ML19209A391
| ML19209A391 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 09/30/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19209A389 | List: |
| References | |
| NUDOCS 7910030779 | |
| Download: ML19209A391 (5) | |
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SAFETY EVALUATION REPORT STEAM GENERATOR WATER HAMMER KEWAUNEE POINT BEACH UNITS 1 AND 2 PRAIRIE ISLAND UNITS 1 AND 2 SEPTEMBER 1979 P
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1.0 INTRODUCTION
Steam generator water hammer has occurred in certain nuclear power plants as a result of the rapid condensation of steam in a steam generator feedwater line and the consequent acceleration of a slug of water which, upon impact within the piping system., causes undue stresses in the piping and its support system.
The significence of these events varies from plant to plant. A total loss of feedwater could affect the ability of the plant to cool down after a reactor shutdown; therefore, the NRC is concerned about these events occurring, even though an event with potentially serious consequences is unlikely to happen.
Because of the continuing o.currence of water ha=er events, the NRC, in September 1977, informed all PWR licensees that water hamer events due to the rapid condensation of steam in the feedwater lines of steam generators represented a safety conce n and that further actions by licensees for Westinghouse and Combustion.ngineering designed nuclear r
steam supply systems are warranted to assure that an acceptably low risk tr public safety due to such events is maintained. Accordi ngly, -
these' licensees were requested to submit proposed hardware and/or procedural modifications, if any, which would be necessary to assure that the feedwater lines and feedrings remain filled with water during normal as well as transient operating conditions.
At the same time, the NRC,provided each PWR licensee with a copy of its consultant's report, "An Evaluation of PWR Steam Generator Water Hammer," NUREG 0291.
The five operating power units considered in this safety evaluation include Kewaunee, Point Beach Units 1 and 2, and Prairie Island Units 1 and 2.
These five units have a particular arrangcment of main feedwater piping that apparently is not susceptible to steam generator water hammer.
Although they have been subjected to system transients that affect the thermal and hydraulic conditions in the feedwater lines and feedwater rings, these units have experienced no steam generator water hammer.
2.0 EVALUATION Our consultant, EG&G, Idaho, Inc. prepared evaluations of steam generator water hammer at Kewaunee, Point Beach 1 and 2 and Prairie Island 1 and 2 as part of our technical assistance program.
Three individual evaluations (references 4.4.1, 4.4.2 and 4.4.3) were prepared separately for each of the three power stations and the conclusion was reached in each case that the means to reduce the potential for water hammer were inadeouate to maintain sufficiently full feedrings and feedwater piping until feedring recovery occurs.
However, these systems have been subjected to the conditions conducive to water han er and no water ham er nas occurred.
Therefore, the potential for steam cenerator water hammer at these three power stations was reevaluated (reference 4.4.4) based en tneir record of success #ul operation and the : articular arrangement of au),iiiary feecwater piping in relation tc main feec. vater piping that is coren to all tnree pewer stations.
The results of that integrated 1086 2i7 7"
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reevaluation showed that since these nuclear power units had been subjected to those. conditions conducive to water hammer that might be expected during
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normal operation, transient or accident conditions and no water hamer had occurred, water hanner is not likely to occur at these units ~
in the future.
Our consultant concluded that steam generator water hammer is not likely to occur in these 5 units during normal or transient operating conditions and recommended that installation of top discharge feedrings in the steam generators to avoid steam generator water hammer is not necessary for continued safe operation of Point Beach Units 1 and 2, Prairie Island-Units 1 and 2 and Kewaunee. Also, our consultant concluded from his integrated reevaluation that, in view of past c'erating experience, the test program recommended in the initial indivicual evaluations is not necess ary.
We have reviewed the licensees' submittals and our consultants reports listed under Section 4 of this evaluation.
We' concur with our consultant's final conclusions and recommendations.
However, even though steam generator water hammer is not likely to occur in these units, these licensees should be vigilant and monitor for water hammers that might impose significant stresses on the piping systems or their supports. We previously requested in our letter of September 2,1977, that licensees for operating pressurized water reactors report all damaging water hammer events occurring in safety related systems or occurring in other systems that affect safety related systems.
A damaging water hammer was defined therein as an event that resulted in damage to pipe supports or pipe insulation; pipe displacement; or failure of pipes or components.
We will continue to monitor licensee event reports as well as water hammer reports frem these licensees for indications of possible water hamer.
If such indications appear in the future, this matter will be reexamined and may result in additional requirements to reduce the probability of steam generator water hammer at these facilities.
3.0 CONCLUSION
Based on our knowledge of water hammer phenomena and our review of the referenced technical evaluation reports by our consultant, the licensee's responses listed in Section 4 and the particular piping geometry and operating history of these five nuclear power units, we have concluded that steam generator water hammer is not likely to occur at these units during normal operation or as a result of transient or accident conditions.
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We, therefore, find that modificaticns to prevent steam generator water hammer are not necessary for the continued safe operation of the Kewaunee, Point Seacn Units 1 and 2 and Prairie Island Units 1 and 2 nuclear power s ta ti ons.
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4.0 REFERENCES
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4.1 Kewaunee 4.1.1 E. W. James, Wisconsin Public Service Corporation (WPSC), letter to R. A. Purple, NRC, Subject
" Response to May 13,1975 NRC letter on Steam Generator Water Ham er",' August 1,1975.
4.1.2 E. W. James, WPSC, letter to R. A. Purple, NRC, Subject -
" Transmittal of report entitled, ' Water Hamer Analysis for Feedwater and Steam Generator Systems'", dated March 10, 1976.
4.1.3 E. W. James, WPSC, letter to A. Schwencer, NRC, Subject -
" Response to September 2,1977 NRC letter on Steam Generator Water Hammer", February 3,1978.
4.2 Point Beach Units 1 and 2 4.2.1 S. Burstein letter to G. Lear, Subject
" Response to May 15, 1975 NRC letter on Steam Generator Water Ham er," June 19, 1975.
4.2.2 S. Burstein letter to G. Lear, Subject
" Response to September 2, 1977 NRC letter on Steam Generator Water Hammer," November 1,1977.
4.3 Prairie Island Units 1 and 2 4.3.1 L. O. Mayer, Northern States Power Company (NSPC), letter to D. Ziemann, NRC, Subject
" Response to May 12, 1975 flRC letter on Steam Generator Water Hammer", September 2,1975.
4.3.2 L. O. Mayer, NSPC Letter to V. Stello, NRC, Subject
" Transmittal of report entitled ' Analysis of PWR Secondary System Fluid Flow Instability'", January 29, 1976.
4.3.3 L. O. Mayer, NSPC, letter to Director of Nuclear Reactor Regulation, NRC, Subject
" Response to September 2,1977 NRC letter on Steam Generator Water Hammer", December 30, 1977.
4.3.4
'W. E. Bennett, Waterhammer in Steam Generator Feedwater Lines, Westinghouse Technical Bulletin, "SD-TB-75-7, June 10,1975.
4.0 Consultant; EG&G. Idano. Inc.
4.4.1 J. A. Dearien letter to R. E. -
ier. JA:-122-79, Point Beach cnits 1 anc 2 Stea-Generator. :er -a-er Technical Evaluation (A5257), Jur.e 12, 1979.
4.4.2 J. A.
Dearien letter to R. E. Tiller,
JA:-129-79.. Kewaunee Ocner Station Stea-Generator Water -ar er Technical Evaluation (A5257), June 12, 1979.
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. 4.4.3 J. A.
Dearien letter to R. E. Tiller,
JAD-135-79, Prairie Island Power Station Steam Genet stor Water Han,er Technical Evaluation (A6257), June 27, 1979.
4.4.4 J. A.
Dearien letter to R. E. Tiller,
JAD 162-79 Reevaluation of Steam Generator Water Hamer for Point Eesch Units 1 and 2 Prairie Island Units 1 and 2, and Kewaunse, Aucust 6,1979.
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