ML13330A045
| ML13330A045 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/22/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13330A044 | List: |
| References | |
| TASK-05-13, TASK-5-13, TASK-RR NUDOCS 8005120116 | |
| Download: ML13330A045 (4) | |
Text
OSURE 80 05120//(o U.S.
NUCLEAR REGULATORY COMMISSION SAFETY EVALUATION REPORT STEAM GENERATOR WATER HAMMER SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1 DOCKET NO. 50-206 APRIL 1980
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 significance of these events varies from plant to plant. Since a total loss of feedwater could affect the ability of the plant to cool down after a reactor shutdown, the NRC is concerned about these events occurring, even though an event with potentially serious consequences is unlikely to happen, Because of the continuing occurrence of water hammer events, the NRC, in September 1977, Informed all PWR licensees that water hammer events due to the rapid condensation of steam in the feed water lines of steam generators represented a safety concern and that further actions by licensees for Westinghouse and Combustion Engineering designed nuclear steam supply systems are warranted to assure that an acceptably low risk to public safety due to such events is maintained. Accordingly, 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, Three water hammer events have occurred at San Onofre Unit 1 since it began producing power in 1967. These events are associated with damage to a feedwater regulating valve and some piping supports.
It cannot be determined with certainty whether these water hammer events were steam generator water hammer events as described in the
-2 introduction or whether they were due to rapid motion of the regulating valve resulting from the malfunctions that occurred in the valve positioners. Based on this experience the licensee has stated that modification of the steam generators is not warranted but that a program will be initiated to evaluate the potential magnitude of Water hammers, define their effects on the components of the feed water system and identify appropriate corrective measures.
2.0 EVALUATION Our Consultant, EG&G Idaho Inc., prepared the attached evaluation of steam generator water hammer at San Onofre Unit 1 as part of our technical assistance program. (Letter from J.A.
Dearien,
EG&G, to R.E. Tiller, DOE, dated March 31, 1980). We have reviewed this report together with the licensee's submittals listed under item
- 40.
We have also reviewed the licensee's program to evaluate the potential magnitude of water hammers, define their effects on components of the feedwater system and identify appropriate corrective measures. We have found that this is a prudent measure to avoid possible damage from water hammer in the future. This program is outlined in the licensee's submittal of February 14, 1980, and is scheduled to be completed by October 1980. We find this schedule acceptable.
Upon completion of this program, we will review the results and determine whether additional corrective measures will be required.
3.0 CONCLUSION
Based on our knowledge of water hammer phenomena, and our review of the licensee's responses_and the enclosed evaluation report, we concur with our consultant's conclusion that the potential for steam generator water hammer is sufficiently low to permit continued operation of this facility, However, even though steam generator water hammer is not likely to occur, the licensee should be vigilant and monitor for water hammers that might impose significant stresses on the piping systems or their supports, In addition, the licensee will carry out a program to evaluate further the potential for damage due to steam generator water hammer at San Onofre Unit 1. We will review the results of that program and monitor reports from this licensee for indications of possible steam generator water hammer, Our review may result in additional requirements to reduce the probability of steam generator water hammer at this facility.
-3 We have concluded that,a damaging steam generator water hammer is not likely to occur at this facility and, therefore, we find no undue risk to the health and safety of the public as a result of the continued operation of the San Onofre Nuclear Generating Station Unit 1.
4.0 REFERENCES
4.1 K.P. Baskin, Southern California Edison Company (SCEC), letter to R.A. Purple, NRC, Subject - "Secondary System Fluid Flow Instability," July 14, 1975.
4.2 K.P. Baskin, SCEC, letter to A. Schwencer, NRC, Subject "Susceptibility to Steam Generator Feedwater Line Waterhammer Events," December 27, 1977.
4,3 J.B. Moore, SCEC, letter to R.H. Engelken, NRC-R/V, Subject "Degraded Conditions of Hydraulic Snubbers," November 6, 1978.
4.4 K.P. Baskin, SCEC, letter to D.L. Ziemann, NRC, Subject "Information Requested on Feedwater Lines," July 3, 1979.
4.5 J.G. Haynes, SCEC, letter to D.L. Ziemann, NRC, Subject "Information Requested Concerning Steam Generator Water Hammer," August 31, 1979, 4.6 D.L. Ziemann, NRC, letter to J.H. Drake, SCEC, Subject "Steam Generator Water Hammer," September 12, 1979.
4.7 K.P. Baskin, SCEC, letter to D.L. Ziemann, NRC, Subject "Steam Generator Water Hammer," February 14, 1980.
4.8 J,A,
Dearien,
EG&GIdaho, letter to R.E. Tiller, DOE, Subject "Steam Generator Water Hammer Technical Evaluation, San Onofre Unit 1," March 31, 1980.
4.9 J.A. Block, et al, An Evaluation of PWR Steam Generator Water Hammer, Creare, Inc. NUREG-0291 (December 1976).
4.10 W,E,.Bennett, Waterhammer in Steam Generator Feedwater Lines, Westinghouse Technical Bulletin, NSD-TB-75-7 (June 10, 1975).
Idaho, Inc.
P. O. Box 1625 Idaho Falls, Idaho 161 March 31, 1980 Mr. R. E. Tiller, Director Reactor Operations and Programs Division Idaho Operations Office -
DOE Idaho Falls, ID 83401 STEAM GENERATOR WATER HA4MER TECHNICAL EVALUATION, SAN ONOFRE UNIT NO. 1 (A6257) -
JAD-80-80 Ref: J. A.
Dearien letter to R. E. Tiller,
JAD-225-79, PWR Steam Generator Water Hammer Reviews (A6257), November 8, 1979
Dear Mr. Tiller:
We have reviewed the operating history of San Onofre Unit No. 1 pertinent to. steam generator water hammer and the related operational and procedural characteristics of the feedwater system. This reviewhas shown that con ditions conducive to steam generator water hammer have been encountered during normal operating transients and startup and shutdown operations.
However, steam generator water hammer has not occurred at this facility although a few feedwater system water hammer events have occurred. It is concluded that the potential for steam generator water hammer is suf ficiently low to permit continued operation of this facility.
This transmittal constitutes completion of the San Onofre Unit No. 1 SER, Node T-12 of the PERT chart for FIN A6257.
All currently scheduled activity under FIN A6257 is also completed with this transmittal.
Very truly yours, John A.
Dearien,
Manager Code Assessment and Applications Program 0CC:bb
Attachment:
As stated cc:
W. i R. W. Kiehn, EG&G Idaho w/o attach.