ML19339A429
| ML19339A429 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 07/22/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19339A427 | List: |
| References | |
| NUDOCS 8011030787 | |
| Download: ML19339A429 (3) | |
Text
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M /*M8 h WA?HINGTrW, D C.2C".5 ij SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING A'END:ENT NO.
TO FACILITY OPERATING LICENSE NO. DPR-3 YANKEE ATOMIC ELECTRIC COMPANY
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YANKEE NUCLEAR POWER STATION (YANKEE-ROWE)
DOCKET NO. 50-29 Introduction By application dated August 18, 1975 and supplement dated January 29, 1976, Yankee Atomic Electric Company (the licensee) requested an amendment to License No. DPR-3 for the Yankee-Rowe reactor.
The amendment would add operability (limiting conditions for operation) and surveillance require-ments for shock suppressors. (snt' hers) to the Technical Specifications.
The application is in response to our letters dated June 30, and
' De cerbe r 18, 1975, requesting a proposal in accordance with model technical specifications which we transmitted to the licensee for guidance.
Evaluation
. Snubbers are designed to prevent unrestrained pipe motion under dynamic loads as might occur during severe transients while allowing normal thermal movement during startup and shutdown.
The consequence of an inoperable snubber is an increase in the probability of structural damne to piping in the event of a severe transient which initiates dynamic roads.
It is, therefore, necessary that snubbers installed to protect safety system piping be operable during reactor g
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 failuces observed in the summer of 1973 was caused by severe degradation of seal 'naterials and subsequent leakage of the hydraulic fluid.
The basic seai materials A led in Bergen Paterson snubbers were two types of polyurethane; a miaabic gun polyester type containing plasticiters and an unadulterated molded type.
Material tests performed at several laboratories (Reference 1) established that the millable gum polyurethane deteriorated rapidly under the temperature and maisture conditions present in many snubber locations.
Although i,
the molded polyurethane exhibited greater, resistance to these conditions, bI) Report H. R. Ericksen, I;ergen Paterson to K. R. Goller, NRC, October 7,1974,
Subject:
Hydraulic Shock S::ay. Arrestors
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it also may be unsuitabic for application in the higher temperaturc
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cnvironments.
Data are not currently available to precisely define an upper temperature limit for the molded polyurethane.
The investigation indicated that seal matcrials are available, primarily ethylene propylene compounds, which should give satisfactory performance under the most severe conditions expected in reactor installations.
An extensive seal replacement program has been carried out at many reactor facilitics.
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 of snt6ber failures, some failures continue to crcur. Tnese failures have gor.erally beer, attributed to faulty snubber asserbly and insta11atica, loose fittings and connections and excessive pipe vibrations.
The failures have been observed in both PNRs and BWRs and have not been limited to units manufactured by Bergen Paterson.
Because of the continued incidence of snubber failures, we have concluded' that snubber operability and surveillance requirements should be incorporated into the Technical Specifications.
We have further concluded that these 2cquirements should be applied to all safety related snubbers, regardless of manufacturer, in all light water cooled reactor facilitics, h'c have developed the attached Technical Specificaticas to provide additional assurance of satisfactory snubbers performance and reliability.
The specifications require that snubbers be operabic 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.
The licensee will be expected to commence 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 major component would not necessarily result from the failure of a single snubber to operate as desinned, and even a snubber devoid of hydraulic fluid would provide support for the pipe or component and reduce pipe notion. The likelihood of a severe transient ocicurring 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 prodde a'dditional assurance that the sntbbers remain operabic.
The inspection frequency is based upon maintaining a constant 1cyc1 of snubber protection.
Thus the required inspection intervals varies inversely with the observed snubber failures.
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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 tha't the required surveillance program should provide an acceptabic Icvel of snubber per-formance provided that the seal materials are compatibic 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 established or an appropriate seal change is co=pleted.
To further increase the level of snubber reliability, the Technical Specifications require functional tests of snubbers at 1 cast once each re fueling ' cycle.
The tests will verify proper pisten movement, lock up and biced.
h'e have concluded that the proposed additions to the Technical Specifications, as modified, increase the probability of successful snubber perfomance, incrcase reactor safety and we therefore find them acceptable.
Environmental Consideration 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.
Ilaving made this
. determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmenta-1 impact and pursuant to 10 CFRJ 31.5(d)(4) that an environmental statement, negative declaration, or environmental appraisal need not be prepared in connection with the issuance of this amendment.
Conclusion h'c 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 pub'lic 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 atendment will _not be inimical to the cor=on defense and security or to the health and safety of the public.
Date: July 22, 1976 u r 4 %; btiggg N!
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