Heavy Water Reactor Calandria Dismantling via Segmented Extraction
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Solution Overview
Problem
The dismantling of heavy water reactor facilities poses a risk of worker exposure and radiation leakage due to the highly radioactive nature of the calandria and calandria vault structures.
Innovation Solution
A methodical dismantling process involving the draining of coolants and moderators, decontamination, and controlled removal of components such as reactor pipes, cover assemblies, and internal structures, utilizing transfer devices and cutting means to safely extract the calandria and calandria vault, minimizing worker exposure and facilitating remote control operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the calandria and calandria vault are dismantled using conventional methods, then the dismantling process can be completed, but worker exposure to radiation and radiation leakage risk increase
Solution Approach 1:
The dismantling process is divided into distinct sequential stages: preparation (draining coolants/moderators, decontamination), cover assembly removal, calandria extraction, and calandria vault dismantling. This segmentation allows for controlled progression through each phase with appropriate safety measures at each step, reducing overall radiation exposure risk to workers
Solution Approach 2:
Before the actual dismantling of radioactive structures, preliminary actions are performed including draining all coolants and moderators from the calandria, decontaminating the calandria and pressure tubes, and drying the calandria. These preliminary steps reduce radioactivity levels and eliminate radiation hazards before workers or equipment approach the structures
Solution Approach 3:
Transfer devices are introduced as intermediaries to handle the calandria during extraction. The transfer device inserts into the calandria vault through the upper portion and provides a mechanical interface for safe removal of the calandria, allowing remote or automated operation that minimizes direct worker exposure to radiation
2Ease of operation
If the calandria is dismantled by cutting between main shell and sub shell, then the calandria can be extracted, but the complexity of the dismantling process increases
Solution Approach 1:
The calandria structure itself is segmented into main shell and sub shell portions that can be separated by cutting. This structural segmentation allows the calandria to be divided into manageable sections for extraction, with the cutting operation creating separable joints that facilitate removal through the calandria vault
Solution Approach 2:
A transfer device serves as an intermediary mechanism that inserts into the calandria vault and provides the mechanical means for both the cutting operation and subsequent extraction. This single intermediary device consolidates multiple functions (positioning, cutting, supporting, and extracting) into one system, managing the overall complexity rather than requiring separate equipment for each operation
Data Source
AI summary
A radioactive structure dismantling method of a heavy water reactor facility that includes a calandria including a main shell and a sub shell, a calandria vault that receives the calandria therein, and a cover assembly that covers the calandria according to an embodiment, includes: preparing dismantling of the calandria; dismantling a reactor pipe installed in the calandria; dismantling the cover assembly that covers the calandria; dismantling the calandria; and dismantling the calandria vault.