Core Shroud Removal via Ceiling Opening and Segmentation
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Solution Overview
Problem
Current methods for removing a core shroud in a boiling water reactor nuclear power plant are time-consuming and pose safety risks due to the need for multiple cutting steps and the potential for the shroud to fall into fuel storage pools during removal.
Innovation Solution
A method involving forming an opening in the reactor building ceiling above the equipment pool, cutting the core shroud in one axial position, surrounding it with a radiation shield, and removing it through this opening to prevent falling into fuel storage pools, thereby reducing the time and enhancing safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the core shroud is coarsely cut up in the RPV and then further cut into finer pieces in a reactor well, then the core shroud can be removed, but the process takes long time due to two cutting steps
Solution Approach 1:
The core shroud is segmented into multiple sections by cutting it at multiple positions along its length. These segmented sections can then be handled and removed separately, reducing the complexity and time of the removal process compared to handling the entire shroud as one piece.
Solution Approach 2:
A carrying device is introduced as an intermediary tool to hold and transport the cut sections of the core shroud from the reactor well to the storage pool. This intermediary device streamlines the transfer process and eliminates the need for complex manual handling operations.
2Productivity
If the core shroud is carried out through an opening portion in the ceiling, then the removal time is reduced, but there is a safety risk that the shroud may fall into the fuel storage pool
Solution Approach 1:
A carrying device serves as an intermediary between the core shroud sections and the storage pool, providing a controlled and safe transfer mechanism. This device prevents direct dropping or uncontrolled movement of the shroud sections into the fuel storage pool while still enabling efficient removal through the ceiling opening.
Solution Approach 2:
The carrying device is designed with safety features that prevent the core shroud sections from falling into the fuel storage pool. These preventive measures are built into the device structure, ensuring safety before any potential accident can occur, rather than relying on corrective actions after a problem arises.
3Reliability
If fuel assemblies are transferred to another storage pool to prevent damage from falling shroud, then safety is improved, but the time required for carry operation increases
Solution Approach 1:
The carrying device acts as an intermediary protection mechanism that safeguards fuel assemblies without requiring their relocation. By providing a controlled transfer path that prevents the core shroud from falling into the storage pool, the device eliminates the need for time-consuming fuel assembly transfers to other pools.
4Reliability
If protection devices are set up in the reactor well to prevent shroud upset, then safety is improved, but the complexity and time of the operation increases
Solution Approach 1:
The carrying device is a simpler intermediary solution compared to complex protection devices that would need to be set up in the reactor well. It provides the necessary safety function of preventing shroud upset and fuel pool contamination through a more straightforward design that reduces operational complexity.
Data Source
AI summary
A method for carrying out a reactor internal, comprising steps of:forming a first opening portion in a ceiling of a reactor building at a position directly above an equipment pool in said reactor building;cutting a cylindrical reactor internal surrounding a core in a reactor pressure vessel disposed in said reactor building, at one position in an axial direction;surrounding said cut cylindrical reactor internal with a radiation shield; andcarrying out said cylindrical reactor internal surrounded by said radiation shield out of said reactor building through said first opening portion.