method 3
The dilute reagent solution is circulated to dissolve the deposits and then passed through a cation exchange resin to collect dissolved cations and radionuclides
Implementation Method 4
the acidic reagents are removed by contact with an anion exchange resin to restore the coolant to its original condition
Data Source
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AI summary
The present application is related to a concentrated decontaminating reagent composition and related method useful for decontamination of nuclear reactors, or components thereof. The concentrated reagent composition is injected into the nuclear reactor, or component thereof, to form a dilute reagent that comprises from about 0.6 to about 3.0 g/L (2.1-10.3 mM) EDTA and from about 0.4 to about 2.2 g/L (2.1-11.5 mM) citric acid. The composition and method of this application can be used effectively in a regenerative process to decontaminate a nuclear reactor, or a component of thereof, with high efficiency without causing significant corrosion to the components of the cooling systems.