Radioactive Waste Evaporation to Prevent Barium Nitrate Crystallization
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Solution Overview
Problem
Existing methods for concentrating highly active radioactive waste from nuclear fuel reprocessing face challenges such as impurity sedimentation, explosion hazards, and inefficiencies in nitric acid decomposition, particularly when using formaldehyde as a reducing agent, which limits the safety and efficiency of the evaporation process.
Innovation Solution
A method involving the use of a mixture of formaldehyde and formic acid as a reducing agent in a continuous evaporation process, with a controlled aging period and reduced formaldehyde concentration, to achieve safe and efficient nitric acid decomposition without forming nitrous oxide, thereby preventing barium nitrate crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If formaldehyde is used as a reducing agent in high concentration to ensure efficient nitric acid decomposition, then the decomposition efficiency is improved, but fire and explosion hazards increase
Solution Approach 1:
The patent changes the concentration parameter of formaldehyde from high (6.5 moles/L) to low (0.65-2.0 moles/L), and introduces formic acid as an additional reducing agent. This parameter change maintains nitric acid decomposition efficiency while reducing fire and explosion hazards by more than 10 times.
Solution Approach 2:
The patent uses a composite reducing agent system combining formaldehyde and formic acid in specific molar ratios (1:2 to 1:5). This composite approach allows the system to maintain effective nitric acid decomposition while the formic acid component suppresses nitrous oxide formation and reduces overall fire hazards.
2Productivity
If conventional evaporation methods are used to concentrate highly active raffinate, then nitric acid regeneration is achieved, but barium nitrate sediment clogs the circulation pipe
Solution Approach 1:
The patent converts the harmful effect of barium nitrate precipitation into a beneficial control mechanism. By carefully controlling nitric acid concentration through the reducing agent system, barium nitrate remains in solution during evaporation and is only precipitated in the final concentrated product, preventing clogging while achieving concentration goals.
Solution Approach 2:
The patent changes the nitric acid concentration parameter throughout the evaporation process by using formaldehyde-formic acid as reducing agents. This maintains nitric acid concentration below the barium nitrate precipitation threshold during the evaporation phase, preventing sediment formation and pipe clogging.
3Object-affected harmful factors
If formaldehyde concentration is reduced to improve fire safety, then fire hazards are decreased, but nitric acid decomposition efficiency may be compromised
Solution Approach 1:
The patent employs a composite reducing agent system where formic acid complements formaldehyde. The formic acid component has high reducing efficiency and suppresses nitrous oxide formation, allowing the system to maintain effective nitric acid decomposition even at low formaldehyde concentrations, thus preserving productivity while improving safety.
Solution Approach 2:
Formic acid acts as an intermediary reducing agent that bridges the gap between safety requirements and decomposition efficiency. It provides the necessary reducing capability at low concentrations where formaldehyde alone would be insufficient, while also suppressing harmful nitrous oxide formation.
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 method ensures safe and efficient evaporation of radioactive waste by reducing formaldehyde concentration up to 10 times, maintaining nitric acid balance, and preventing barium nitrate precipitation, thus enhancing fire safety and process stability.
Implementation Method 1
use of a mixture of formaldehyde and formic acid as a reducing agent in a continuous evaporation process, to achieve safe and efficient nitric acid decomposition
Implementation Method 2
continuous evaporation of a solution, as fed to a bottom part of a circulation-type evaporator
Implementation Method 3
evaporation operations are usually carried out in an evaporator having an external heating chamber and natural circulation of the bottoms solution
Data Source
AI summary
The present disclosure relates to nuclear chemical, particularly radiochemical, technologies at different stages of the nuclear fuel cycle, such as the production of purified nuclear materials (uranium, zirconium) or the reprocessing of spent nuclear fuel from nuclear power stations, in which extraction processes and operations for purifying nuclear materials are used. An example method, which includes the partial decomposition of nitric acid during continuous evaporation while a solution containing a reducing agent is fed into the bottom part of an evaporator having a circulating bottoms solution, consists in that the process is carried out such that the solution is kept in the bottom part of the evaporator for more than 2 hours under the addition of an aqueous solution of formaldehyde and formic acid (hereinafter “the mixture”) or a solution of formic acid after the process has been started using the mixture.