ML20049J242
| ML20049J242 | |
| Person / Time | |
|---|---|
| Issue date: | 03/11/1982 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Eisenhut D, Jordan E, Mausshardt D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE), NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS), Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20049J243 | List: |
| References | |
| NUDOCS 8203120300 | |
| Download: ML20049J242 (4) | |
Text
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MAR 111982 o
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fEMORAtlDUM FOR: Darrel G. Eisenhut, NRR y,,,c[/hh 3
Edward L. Jordan, IE
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Donald B. Mausshardt, NMSS M
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Robert M. Bernero, RES M
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Clemens J. Heltemes, Jr., AEOD
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FROM:
Victor Stello, Jr.
~ iR Deputy Executive Director Regional Operations and Generi:: Requirements
SUBJECT:
AGEllDA ITEM (BRIEFIflG) FOR CRGR - IE CIRCULAR 82 -
SURVEILLAtlCE OF HYDRAULIC StiUBBERS The following material listed below is enclosed for your information regarding the proposed IE circular on Surveillance of Hydraulic Snubbers:
- 1) Brief summary of the circular and associated issues that CRGR should address.
- 2) Proposed IE Circular with transmittal memorandum (E.L. Jordan to V. Stello, Jr.) of February 12, 1982.
Original signed by
.vurley Victor Stello, Jr.
- Deputy Executive Director
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Regional Operations and Generic Requirements 1
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l BRIEFING ITEM:
IE CIRCULAR - SURVEILLANCE OF HYDRAULIC SNUBBERS IDENTIFICATION: Briefing on proposed IE Circular on Surveillance of Hydraulic Snubbers.
It summarizes recent operating experience with snubbers and recommends licensee and construction permit holder actions that emphasize early detection and correction of hydraulic snubber failures and vibration and shock loading conditions that caused the failures.
DESCRIPTI0il:
Portions apply to licensees of operating nuclear power piarts or holders of construction permits fcr nuclear power plants.
OBJECTIVES: o Promulgate recent operating experience with hydraulic snubber failures.
o Recommend for operating plants that sample selection of snubbers, whose surveillance testing is now required by Technical Specifications be biased toward systems subject to vibration and shock loadings; that snubbers showing wear be repaired or replaced; and that design review or more preventive maintenance be done for systems with snubber failures due to vibration and shock loadings.
o For CP holders, that proper design review, snubber selection and preventive maintenance be performed during construction to resolve these potential problems.
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P BACKGROUND: o Several LERs from Carolina Power and Light Company and Sacramento Municipal Utility-District document failures of significant numbers of snubbers for a variety of reasons.
o IE Information Notice 79-01 on snubber failures.
o Correspondence from a snubber vendor on technical improvements to reduce failure.
BASIS:
Information on operating experience in the Circular deserves widespread promulgation to licensees and CP holders. The high failure rate of snubbers subjected to vibration and shock loading warrants NRC recommendations that would cause greater attention by, licensees to early detection of failed snubbers in susper t subpopulations.
CONTACTS: Spokesman:
R.J. Kiessel (24796)
Sponsor:
E.L. Jordan, IE CRGR:
E.B. Blackwood (24359)
KEY ISSUES:
1.
What is the impact on the statistical validity and level of significance that could be attributed to the entire population of snubbers based on an intentionally biased sample?
If a biased sample is used and existing (new or old) Technical Specification sampling requirements are not statistically valid, would the biased sample represent an improvement in safety over existing sampling plans?
2.
To what extent (or percent) should the sample be biased toward the subpopulation of snubbers subjected
I to kncwn vibration and shock loadings? The Circular doesn't quantify the bias.
Concentration on this subpopulation may be accompanied by the risk presuming that it contains the dominant cause of snubber failure. Unknown causes of failure might escape detection due to the bias.
- 3. Should the sequential sampling plan in Technical Specifications remain the same even though the sample is biased toward snubbers having a higher probability of failure than the overall population? If so, more failures would be detected causing more snubbers to be tested.
Is any increase in confidence that might result from biasing the sample and testing more snubbers worth the additional impact on licensees during refueling outages?
The Circular does not estimate this impact.
- 4. If a subpopulation of snubbers exposed to vibration and shock loading does exhibit si gnificantly higher failure rates, should this subpopulation be separated from other snubbers and have its own sampling plan?
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