ML20003A281
| ML20003A281 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/29/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, SQRD-50-328-81, NUDOCS 8102030410 | |
| Download: ML20003A281 (3) | |
Text
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'JI VALLEY AO~
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'400 Chestnut Street Tower II January 29, 1981 SQRD-50-328/81-10 Hr.Jamesk.O'Reilly, Director Office of Inc,pection and Enforcement U.S. Nuclear gulatory Commission Region II - Sui 3100 101 Marietta Stre Atlanta, Georgia 03
Dear Mr. O'Reilly:
SEQUOYAH NUCLEAR PLANT UN T 2 - CORROSION OF CARBON STEEL PIPING -
SQRD-50-328/81 FIRST INTERDI REPORT The subject deficiency was initially reported to NRC-OIE Inspector F. S. Cantrell on December 30, 1980, in accordance with 10 CFR 50.55(e) as NCR SQN NEB 8035. Enclosed is our first interin report. We expect to submit our next report by April 8,1981. This NCR has also been reported for Watts Bar and Bellefonte Nuclear Plants.
If you have any questions concernind this matter, please get in touch with D. L. Lambert at FTS 657-2581.
l Very truly yours, TENNESSEE VALLEY AIRECRITY L. M. Mills, Manager Nuclear Regulation and Safety Enclosure
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cc:
Mr. Victor Stello, Jr., Director (Enclosure)V Office of Inspection and Enforcement
/f U.S. Nuclear Regulatory Commission j
Washington, DC 20555 3
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ENCLOSURE SEQUOYAH NUCLEAR PLANT UNIT 2 WATTS BAR AND BELLEFONTE NUCLEAR PLANTS UNITS 1 AND 2 CORROSION OF CARBON STEEL PIPING SQRD-50-328/81-10 WBRD-50-390/8;-10, WBRD-50-391/81-09, BLRD-50-438/81-07, BLRD-50-439/81-07 10CFR50.55(e)
FIRST INTERIM REPORT Description of Condition It has been found that the original criteria for the use of carbon steel piping in raw water syste=s at TVA nuclear plants may not be adequate. Corrosion has been found to cause greater than predicted pressure drops when pipes are sized according to standard industry practice. In addition, the corrosion can cause a thinning of the pipe wall which may not have been accounted for in the design of the a
systems. This condition could affect all raw water systems with carbon steel piping, much as the ERCW System, High Pressure Fire Protection System, ano the pump room and oil c~ooler's for the centrifugal charging pumps, the safety injection pumps, and the containment spray pumps. Also, most electrical board and room air-conditioning units use carbon steel piping.
The problem of corrosion has been the subject of considerable study at TVA. Attached is a brief history of TVA's investigation of this matter.
Recently, NCR 2849 reported that the half-inch prelube lines to the ERCW pump bearings and the 1/2-inch cooling water lines for the ERCW pump motor thrust bearing coolers at Watts Bar Nuclear Plant were found to be severely.
-corroded. These lines were later cut up and nowhere was corrosion found to completely block the pipe. It has not been determined whether or not these 1/2-inch lines were capable of passing the design flow. However, they should have been changed to stainless steel as previously recommended. The recommended changes for Sequoyah were identified in a memorandum dated January 4, 1978. That memorandum contained a statement that the same changes should also be made at Watts Bar. The Sequoyah ERCW pumps did not require bearing prelube and the motor thrust bearing cooler line was already stainless steel. This subtle difference between the two plants was not recognized and, thus, the 1/2-inch lines at Watts Bar were overlooked.
Corrective Action TVA is presently reevaluating all raw water systems for all TVA nuclear plants to identify any changes that are needed. Some of the possible alternatives'are: (1) replacement of existing carbon steel pipes with stainlessIsteel or. larger diameter carbon steel' pipes, and (2) coat the inside of existing pipes with cement in order to inhibit corrosion.. Surveillance testing has been and will be considered as an acceptable alternative to making the recommended changes until the changes are made or until the systems fail to meet test acceptance criteria.
s
i ATTACHMENT A Brief History of TVA's Investigation of Corrosion of Carbon Steel Piping While preoperational testing the Emergency Equipment Cooling Water (EECW)
System at Browns Ferry Nuclear Plant during the summer of 1976, certain heat exchangers were found to be receiving inadequate cooling waterflow because of a buildup of corrosion products in the interior of the carbon steel piping servicing the equipment. A study was undertaken to determine the pervasiveness of this problem in the TVA system and to develop reco== ended practices to mitigate its effects in the design of future steam plants.
Phase I of the study included the removal and analysis of 13 piping samples from eight fossil and nuclear plants. The condition discovered at Browns Ferry was found to be widespread, and in an internal TVA report dated November 3,1977, further investigation was recommended.
The Phase I investigation did not include any actual pressure drop measurements. However, as a result of inspecting the samples taken, an interim criteria for calculating pressure drop was adopted. This criteria was applied to all subsequent calculations for pressure drop in carbon steel raw water piping. The Essential Raw Cooling Water (ERCW) Systems of the Sequoyah, Watts Bar, and Bellefonte Nuclear Plants were reanalyzed, and GE was advised to use this interim criteria in designing Hartsville and Phipps Bend Nuclear Plants' STRIDE piping. The reanalysis identified two specific proble=s:
(1) insufficient flow in some loops in the "new" condition because of a design analysis error and (2) the potential for future reduction in flow because of corrosion. The first problem was initially reported to NRC on Sequoyah and Watts Bar as NCR's 71D and 1003 on November 16, 1977, and January 23, 1978. The final reports on these NCR's were submitted from J. E. G111 eland to J. P. O'Reilly on April 3, 1978, and March 31, 1978. In addition, selective changes were recommended for each plant, and all STRIDE EWS piping and valves two inches and less in.
size were changed to stainless steel.
The interim criteria adopted was purely a matter of judgment, and changes were recommended as a matter of prudence to increase operating margins.
I=plementation of these recommendations is not essential before fuel l
loading since the flow-passing capability of these systems is demonstrated by preoperational tests, and, for an operating plant, a surveillance program to monitor the capability of the system can be used. Such a surveillance program is currently in effect at Browns Ferry Nuclear Plant.
Phase II of the study included the removal and analysis of approximately 40 additional samples and the performance of pressure drop tests on three sections of various sizes of piping at different plants. An empirical correlation was found between the condition of the piping tested and the measured pressure drop. Based on this correlation and the sample data base available, final pressure drop criteria was adopted. The results of both phases of the corrosion study were published in a TVA report dated September 1979 and in the August 1980 issue of Power Engineering Magazine.
On April 30, 1980, TVA issued a revision to the EN DES Design Guide No. DG-M3.5 entitled " Pressure Drop Calculations for Raw Cooling Water Piping."
This revision requires new equations to be used to calculate the friction head loss in carbon steel raw water piping based on the final results of the corrosion study.
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