Looking for Cracks in Control Rod Drive Mechanisms (CRDM)
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The document discusses the challenges and solutions for inspecting control rod drive mechanisms (CRDM) in nuclear reactors, focusing on the difficulties of accessing tight spaces and detecting internal cracks. It presents a newly designed probe that can collapse and expand to fit into a narrow gap while providing high-quality signals for defect detection. This innovative solution enhances inspection capabilities, allowing for the identification of previously uninspected areas and improving overall safety in nuclear power operations.
Looking for Cracks in Control Rod Drive Mechanisms (CRDM)
- 1. Inspecting for Cracks in Tight Places Application Note
- 2. The Challenge Control rod drive mechanisms (CRDM): • Located above nuclear reactor vessels • CRDMs insert, hold, lift control rods • Used to stop nuclear reaction CDRMs are essential to safe operation of nuclear power plants. 2 © Eddyfi NDT Inc. 2009–2015
- 3. The Challenge CRDM penetration nozzles: • Penetrate into reactor vessel head • Subject to various stresses: • Axially oriented ID cracking • Surface-breaking flaws typical • Depth = 1.0–1.5 mm (0.039–0.059 in) • Length = 5.0–5.2 mm (0.197–0.205 in) • Some stress-corrosion cracking and subsurface cracking 3 © Eddyfi NDT Inc. 2009–2015
- 4. The Challenge • Can only be inspected from inside reactor vessel: inspection must be robotized • Penetration nozzle geometry • At nozzle mouth, ±12 mm (0.472 in) gap between nozzle ID and thermal sleeve • Nozzle tapers around sleeve: gap 2 mm (0.079 in) 4 © Eddyfi NDT Inc. 2009–2015
- 5. The Challenge • Current probe: • Able to inspect wider diameter portion • Cannot fit into 2 mm gap • Potential solution must adapt to geometry variation • Reactor vessel head and thermal sleeve made of austenitic alloys: • Corrosion and oxidation resistant • Magnetic properties unique challenge for electromagnetic inspection: • Cracks at the ID must be detected, but unwanted interference from thermal sleeve must also be eliminated to leave only indications from at the ID. 5 © Eddyfi NDT Inc. 2009–2015
- 6. The Solution • Solution both simple and elegant • As illustrated, probe head collapses and expands around thermal sleeve so probe fits in 2 mm (0.079 in) space 6 © Eddyfi NDT Inc. 2009–2015
- 7. The Solution • Probe head made of finely machined technical thermoplastic: • Achieves collapsibility • Enough pressure on probe head • Keeps contact with the nozzle’s ID constant • Machined technical thermoplastic: • Extremely durable • Flexible • Can reshape • Avoids moving parts 7 © Eddyfi NDT Inc. 2009–2015
- 8. The Solution 8 © Eddyfi NDT Inc. 2009–2015 • Inside probe head: • ECT coils shielded from thermal sleeve interference by highly conductive alloy that produces clear signals from nozzle ID • No need for bulky external multiplexer • Ingeniously designed setup file • 4× transmit-receive channels • 1× absolute channel • Five topologies: • Axial long single drive: Detects axial defects • Axial short dual driver: Detects small axial defects • Circumferential long single driver: Detects circumferential defects • Circumferential short single driver: Detects small axial defects • 1× absolute channel used to monitor liftoff
- 9. The Solution 9 © Eddyfi NDT Inc. 2009–2015 Inspection results rendered as Lissajous and C-scans for easy interpretation Axial scan results on calibration standard
- 10. The Solution 10 © Eddyfi NDT Inc. 2009–2015 Calibration results demonstrate the probe is capable of detecting with the axial topologies: • FBH • Diameter: 1.37 mm (0.054 in) • Depth: 1 mm (0.039 in) • EDM notch • Length: 5.08 mm (0.200 in) • Width: 0.10 mm (0.004 in) • Depth: 0.25 mm (0.010 in) • Angle: 0°
- 11. The Solution 11 © Eddyfi NDT Inc. 2009–2015 With circumferential topologies, probe capable of detecting: Circumferential scan results on calibration standard • FBH • Diameter: 1.37 mm (0.054 in) • Depth: 1 mm (0.039 in) • EDM notch • Length: 5.16 mm (0.203 in) • Width: 0.10 mm (0.004 in) • Depth: 0.51 mm (0.020 in) • Angle: 90°
- 12. The Benefits • Inspection of previously uninspected areas and increased security • The design adapts to the small available space to discover previously undetected defects. • More sensitivity and detail • More topologies yield more information and a higher level of details in scans, which enables detecting and sizing smaller defects. • Signal quality • The shielding in the probe head returns high-quality, interference-free indications. 12 © Eddyfi NDT Inc. 2009–2015
- 13. www.eddyfi.com