ML25206A065
| ML25206A065 | |
| Person / Time | |
|---|---|
| Issue date: | 07/25/2025 |
| From: | Yuken Wong NRC/NRR/DEX/EMIB |
| To: | |
| References | |
| Download: ML25206A065 (1) | |
Text
NRC Staff Presentation 2025 ASME/NRC OM Symposium Yuken Wong Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 1
Disclaimer This presentation was prepared by staff of the U.S. Nuclear Regulatory Commission (NRC). It may present information that does not currently represent an agreed upon NRC staff position. NRC has neither approved nor disapproved the technical content.
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Topics
- 1. Adjustments for Instrument Inaccuracies for Pump Tests
- 2. Pump Casing/Support Degradation 3
- 1. Adjustments for Instrument Inaccuracies for Pump Tests 4
Do pump test acceptance criteria need to account for instrument inaccuracies?
- American Society of Mechanical Engineers (ASME) Operation and Maintenance (OM) Code has specific requirements for the pump periodic verification test
- NUREG-1482, Guidelines for Inservice Testing at Nuclear Power Plants, contains guidance on adjustments for instrument inaccuracies 5
OM Code, 2022 Edition 6
- 1) Instrument accuracy shall be selected by the Owner such that the required parameters are verified when instrument accuracy is taken into account for the pump periodic verification test flow and pressure.
OM-2012 thru 2017 7
Appendix V, Pump Periodic Verification Test Program
- Paragraph V-3000(f):
account for the pump periodic verification test instrument accuracies in the test acceptance criteria
NUREG-1482, Rev. 3 8
Section 5.8, Adjustments for Instrument Inaccuracies If the accuracy of plant instrumentation used for IST activities for pumps is not well understood, the test results may not be adequate to meet the licensees safety analysis, even if they meet the OM Code requirements. For example, TS or the FSAR might require a pump to produce 1,000 gpm at 500 pounds per square inch differential (psid), but the IST reference values are 1,000 gpm (fixed) and 550 psid. The low end of the acceptable range for differential pressure from Table ISTB-5121-1 for Group A and Group B tests (0.90) would be 495 psid, although conservatively set at 500 psid. If this test is also to prove operability of the pump in addition to meeting IST requirements, and the +/-2 percent instrument inaccuracies were taken into account for flow rate and differential pressure, there is the possibility that the pump is putting out less than the required values. In this example, the instrument accuracies would need to be taken into account if they were not already considered when the design parameters were developed.
What About Inservice Tests for Trending Data?
9 NUREG-1482, Section 5.8:
For example, when obtaining values using instrumentation that meets the accuracy requirements specified for IST activities, the value as-read would be used.
Only when instruments are used that cannot meet the specified accuracy for a test would an adjustment be necessary to meet the OM Code.
Other Inservice Tests for Trending 10 NUREG-1482, Section 5.5.1, Range and Accuracy of Analog Instruments If relief is requested, the licensee would typically describe the effect on each group of applicable pumps and would typically discuss adjustment of acceptance limits to account for the inaccuracies.
No indication of instrument accuracy not met in this paragraph.
If the instruments do not meet the intent of the OM Code requirements, the NRC may require the licensee to adjust acceptance limits to account for the instrument inaccuracies.
Adjust acceptance limits only if instrument accuracy not met
NUREG-1482 Guidance Summary 11
- Account for instrument inaccuracies in the test acceptance criteria if the test is to verify design basis flow and pressure Applies to pump periodic verification test Also applies to comprehensive test and Group A test if they are credited for this purpose
- No need to account instrument inaccuracies for inservice tests for trending purposes (if instruments meet the OM Code accuracy requirements)
- 2. Pump Casing/Support Degradation 12
Pump Structural/Pressure Boundary Degradation The NRC is sharing operating experience regarding external degradation of components
- Pump casing or support degradation was not identifiable via IST
- 10 CFR 54.21 requires passive components (pump casing and supports) be within the scope of license renewal and subject to aging management review
- However, plants aging management program did not identify the extent of degradation The extent of degradation called into question the operability of the components 13
Pump Structural/Pressure Boundary Degradation (cont.)
- Severe degradation was identified by NRC inspection team
- Multiple findings for failure to identify corrosion and conduct operability determinations.
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- Structural support bracket 15
Overhaul Procedure Steps Not Performed to Manage Aging Effects
- Pump removal and replacement procedure was credited to manage corrosion and aging effects.
- Procedure directed maintenance staff to visually examine the pumps volute, front head, handhold covers, and pump bolting for corrosion and pitting. Maintenance staff did not identify severe corrosion.
- Procedure directed removal of excessive accumulation of biofouling agents, corrosion products, and silt from volute, front head, handhold covers, and bolting. Maintenance staff did not remove excessive corrosion products to examine the base metal.
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Resolution
- The NRC team observed severe corrosion that called into question operability.
- Subsequently, licensee cleaned the components, performed examinations, evaluated the as-found conditions, and performed operability evaluations.
- Licensee entered deficiencies in the corrective action program.
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QUESTIONS?
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- ASME: American Society of Mechanical Engineers
- CFR: Code of Federal Regulation
- FSAR: Final Safety Analysis Report
- IST: Inservice Testing
- NRC: U.S. Nuclear Regulatory Commission
- NUREG: U.S. Nuclear Regulatory Commission technical report designation
- OM: Operation and Maintenance
- TS: Technical Specifications 19