ML20049J248
| ML20049J248 | |
| Person / Time | |
|---|---|
| Issue date: | 02/12/1982 |
| From: | Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| Shared Package | |
| ML20049J243 | List: |
| References | |
| REF-SSINS-6830, REF-SSINS-9156, REF-SSINS-SSINS-6, REF-SSINS-SSINS-9 NUDOCS 8203120309 | |
| Download: ML20049J248 (4) | |
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UNITED STATES ~
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WASHINGTON, D. C. 20555 SSINS 6830 FEB 121982 9156 MEMORANDUM FOR: Victor Stello, Jr., Deputy Director for Regional Operations and Generic Requirements FROM:
Edward L. Jordan, Director, Division of Engineering and Quality Assurance IE
SUBJECT:
IE CIRCULAR ENTITLED SURVEILLANCE OF HYDRAULIC SNUBBERS The subject IE circular is forwarded for consideration by the Committee for the Review of Generic Requirements.
For the operating plants, the circular's recommended actions involve a redirection rather than an increase in the inspection and testing activities currently required by the technical specifications. This redirection does increase the probability of early detection of failures in systems which experience vibration or shock loadings.
If such failures do exist, once they are detected, this circular may result in in-creased testing and mainteaance during the affected refueling outage. However, it is estimated that there will be no increase in either the staff's or the utilities' activities over a number of refueling outages.
Additionally, it is estimated that there will be no increase in the collective occupational dose over a similar period of time.
For the plants under conpruction, the circular's recommended actions involve an increase in the current cL. sign activities of the utilities, particularily in the areas of hydraulic snubber selection and redesign of systems which experience vibration and shock loadings. Although attempts to formally quantify this in-creased activity have not been made, it is estimated that they will be nominal.
However, it is estimated that this increase in the staff's and utilities' activities will be more than offset by the reduced hydnulic snubber replacement and modifica-tion activities over the life of the plant which will result from these design activities. Additionally, it is estimated that there will be a decrease in the collective occupational dose over the life of the plant because of the reduced re-placement and modification activities.
As a result, it is recommended that the subject circular be approved for issuance without a formal impact statement.
If you deem that a presentation before the full committee is necessary or desirable, please inform me of the scheduled date for such a presentation.
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Edward ordan, Director Divisi of Engineering and Quality Astu' nce, IE CONTACT:
R. J. Kiessel 49-24796 8203120309 820311 PDR REVGP NRCCRGR PDR
Victor Stello, Jr.
Enclosure:
IE Circular 82-
D. G. Eisenhut, NRR R. L. Baer, IE A. W. Dromerick, IE l
W. S. Schwink, ED0 l
R. J. Kiessel, IE b
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MEMORANDUM FOR:
Ronald C. Haynes, Regional Administrator, Region I James P. O'Reilly, Regional Administrator, Region II James G. Keppler, Regional Administrator, Region III John T. Collins, Regional Administrator, Region IV Robert H. Engelken, Regional Administrator, Region V FROM:
Edward L. Jordan, Director, Division of Engineering and Quality Assurance, Office of Inspection and Enforcement
SUBJECT:
IE CIRCULAR 82-SURVEILLANCE OF HYDRAULIC SNUBBERS The subject circular is enclosed for issuance on February
, 1982.
The circular should be issued recommending action to all nuclear power reactor facilities holding an operating license or a construction permit.
A draft copy of the transmittal letter is also enclosed.
Edward L. Jordan, Director Division of Engineering and Quality Assurance Office of Inspection and Enforcement
Enclosure:
1.
Draft transmittal letter
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2.
IE Circular No. 82-l cc:
R. C. DeYoung, IE H. L. Whitener, R1l CONTACT:
R. J. Kiessel, IE 49-24796
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(Draft transmittal letter to all power reactor facilities holding an operating I
license or construction permit.)
(
IE Circular No. 82-SURVEILLANCE OF HYDRAULIC SNUBBERS Addressee:
The enclosed circular is forwarded for your appropriate action.
No written response to this circular is required.
If you have any questions i
P related to this matter, please contact this office.
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Sincerely, Signature (Regional Administrator)
Enclosure:
IE Circular No. 82-l S
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.r SSINS No.:
6830 Accession No.:
8107230045 IEC 82-UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 February
, 1982 IE CIRCULAR No. 82-SURVEILLANCE OF HYDRAULIC SNUBBERS
===.
Background===
On March 18, 1981, Carolina Power and Light Company (CP&L) reported (LER 81-041/03L) that 21 out of 101 Bergen-Patterson hydraulic snubbers were considered inoperable after functional testing at the Brunswick 2 facility.
This represented a failure rate of approximately 20 percent.
Failures were identified in systems such as residual heat removal, reactor building closed cooling water, fuel pool cooling, core spray, reactor core isolation cooling, and high pressure coolant injection.
Of the snubbers that failed to meet the acceptance criteria, about 30 percent were declared inoperable because they failed to lock up within the required velocity.
As a result of.
the high percentage of failures and the modes of failure, the licensee shut the reactor down on March 4,1981 and implemented an extended snubber test program.
CP&L's supplements to the LER, submitted on June 1,1981 and January 7,1982 reported that 130 out of a total of 640 snubbers had failed the functional test.
This represented a failure rate slightly in excess of 20 percent.
In addition to rebuilding all failed snubbers, another 80 which had marginally met the acceptance criteria were rebuilt for purposes of preventive maintenance.
CP&L's evaluation of the test and examination results indicated that a major cause of failure to pass the func;ional test was low bleed rate (45 percent of those rebuilt).
Table I lists the reasons snubbers failed the functional tests.
Those snubbers that were rebuilt were examined and the types of degradation observed were noted.
Table II lists the types of degradation that were observed.
The most common types of degradation were worn poppets (62 percent), spring capture (36 percent), piston / cylinder wear (31 percent), and deteriorated seals (28 percent).
Some of the snubbers exhibited more than one form of degradation accounting for a percentage total greater than 100 percent.
An attempt was made to relate the observed degradation to the reason the snubber failed the functional test.
Table III lists all of the identified rejection modes.
The most common rejection modes were worn poppets (27 percent) and spring capture (16 percent).
That is, although worn poppets were observed in 62 percent of de snubbers examined, only 27 percent of the test failures could be positively attributed +.o that cause.
The three major types of deg.'adation (worn poppets, spring capture, and piston /
cylinder wear) appear to be cov equences of service-related conditions.
Pipe vibrations cycle the snubbers to the extent that the grooves on the poppet heads begin to wear, and the pistons wear on the cylinder walls.
Continued cycling
IEC 82-February
, 1982 Page 2 of 4 causes the retaining springs to fail or deform in such a way that the springs can be captured.
Of the snubbers rebuilt, 37 percent were determined to be service sensitive.
That is, the operating conditions of the line or snubber were found to have signs of vibration or water hammer'and these conditions could f
cause the type of degradation found.
Most of the service-sensitive snubber failures were attributed to vibration; a nominal number were caused by water hammer.
i CP&L is replacing the poppet valve bodies with a new, more vibration resistant one developed by Bergen-Patterson.
However, until lengthy service demonstrates I
the effectiveness of this modification, it would be prudent to maintain high levels of surveillance and preventive maintenance on hydraulic snubbers subject to vibration or shock loadings that can reduce their ser.-ice life.
Additionally, i
consideration should be given to system design alternativ's which reduce, to the maximum extent possible, or preclude such vibrations tr shock loadings.
A similar problem at Rancho Seco was discussed in IE Infornation Notice 79-01 based on information reported on December 4, 1978, (LER 78-015/01T) and January 12 and 15, 1979, (LER 78-017/03L) by Sacramento Municipal Utility District.
Subsequent correspondence from Bergen-Patterson indicated that their intended modifications to these snubbers would include case hardening of the entire valve body, extending the cavity in which the end of the spring coil is guided, and reducing the axial travel of the poppet by increasing the length of the poppet stop.
The number of failures experienced tend to compromise capability of the affected systems to function properly during operational transients and to withstana seismic events.
Recommended Actions to be Taken by Licensees of Operating Plants:
1.
During the next refueling outage, the sample of hydraulic snubbers to be functionally tested in accordance with the technical specifications should be biased toward hydraulic snubbers installed on:
Systems that have experienced or are subject to sudden piping movement a.
from operational transients which results in lockup of the hydraulic snubbers.
b.
Systems that have experienced or are subject to either intermittent or continuous vibrations of a type which results in repeated lockup and release of the hydraulic snubbers.
2.
If defective snubbers are found on the above systems:
For plants which have not begun using the revised snubber technical a.
specifications
- the additional samples required by the technical specifications should also be biased as described in item 1 above.
- The. revised technical specifications are those submitted and approved in response to Revision 1 of the Inservice Surveillance Requirements for snubbers as transmitted by Darrell G. Eisenhut on November 20, 1980.
.I IEC 82-February
, 1982
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Page 3 of 4 b.
For plants which have begun using the revised taubber technical specifications *, the identified defects should be reviewed to determine if a design defect exists.
Where a design defect is identified, the additional functional testing and engineering evaluations required by the technical specifications should be performed.
s (It should be noted that the above are consistent with the industry
[
recommendations found in Section ER-3350-1 of Draft 6 to ANSI /ASME O&M-4,
" Examination and Performance Testing of Nuclear Power Plant Dynamic l
Restraints (Snubbers)", which states, "For the purpose of establishing i
sample composition for additional tests, the sample should be based on a failure analysis of the unacceptable snubber or' snubbers.
Additional snubbers selected for testing shall be those which may be expected to have the same or similar. deficiencies as the unacceptable snubber or snubbers.")
3.
Snubbers showing signs of worn poppets, spring capture, or piston / cylinder wear should be replaced or rebuilt.
4.
Repeated instances of snubber failures due to vibration or shock loadings should be cause for a design review of the system and/or increased levels of preventative maintenance.
Current technical specifications require periodic inspection and testing of hydraulic snubbers.
The above recommended actions involve a redirection of activities to increase the probability of early detection of failure.s in systems that. e.voerience vibration or shock loadings.
Once such failures are detected, tiiis circular may. result in increased testing and maintenance during the affected refueling outage.
However, the NRC staff has estimated that there will be no increase in the collective occupational dose due to implementing the above recommended actions over a number of refueling outages.
If your plant specific estimate results in collective doses substantially in excess of this estimate after all relevant ALARA actions have been considered and applied as appropriate, you should contact the regional administrator of the appropriate NRC Regional Office to determine whether your dose estimate might justify changes in the recommended actions.
Recommendations for Holders of Construction Permits:
1.
The snubbers specified and installed should be specifically designed for the level of vibration and shock loadings inherent in the system..
2.
System designs should be reviewed to reduce to the maximum extent practical or preclude vibrations or shock loadings that could cause degradation of the snubbers on the system.
3.
Preventive maintenance programs sfiould be developed to provide for increased levels of activity on snubbers subjected to significant vibration or shock loadings.
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IEC 82-
'l February
, 1982 Page 4 of 4 i
No written response to this circular is required.
If you need additional l
information regarding this subject, contact the Regional Administrator of f
the appropriate NRC Regional Office.
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Attachment:
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Tables I, II and III i
2.
Recently issued IE Circulars 1
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r-IEC 82-February
, 1982-l TABLE I REASON SNUBBER FAILED FUNCTIONAL TEST Percent of Reason Total Rebuilt Low Bleed 45 High Lockup 17 High Bleed 13 No Lockup 13 Other 12 TABLE II DEGRADATIONS FOUND Percent of Reason
. Total Rebuilt
- Worn Poppets 62 Spring Capture 36 Piston / Cylinder Wear 31 Deteriorated Seals 28 Grease in Fluid 7
Side Loading 7
None 8
TABLE III REJECTION MODE Percent of Reason Total Rebuilt Worn Poppets 27 Spring Capture 16 Deteriorated Seals 3
Piston / Cylinder Wear 3
Side Loading 1
Grease in Fluid 1
Inconclusive Evidence 41 Miscellaneous 8
^ Note:
These percentages total more than 100 percent because some of the snubbers exhibited more than one form of degradation.
l i-IEC 82-January
, 1982 RECENTLY ISSUED IE Circulars will be included on final when IEC No. and issue date are inserted.
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