ML19347E030
| ML19347E030 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 03/30/1981 |
| From: | Withers B PORTLAND GENERAL ELECTRIC CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| IEB-81-01, IEB-81-1, NUDOCS 8104140711 | |
| Download: ML19347E030 (9) | |
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Mr. R. H. Engelken, Direc U. S. Nuclear Regulatory Commission, Region V 1990 N. California Blvd.
Walnut Creek Plaza, Suite 202 Walnut Creek, CA 94596
Dear Mr. Engelken:
IE Bulletin 81-01 identified problems with certain mechanical snubbers and requested that an extensive surveillance program be performed for all mechanical snubbers on safety-related systems. Ris program would require visual cxamination and manual testing of all the mechanical snubbers prior to completion of the next refueling outage. PGE requests relief from the requirements of IE Bulletin 81-01 for the reasons dis-cussed below:
1.
The Bulletin identified numerous problems with mechanical snubbers manufactured by International Nuc1 car Safeguards Corp. (INC). These failures involved snubbers being frozen due to improper assembly, overheating of internal components by welding, sensitivity of the design to dirt or corrosion, and inadequate or excessive lubrication.
Some of these snubbers were found to be frozen prior to being placed into service. There are no INC snubbers in use at Trojan. Since the problems with INC snubbers are not generic to all mechanical snubbers, they are not applicable to the Trojan Nuclear Plant.
2.
Three failure cases were cited for Pacific Scientific Corporation (PSC) mechcnical snubbers. Although these snubbers are being used at Trojan, none of these cases involved the Trojan Nuclear Plant. Two of the cases involved excessive loadings of the snubbers, while the third resulted from improper installation. The cases of excessive loadings can be attributed to a design review deficiency. The snubbers installed at Trojan were reviewed as part cf the original design review to verify proper loading, and subsequent inspections have not indicated any errors in this area. h e third case appears to be a random failure and there is no evidence 121 SW Symon St cet. Portland. Oregan 9720:
Pcrtland General E!ectricCcnpuif Mr. R. H. Engelken March 30, 1981 l
Page two to indicate that this has occurred again.
No cases of PSC snubbers being frozen due to internal corrosion or improper lubrication were cited.
In fact, the Bulletin acknowledges the high reliabil-ity of PSC snubbers by reducing the extent of the inspection program and by providing a more relaxed time frame for PSC anubber inspection as compared to that proposed for INC snubbers. However, we do not believe that the failure cases cited for PSC snubbars provides enough doubt about their present condition as to justify examination and testing of all the snubbers prior to completion of the next refueling outage.
3.
Tests have been performed recently at Trojan on more than 100 mechanical snubbers on safety-related systems.
All of these snubbers vere able to perform their intended function. A description of the tests follows:
a.
Special Plant Test 42 (Heatup Surveillance of New Mechanical Pipe Snubbers - December, 1978) involved 83 snubbers on several safety-related systems, including main steam and RCS. All were found to be operable and were able to perform their intended function.
b.
Special Plant Test 45 (Heatup Surveillance of New Mechanical Pipe Snubbers - June, 1979) involved nine snubbers on the pressurizer.
Again, all were fcund to be operable.
l c.
Response to IE Bulletin 79-13 (Inspection of l
Feedwater System Piping, May 1980) involved testing of 12 snubbers on the feedwater lines.
Test results met the criteria required in Item la of IE Bulletin 81-01 for visual exami-nation and manual tests.
Since all of these snubbers were found to be operable and since degradation over time due to corrosion is not expected to be a problem with the PSC cnubbers, an expedited additional inspection is not warranted.
4.
In response to reliability problems with hydraulic snubbers, PGE undertook an extensive modification pro-gram to replace almost all of the hydraulic snubbers with highly reliable PSC mechanica1 snubbers. As a result there are more than 350 PSC ncchanical snubbers l
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Portland General E!ectricCDipsyr Mr. R. H. Engelken March 30, 1981 Page three installed on safety-related systems at Trojan, which is more than the number of PSC mechanical snubbers installed at most of the operating nuclear plants. Manual testing of these snubbers by the end of the refueling outage scheduled for this spring could have a major impact on the outage.
It is esti=ated that an inspection program in accordance with Bulletin 81-01 would require at least a 140-man-day effort. Discussions with other utilities indicate that this estimate could be low by a significant amount. More importantly, many of these snubbers are in high radiation areas and approximately 35 percent will require scaffolding to be built in order to provide access for the inspection crews. This will result in an estimated 30 man-res radia-tion exposure, which is more than 10 percent of the total man-rem exposures received for the entire year of 1979 at Trojan. This co=es at a time when we are striving to main-tain radiation exposures as low as reasonably achievable (ALARA). A 100 percent inspection program is not justifi-able from an ALARA standpoint based on the limited number of failures and failure modes identified for PSC snubbers.
5.
Visual examination of snubbers will continue to be per-formed in accordance with the Trojan Inservice Inspection (ISI) Program. These examinations will detect cases of gross snubber misalignment or defor=ation due to excessive loadings and are performed on a routine basis under the category of Component Supports in the ISI Program. In addition, the Plant Technical Specifications are currently under review for incorporation of mechanical snubber sur-veillance requirements.
6.
A visual inspection to verify proper installation was per-formed on all of the snubbers on safety-related systems during the last half of 1979 and during 1980.
This inspec-tion was performed during the walkdown of safety-related piping that was made in response to IE Bulletin 79-14.
One snubber on the 3-inch pressurizer relief piping was found to have two of the four base plate anchor bolts nonfunctional.
An analysis =ade of the remaining two bolts indicated that the support would not have failed and that operability of the system would not have been affected. All of the remain-ing mechanical snubbers were found to be properly installed and none of the snubbers showed any evidence of damage due to excessive loadings.
Furthermore, design calculations were reviewed for exces-sive loadings as part of the response to IE Bulletin 79-14.
Since i= proper installation and excessive loadings were the only failure modes identified for PSC snubbers in
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i Pbrtland General EectricCcuwser Mr. R. H. Engleken March 30, 1981 Page four Bulletin 81-01, additional visual inspections or design reviews should not be necessary for Trojan.
In order to maintain a high confidence level that the mechanical snubbers will be operational as required, PGE proposes to perform an inspection of a carefully selected sample of the mechanical snubbers at Trojan. This program is discussed in the following responses to the action items con-tained in IE Bulletin 81-01.
Item 1 Within 30 days of the issuance date of this bulletin, all normally accessible
- INC mechanical snubbers installed on safety-related systems or in storage shall be visually examined and tested as follows:
a.
Perform a visual examination for damage and, without causing the system to be inoperable except as permitted by the facility technical specifications, verify that the snubbers 'aave
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freedom of movement by perforcing a manual test over the range of the stroke in both com-pression and tension.
b.
Perform an operability test to confirm that (1) activation (restraining action) occurs in both compression and tension and (2) the i
drag forces are within the specified range in both compression and tension. The tests shall be performed on all snubbers in stor-age and on a representative sample (10% of
'the total of this type of snubber ir ise in the plant or 35, whichever is less) of the normally accessible snubbers that are in service and can be individually removed without causing the system to be inoperable, except as permitted by the facility techni-cal specifications. For each snubber that does not meet the test acceptance criteria, an additional representative sample (as defined above) of this type of snubber shall be tested. For each of these additional i
j snubbers that do not meet the test accept-ance criteria, another representative sample
- "Normally aci essible" refers to those areas of the plant that can be entered during reactor operation.
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Pcrtfarid Gerleral Eechie Ociv aaur ry Mr. R. H. Engleken i
I March 30, 1981 Page five t
of this type of snubber shall be tested. This cycle shall be repeated until no more failures have been found or until all snubbers of this type have been tested. The samples should be made up of snubbers representing the various sizes.
c.
Snubbers which have been examined and tested in a manner comparable to Items la and ib above within the last six months may be exempted.
d.
If any failures are identified in Items la or 7
lb above, take corrective action and evaluate the effect of the failure on the system opera-bility pursuant to the facility technical i
specifications for continued cperation.
e.
If failures are identified in Items la and lb above, and if INC snubbers are known to be located in any inaccessible areas, a plant shutdown shall be performed within 30 days after the discovery of the first inoperable
,1 snubber and inspectionr, conducted in accor-j dance with Item 2a and 2b below, unless justification for concinued operation has been provided to the NRC.
Response
There are no INC mechanical snubbers installed or in l
storage at Trojan.
Item 2 Visually examine and test all inaccessible INC mechani-cal snubbers installed on safety related systems at the next outage of greater than five days duration as fol-lows:
a.
Visually examine and manually test all inac-cessible snubbers as described in Item la
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above.
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b.
Perform an operability test on a representa-l tive sample of inaccessible snubbers as described in Item lb above.
c.
Snubbers which have been examined and tested in a manner comparable to Items 2a and 2b i
I Pcrtiswxi Ger1eral Eectric Cui.yarif Mr. R. H. Engleken March 30, 1981 Page six i
above within the last six months may be exempted.
i d.
If any failures are identified in Items 2a or 2b above, take corrective action to evaluate the effect of the failure on sys-tem operability pursuant to the facility technical specifications for resuming operation.
Response
There are no INC mechanical snubbers installed at Trojan.
Item 3 Provide a schedule for an inspection program covering i
mechanical snubbers produced by other manufacturers. As a minimum, this inspection program shall:
a.
Include all snubbers installed on safety-related systems; b.
Include the visual examination and manual test described in Item la above for all snubbers; c.
Snubbers which have been examined and tested in a manner comparable to Item 3b above within the last twelve months may be exempted; j
d.
Require the corrective action and evalua-tions described in Items ld and 2d above; and Be completed prior to the completion of e.
the next refueling outage. Plants which are currently in a refueling outage should perform the visual examination and manual tests of inaccessible mechanical snubbers before resumption of operations unless some other basis for assurance of snub-ber operability is provided to the NRC.
Response
j In lieu of the above, and for the reasons discussed previously, PCE is planning to perform the following inspection program:
Portland General E!echicCcu.piuv Mr. R. H. Engleken March 30, 1981 Page seven a.
A visual examination of all the mechani-cal snubbers installed on safety-related systems will be performed to check for evi-dence of excessive loading or vibration.
b.
A representative sample of the mechanical snubbers will be manually stroke tested per Item 1.a. of the Bulletin in order to verify that they have freedom of movement over the range of the stroke in both com-pression and tension. This representative sample will include 20 percent of the total number of mechanical ~ snubbers installed on safety-related systems. The sample popula-tion will be carefully selected to include representatives from the following cate-gories:
i) Snubbers that are subject to cyclic stresses.
- 11) Snubbers on systems that are subject to high vibration ampli-tudes or impact loads such as waterhammer. (Note: waterhammer has not been known to be a prob-lem at Trojan.)
lii) Snubbers that are exposed to the environment (such as those in the facade area).
i l
Snubbers that are in high radiation exposure zones or are in locations where accessibility is limited due to physical constraints (such as the need for scaffolding) will be excluded from the representative sample for the reasons l
discussed previously. As a result of the pro-posed sampling plan, Trojan will be sampling about the same number of PSC snubbers as other operating nuclear plants.
c.
Snubbers which have been examined and tested in a manner comparable to Item 3.b. within the last 12 months may be included in the representative sample.
d.
If any mechanical snubbers are found to be inoperable due to vibration or impact loads,
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Portland General E!echicCcir.vay Mr. R. H. Engleken March 30, 1981 Page eight all of the other mechanical snubbers on the same line will be manually stroke tested. An additional 10 percent of the mechanical snub-bers will be manually stroke tested for each mechanical snubber found to be inoperable due to causes other than vibration or impact loads.
e.
This inspection program is scheduled to be com-pleted by the end of the next refueling outage.
Item 4 Submit a report of the results of the inspections, test-ing and evaluation requested in Item 1 to NRC within 45 days of the issuance date of this bulletin. Report the results of the inspections, testing and evaluation requested in Ites 2 within 30 days af ter the inspection and testing have been completed. The response to Item 3 shall be submitted within 60 days of the issuance date of this Bulletin. The results of the inspections per-formed for Item 3 shall be submitted within 60 days after the completion of the inspection.
The reports shall contrin the following:
a.
A description of the visual examinations and tests performed.
b.
Number of snubbers examined and tested. Group-ing by manufacturer name, model number, and size is acceptable, c.
Number of failures identified; manufacturer name, model number, size, mode of failure, cause of failure, corrective acti7n, snubber location, effect of failure on plant and system safety, and justification for con-tinuing or resuming operation, d.
The above information shall also be provided for the snubbers exempted by Items Ic, 2c and 3c above.
Response
PCE will submit the requested information within 60 days after the completion of the inspection.
Portland General E!ectricCoivinsy Mr. R.11. Engleken March 30, 1981 Pas;e nine The proposed inspection program will result in a confidence level greater than 95 percent that 90 to 100 percent of the mechanical snubbers will be operable when required.
In addition, the resulting radiation exposures will be kept as low as reasonably achievable.
Since the next refueling outage is scheduled to begin on May 1, 1981, your prompt concurrence with this program is requested.
Approximately 135 man-hours were expended in the review and preparation of this response.
Sincerely, a 2 Bart D. Withers Vice President Nuclear Subscribed and sworn to before me this j [*2 day of t-re, 1981.
0,u J. A f. ) L,
Notary Public of Oregon My Commission Expires:
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Mr. Lynn Frank, Director State of Oregon Department of Energy
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Director NRC Office of Inspection and Enforcement k'ashington, DC 20555 l
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