Reduce Scheduling Cost, Dose, and Waste in Inspection of Steam Generator Tubing Using an Enhanced Bobbin Eddy Current Coil Inspection Technique - MTA-MA-016

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Administrative Items
Date	12/15/2020
Functional Area Where Benefits Will Be Realized	Maintenance Engineering Quality Control
Reference Implementation Guidance	2017 TIP Award Enhanced Steam Generator Tube Foreign Object Wear Detection Using the Bobbin Eddy Current Coil (ID: 10107950) Steam Generator Management Program: Pressurized Water Reactor Steam Generator Examination Guidelines: Revision 8 (EPRI 3002007572) Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines, Revision 5 (EPRI 3002020909)
Industry SME	EPRI – SGMP Contact: NuclearPlantMod@epri.com
Previous Implementation	Please contact EPRI for implementation examples and contacts.
Implementation Enablers	N/A
Applicability	Applicable to nuclear plants with steam generators Applicable to all geographic regions
Keywords	Steam generator inspection; eddy current; bobbin probe; supplemental probe; degradation detection
Business Case Analysis Cross-Reference	N/A

Description

Eddy current examination of steam generator tubing is performed to detect flaws such as corrosion, pitting, cracks, and erosion. A bobbin eddy current inspection probe made of conductive coils is excited with an electric current to produce an alternating magnetic field, inducing an electric current in nearby conductive materials (known as eddy currents). Defects on the surface or within the tubing material cause changes in the phase and amplitude of the eddy current. Typical methods of bobbin probe examination have difficulty detecting foreign object‑induced wear at geometric changes of tubing, specifically near the tubesheet transition region, requiring a supplemental probe to complete the inspection. Use of a supplemental probe in this transition region represents a significant portion of the inspection cost while foreign object wear at this location typically affects a very small number of tubes at any given inspection.

An enhanced bobbin current coil inspection technique uses mixing of high, mid, and low frequencies (“ALFS” mixes) to improve the bobbin coils’ detection capabilities for foreign object wear at the tubesheet transition region. The technique is qualified up to a specific three‑frequency mix noise level. This threshold is plant specific and is a function of the steam generator design and operating conditions. For tubes which exhibit three‑frequency noise exceeding this threshold, inspection is performed using a supplemental probe. Analysis of the three‑frequency mix channel technique data can be accomplished by manual analysis or by using computer‑based compare programs. This technique reduces the supplemental probe scope, in some applications by 90 % to 95 %, and, therefore, results in improved outage schedules, personnel safety, and overall outage costs.

Benefits

Benefits Estimate

Level 1 – Savings are less than $1 million per year. Savings are estimated to be between $200,000‑500,000 per outage based on previous implementations. Savings are driven by the size of the steam generator and the tubing material.

Benefits Description

• Reduction in personnel dose because fewer supplemental probe examinations are required (Palo Verde saw an 85% reduction in supplemental probe use and Braidwood saw a 66% reduction).
• Reduction in contaminated solid waste because fewer supplemental probe change‑outs are required.
• Improved outage scheduling by limiting the extent of supplemental probe inspections.
• Reduction in human error associated with changing analysis methods between the bobbin probe and supplemental probe.

Costs and Schedule

Cost

Level 3 – Implementation cost of the three‑frequency mix channel technique with the steam generator inspection compare software is less than $1 million. Depending on the plant’s current analysis software, the costs associated with outage inspection data preparation and quantification may already be included. If not, data preparation and quantification costs are approximately $100,000 per unit per outage. Purchase of the compare software from the vendor costs approximately $50,000 (see Previous Implementation for vendor options).

Schedule

Less than six months.

Scope Context

Per unit. Cost and schedule estimates are driven by outage inspection data preparation and implementation of the steam generator inspection compare software. The three‑frequency mix and additional noise/history reviews can be added to the existing frequency channels at minimal cost.

Risks

No unique risks beyond standard project risks associated with implementing changes at nuclear power plants.

SWEEP Score

Category	Level	Description
Cost	3	Implementation cost of the three frequency mix channel technique with the steam generator inspection compare software is less than $1 million. Depending on the plant’s current analysis software, the costs associated with outage inspection data preparation and quantification may already be included. If not, then data preparation and quantification costs are approximately $100,000 per unit per outage. Purchase of the compare software from the vendor costs approximately $50,000.
Savings	1	Savings are less than $1 million per year. Savings are estimated to be between $200,000-500,000 per outage based on previous implementations. Savings are driven by the size of the steam generator and the tubing material.
Payback	2	Payback period is greater than one year but less than five years (inclusive). Payback is driven by when the techniques are implemented relative to the next scheduled outage.
Technical Readiness	3	The methodology is already in use at nuclear power plants and is ready for wide operational deployment.
Licensing Readiness	3	This methodology has already been implemented at nuclear power plants.
Implementation Proficiency	3	The implementation of the enhanced bobbin eddy current coil inspection methodologies does not require knowledge in implementing digital technologies.