ML19210B629
| ML19210B629 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 02/17/1977 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19210B623 | List: |
| References | |
| NUDOCS 7911110104 | |
| Download: ML19210B629 (4) | |
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%,t UNITED STATES NUCLEAR REGULATORY COMMISSION
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j WASHINGTON D.C.20555
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f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENI TO LICENSE NO.
DpR-50 METROPOLITAN EDISON COMPANY JERSEY CENTRAL POWER & LIGHT COMPANY
, PENNSYLVANIA ELECTRIC COMPANY THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 1 DOCKET NO. 50-289 i
Introduction During the summer of 1973, inspections at two reactor facilities revealed I
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 Enforcement required each operating reactor licensee to imediately inspect all Bergen Paterson snubbers utilized on safety systems and to reinspect them j
45 to 90 days after the initial inspectian. Snubbers supplied by other manufacturers were to be inspected on a lower priority basis.
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Since a long term solution to eliminate re:urring failures was not g
imediately available, the Division of Operating Reactors sent a letter dated 1ctober 2, 1973, to operating facilities util.izing'Bergen Paterson snubbers specifying continuing surveillance requirements and requesting pl a submittal of proposed Technical Specifications for a snubber surveil-lance program. Model technical specifications were transmitted by
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our letter of July 8,1975~, and a revision of the model technical specifications was transmitted by our letter of December 18, 1975.
n Based on these transmittals, Metropolitan Edison Company on August 23, 1975 and September 15 and October 19, 1976, proposed Technical Speci-i fications for hydraulic snubbers at Three Mile Island Unit No.1.
During our review of the proposed changes, we found that certain modifications were necessary. These modifications were discussed with Metropolitan Edison Company and have been incorporated into the proposed Technical Specifications.
E_ VALUATION Snubbers are designed to prevent unrestrained pipe motion under dynamic loads as might occur during an earthquake or severe transient while allowing normal thermal movements during startup and shutdown.
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,.., The conrequence of an inoperable snubber is an increase in the proba-bility of structural damage to piping resulting from a seismic or other postulated event which initiates dynamic loads.
It is, there-fore, necessary that snubbers installed to protect safety system piping be operable during reactor operation and be inspected at appropriate intervals to assure their operability.
Examination of defective snubbers at reactor facilities has shown that the high incidence of failures observed in the sumer of 1973 was caused by severe degradation of seal materials and subsequent leakage of the hydraulic fluid. The basic seal materials used in Bergen Paterson snubbers were two types of polyurethane; a millable gum polyester type containing plasticizers and an unadulterated molded type. Material tests performed at several laboratories (Reference 1) established that the millable g'um polyurethane deteriorated rapidly under the temperature and moisture conditions present in many snubber locations. Although the molded polyurethane exhibited greater resistance to these conditions, it also may be unsuitable for application in the higher temperature environments. Data are not currently available to precisely define an upper temperature limit for the molded polyurethane.
1 The investigation indicated that seal materials are available, primarily ethylene propylene compounds, which should give satisfactory performance under the most severe conditions expected in reactor installations, i
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. Although the seal replacement program has significantly reduced the incidence
.I of snubber failures, some failures continue to occur. These failures
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have generally been attributed to faulty snubber assembly and installation, O
loose fittings and connections and excessive pipe vibrations. The f'
failures have been observed in both PWRs and BWRs and have not been limited to units manufactured by Bergen Paterson. Because of the l
continued incidence of snubber failures, we have concluded that snubber,
i 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 f
regardless of manufacturer, in all light water cooled reactor facilities.
The proposed Technical Specifications and Bcses provide additional assurance of satisfactory snubber performance and reliability. The specifications require that snubbers be operable during reactor operation and prior to startup. Because snubber protection is required only during low probability events, a period of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is allowed for repair or replacement of defective units before the reactor must be shut down.
1 Report H. R. Erickson, Bergen Patersen to K. R. Goller, NRC, October 7,1974,
Subject:
Hydraulic Shock Sway Arrestors F -. n 0055 4
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, The licensee will be expected to connence repair or replacement of a failed snubber expeditiously. However, the 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 other safety-related equipment and provides for remedial action to be taken in accordance with 10 CFR 50.36(c)(2). Failure of a pipe, piping system, or mdor component would not necessarily result from the failure of a single snubber to operate as designed, and even a snubber devoid of hydraulic fluid would provide support for the pipe or component and reduce pipe
. notion. The likelihood of a seismic event or other initiating event occurring during the time allowed for repair or replacement is very small. Considering the large size and difficult access of some snubber units, repair or replacement in a shorter time period is not practical.
Therefore, 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 period for remedial action to be taken.
An inspection program is specified to provide additional assurance that the snubbers remain operable. The inspection frequency is based upon maintaining a constant le rel of snubber protection. Thus the required inspection interval varies inversely with the observed snubber failures. The longest inspection interval allowed in the Technical Specifications after a record of no snubber failures has been established is nominally 18 months. Experience at operating facilities has shown that the required surveillance program should provide an acceptable level of snubber performance povided that the seal materials are L
compatible with the operating environment. Snubbers containing seal material which has not been demonstrated to be compatible with the operating environment are required to be inspected every 31 days until the compatibility is esttAlished or an appropriate seal change j
is completed, f
To further increase the level of snubber reliability, the Technical l
Specifications require functional tests. The tests will verify proper piston movement, lock up and bleed.
We have concluded that the proposed Technical Specifications, as modified, increase the probability of successful snubber performance, increase reactor safety and we therefore find them acceptable.
We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having'made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR 551.5(d)(4) that an environmental statement, or negative declaration, and environmental appraisal need not be prepared in connection with the issuance of this amendment.
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-,,, CONCLUSION We have concluded, based on the considerations discussed above, that:
(1) because the changes do not involve a significant increase in the probability or consequences of accidents previously considered and do not involve a significant decrease in a safety margin, the changes do 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 connor. defense and security or to the health and safety of the public.
Date: February 17, 1977 A
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