ML19261C364
| ML19261C364 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 02/26/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19261C360 | List: |
| References | |
| NUDOCS 7903220334 | |
| Download: ML19261C364 (5) | |
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UNITED STt TES l.,
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 37 TO FACILITY OPERATING LICENSE NO. NPF-1 PORTLAND GENERAL ELECTRIC COMPANY THE CITY OF EUGENE, OREGON PACIFIC POWER AND LIGHT COMPANY TROJAN NUCLEAR PLANT DOCKET NO. 50-344 Introduction During the summer of 1973, inspections at two reactor facilities revealed a high incidence of inoperable hydraulic shock suppressors (snubbers) manufactured by Bergen Paterson Pipesupport Corporation.
As a result of those findings, the Office of Inspection and Enforce-ment required each operating reactor licensee to imediately inspect all Bergen Paterson snubbers utilized on safety systems and to re-inspect them 45 to 90 days after the initial inspection. Snubbers supplied by other manufacturers were to be inspected on a lower priority basis.
Our review of snubber operating experience indicated a ne'ed for Technical Specifications governing their operability and surveillance. Accordingly, when the operating license for Trojan was issued in November 1975, requirements for snubber operability and inspection were included.
Since that time, the NRC staff has developed improved model Technical Specifications for hydraulic snubbers. These were transmitted to Portland General Electric Company (PGE) by letter dated August 25,1976, with a request that the model Technical Spe 1fications be adopted for the Trojan Nuclear Plant.
Discussion The current Technical Specifications for Trojan require that hydraalic sr.ubbers be inspected for operability after 4 - 6 months of initial operation and every 18 nonths thereafter by verifying proper fluid level in the reservoirs.
7 0 0322033 Y
. By letter dated August 10, 1977, the licensee advised that all safety-related hydraulic snubbers rated at less than 50,000 pounds (force)
(50 kips) would be changed to mechanical snubbers of at least equiva-lent rating. This has been completed, and therefore most of the snubbers now installed at Trojan are not the type of concern here. The licensee proposed that the current Technical Specification for hydraulic snubbers be left in place for the remaining 20 hydraulic snubbers. These are large capacity snubbers (greater than 50 kips) located on the steam generators and main steam lines inside containment. Whereas the Technical Specifications which currently apply to these remaining snubbers do bear a facial resemblance to the improved model Technical Specifications (discussed below) as applied tc large (greater than.50 kips) snubbers, they do not require ir. creased inspection as. a function of the number of. observed failures, nor do they highlight the importance of proper hydraulic seal material as the model Technical Specifications do.
In addition, the model Technical Specifications require periodic functional testing for smaller (less than 50 kips) snubbers. This would have application for Trojan should smaller hydraulic snubbers be added later.
Following discussions between the licensee and the NRC staff, the licensee proposed, in a letter dated September 1,1978, that the model Technical Specifications be adopted at Trojan.
' Evaluation Snubbers are designed to prevent unrestrained motion of piping or components under dynamic loads as might occur during an earthquake or severe transient while still allowing nornal thermal movement during startup and shutdown.
The consequence of an inoperable snubber is an increase in the probability of structural damage to piping resulting from a seismic cr other postulated event which initiates dynamic loads.. It is, therefore, necessary that snubDers installed to protect safety system piping be operable during reactor operation and be insoected at appropriata intervals to assure their operability.
Examination of defective snubbers at reactor facilities has shcws that the high incidence of failures ODserved in the summer of 1973 was causec by severe degradation of seal materials and suosecuent leaka;e cf tne hydraulic flui d.
Tne basic seal materials used in Berge-Fa:ers:n snubbers were vo ty7es of polyuretnane; a nillable gu ::lyeste~ ty:e containing plastici:ers and an unaculterated nolded type. Mete-ial tests
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3 perfomed at several laboratories (Reference 1) established that tne millable gum polyurethane deteriorated racidly under the te perature and moisture conditions present in many snubber locations. Although the molded polyurethane exhibited greater resistance to these cencitions, it also may be unsuitable for application in tne higher terperature environnents.
Data are not currently available to precisely define an upper te iperature limit for the molded polyurethane. The investigation indicated that seal materials are available, primarily ethylene propylene ccr.counds, which should give satisfactory perfomance under tne most severe conditiers expected in reactor installations.
An extensive seal replacement program has been carried out' at many reactor facilities. Experience with ethylene propylene seals has been very good with no serious degradation reported thus far. The seal material used in the four main steam line snubbers at Trojan 'is ethylene propyler., which is acceptable for this application. The seal material for the sixteen steam generator snubbers is Viton A.
This material has been environmentally tested, and is also accept-able for this service.
Operating experience thus far at Trojan bears this out - no failures leading to inoperable safety-related snubbers have been observed.
Although the seal replacement program has significantly reduced the incidence of snubber failures, some failures continue to occur. These failures have generally been attributed to faulty snubber assembly and installation, loose fittings and connections and excessive pipe vibrations. The failures have been observed in bei,h PWRs and BWRs and have not been limited to units manufactured by Bergerf Paterson.
Because of the continued incidence of snubber failures, we have con-cluded that improved snubber operability and surveillance requirements should be incorporated into the Technical Specifications. We have further concluded that these requirements should be applied to all safety related snubbers, regardless of manufacturer, in all light water cooled reactor facilities.
l Report H. R. Erickson, Bergen Paterson to K. R. Goller, NRC, October 7,1974,
Subject:
Hydraulic Shock Sway Arrestors
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We have develooed the attached Technical Specifications and Eases to provide additional assurance of satisfactory snubber perfor.ance and reliability.
The specifications require that snuboers be operable during reactor operation and prior to startup.
Because snub:er prete:: ion is recuired only during low probability events, a period of 72 h:urs is allowed for repair or reolacement of defective units before tne reactor must be shut down. The licensee will be expected to com lence re: air or replacement of a failed snubber exceditiously.
However, tne allowance of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is consistent with that provided for otqer safety-related equipment and provides for remedial a: tion to be taken in accordance with 10 CFR 50.36(c)(2).
Failure of a pice, piping system, or major conponent would not necessarily resu::
from the failure of a single snubber to operate as designed, and even a snubber devoid of hydraulic fluid wculd provide succo-:
for the pipe or comannent and reduce Dice motion.
Tne likelinoce of a seismic event cr other ir.itiating event occurring durin-the time allowed for repair or replacement is very small.
Consicering the large size and difficult access of some snubber units, reoair or replacement in a shorter tine period is not practical.
Trerefore, the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> period provides a reasonable and realistic perio: for remedial action to be taken.
An improved inspection program is specified to provide additional assurance that the snubbers remain operable.
The inspection frequen:y is. based upon maintaining a constant level of snubber protection.
Thus the required inspection interval varies inversely,with the observed snuboer failures. The longest inspection interval allowed in the Technical Specifications after a record of no snubber failures has been established is nominally 18 months.
Excerience at operating facilities has shown that the required surveillance program should provide an acceptable level of snubber perfonnance provided that the seal materials are compatible with the operating environment.
Snubbers cen-taining seal material which has not been demonstrated to be :crrcatible with the operating environment are required to be inspected every 31 days until the compatibility is established or an appropriate seal change is completed.
Snubber inspections at Trojan have been conducted as currently specified - before 6 months of initial plant operation and again at 18 months. No inoperable snubbers were found.
Based on this operating experience, we conclude that the inspection frequency should continue at once per 18 months for the present.
This schedule is consistent with the proposed model Technical Specifications. The next inspection should therefore be made 18 months from the last inspection.
We have concluded that the proposed additions to the Technical Specifications, as modified, increase the probability of successful snubber performance, increase reactor safety and we therefore find, thet acceptable.
EN":F7;" ENTAL CONSIDERATION We have determined that the ariendment does not authori.ze a change in effitent tyoes or total amounts nor an increase in power level and will net result in any significant environmental iroact.
Havin; nade this determinatien, we have further concluded that the ameni ent involves an action which is insignificant from the standocint of environmental impact and oursuant to 10 CFR 551.5(d)(4) that an environmental imoact statement, or negative declaration and environ-rental aporaisal need not be orepared in connection with the issuance of this amendment.
CON LUSION We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the prcbability or consecuences of accidents oreviously considered and does not involve a significant decrease in a safety narcin, the anenement does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date: February 26, 1979