Jet Pump Diffuser Weld Repair Device
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Solution Overview
Problem
Cracked welds in jet pump diffuser assemblies of boiling water reactor (BWR) power plants, particularly at the Alloy 600 to stainless steel transitions, lead to potential detachment of diffusers, disrupting recirculation flow and posing risks during LOCA accidents, with existing repair methods being limited and not thoroughly tested.
Innovation Solution
A remotely installable jet pump diffuser weld repair device featuring lower and upper ring sections with gripper slots and cam surfaces, secured by connector bolts, which provide radial inward force to engage with machined pockets on the diffuser, offering structural support and accommodating thermal expansion differences between materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tie rod assembly repair method is used, then jet pump diffuser weld cracks can be repaired, but the scope of repair is limited and full scale mockup testing was not done
Solution Approach 1:
The repair device is divided into multiple segments including upper and lower clamp rings, gripper assemblies, and connector bolts that can be independently installed and positioned. This segmentation allows the repair device to be assembled in the limited space of the shroud to vessel annulus and enables modular replacement or adjustment of individual components.
Solution Approach 2:
The gripper assemblies are nested within the clamp rings, with gripper slots integrated into the ring structures. The connector bolts pass through both the upper and lower clamp rings to secure them together. This nested configuration reduces the overall device footprint and allows compact installation in the confined reactor space.
2Reliability
If repair clamps are installed in the limited space in the shroud to vessel annulus, then weld cracks can be repaired, but installation and operation space is constrained
Solution Approach 1:
The clamp is segmented into upper and lower rings that can be positioned independently around the diffuser assembly. This allows the repair device to be installed in the confined annular space by placing each ring segment separately and then connecting them with bolts, rather than requiring installation of a single large clamp.
Solution Approach 2:
The repair device utilizes the circumferential dimension by positioning clamp rings around the diffuser assembly rather than requiring linear space. The gripper slots are arranged radially to engage with the diffuser outer surface, effectively using the radial dimension to provide repair capability without occupying excessive axial or lateral space.
3Strength
If connector bolts are used to draw lower and upper ring sections together, then structural support is provided, but stress and vibration criteria must be met
Solution Approach 1:
The cam surfaces are located specifically at the gripper-diffuser interface points rather than distributing force uniformly around the entire clamp. This concentrates the gripping force at localized contact points where the grippers engage the diffuser outer surface, providing effective structural support while allowing the clamp structure itself to flex and accommodate thermal expansion without generating excessive stress.
Solution Approach 2:
The cam surfaces enable the grippers to dynamically adjust their engagement with the diffuser assembly. As the lower and upper ring sections are drawn together by connector bolts, the cam surfaces convert the axial bolt force into radial gripping force that can accommodate variations in diffuser geometry and thermal expansion, maintaining reliable contact under varying operational conditions.
4Ease of operation
If the repair device is remotely installable, then installation can be performed in confined reactor space, but device design complexity increases
Solution Approach 1:
The device is segmented into modular components (upper ring, lower ring, gripper assemblies, connector bolts) that can be independently handled and installed by remote tools or personnel working in the confined annular space. Each segment is designed to be manageable in size and can be positioned separately before final assembly.
Solution Approach 2:
The clamp rings serve multiple functions: they provide structural support for the diffuser assembly, house the gripper slots for engagement with the diffuser outer surface, and act as mounting structures for the connector bolts. This multi-functionality reduces the number of separate components needed, simplifying the overall device design while maintaining remote installability.
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 repair device ensures the integrity of the diffuser assembly, allowing for safe shutdown conditions during failures, with a 40-year design life and no adverse impact on jet pump operation, avoiding the need for machining holes in the shroud support plate and meeting stress and vibration criteria.
Implementation Method 1
at least one of the gripper slots and the grippers defines cam surfaces shaped to drive the grippers radially inward as the lower and upper ring sections are drawn toward each other
Implementation Method 2
A plurality of connector bolts are secured between the lower ring section and the upper ring section. Tightening the connector bolts draws the lower and upper ring sections toward each other.
Data Source
AI summary
A jet pump diffuser weld repair device includes a lower ring section and an upper ring section respectively sized to fit around a circumference of the diffuser on opposite sides of the weld to be repaired. The lower and upper ring sections are provided with a plurality of aligned gripper slots. A corresponding plurality of grippers are fit into the gripper slots, where at least one of the gripper slots and the grippers defines cam surfaces shaped to drive the grippers radially inward as lower and upper ring sections are drawn toward each other. A plurality of connector bolts are secured between the lower ring section and the upper ring section. Tightening of the connector bolts draws the lower and upper ring sections toward each other.