ML19257A132
| ML19257A132 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 11/28/1979 |
| From: | Counsil W NORTHEAST UTILITIES |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| IEB-79-17, NUDOCS 8001020136 | |
| Download: ML19257A132 (4) | |
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November 28, 1979 Docket No. 50-213_
Mr. B. H. Grier, Director Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406
References:
(1)
B. H. Grier letter to W. G. Counsil dated July 26, 1979 forwarding I&E Bulletin No. 79-17.
(2)
B. H. Grier letter to W. G. Counsil dated October 29, 1979 forwarding I&E Bulletin No. 79-17, Revision 1.
(3)
W. G. Counsil letter to B. H. Grier dated August 24, 1979.
Gen tl emen:
Haddam Neck Plant I&E Bulletin No. 79-17 Reference (1) requested that Connecticut Yankee Atomic Power Company (CYAPC0) con-duct a review of the safety-related stainless steel piping systems to identify systems and portions of systems which contain stagnant oxygenated borated water.
The NRC Staff requested that CYAPC0 provide specific information regarding these systems within thirty (30) days and to examine the systems by visual, liquid pene-trant and ultrasonic techniques within ninety (90) days to verify system integrity.
In Reference (3), CYAPC0 submitted the thirty (30) day response to Items 1(a)-1(d) of Reference (1).
The Reference (3) response identified the systems and portions of systems which CYAPC0 had determined to contain stagnant oxygenated borated water.
In response to Item 2 of Reference (1), CYAPC0 provides the following:
Item 2(al Perform ASME Secticn XI visual examination (IWA 2210) of normally accessible welds of all engineered safety systems at service pressure to verify system integrity.
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.. Response CYAPC0 noted in Reference (3) that guidance for the visual examination to verify system integrity will be drawn from IWA 5240. This guide states that insulation will be removed only if evidence of leakage is found at a low point or under a pipe. This definition was selected as it most appropriately addresses the in-tent of this inspection.
Accordingly, CYAPC0 has performed a visual examination of all normally accessible welds at service pressure in accordance with IWA 5240.
The results of these visual examinations indicate no observed through-wall leakage in any of the systems identified in Reference (3).
Item 2(b)
Conduct ultrasonic examination and liquid penetrant surface examination on a rep-resentative number of circumferential welds in normally accessible portions of systems identified by 1 above.
It is intended that the sample number of welds include all pipe diameters in the two and one-half inch (2-1/2") to twenty-four inch (24") range with no less than a ten percent (10%) sample by system and pipe wall thickness.
It is also intended that the UT examination cover the weld fusion zone and a minimum of one-half inch (1/2") on each side of the weld at the pipe ID.
The examination shall be in accordance with the provisions of ASME Code Section XI-Appendix III and supplements of the 1975 winter addenda except all signal re-sponses shall be evaluated as to the nature of the indications.
These code methods or alternative examination methods, combination of methods, or newly developed techniques may be used provided the procedures yield a demonstrated effectiveness in detecting stress corrosion cracking in austenitic stainless steel piping.
Response
The liquid penetrant (PT) surface examinations have been completed on ten percent (10%) of the welds including all existing pipe diameters in the two and one-half inch (2-1/2") to twenty-four inch (24") range of stagnant oxygenated borated water systems.
The liquid penetrant surface examination was completed in accordance with Section V, Article 6, of the ASME code up to and including the summer of 1975 addenda.
The examination identified no cracking in the welds examined. Ultrasonic examinations have also been completed on ten percent (10%) of the welds including all existing pipe diameters in the two and one-half inch (2-1/2") to twenty-four inch (24") range of stagnant oxygenated borated water systems, with the exception of the six-inch (6") diameter piping in the Residual Heat Removal (RHR) system.
Welds in this size piping system were not ultrasonically examined.
CYAPC0 deter-mined that only liquid penetrant surface and visual examinations would suffice based on the following:
(1) The welds on the six inch (6") diameter piping in the RHR system would require weld preparation grinding before ultrasonic examinations could be performed.
The operability requirements of this system are unique in that it is required for both ECCS recirculation and residual heat removal opera-tions.
Therefore, the RHR system can only be taken out of service when all the fuel has been off-loaded to the spent fuel pool. This will occur during the 1980 refueling outage and inspections and maintenance activities on the RHR system are scheduled.
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.. (2) Ultrasonic examinations on piping welds previous to the six inch (6")
piping revealed no crack indications.
(3)
Initial results from the examinations at Three Mile Island, Unit No.1 (TMI-1) indicated that intergranular stress corrosion cracking (IGSCC) was present on twenty-two percent (22%) of the welds examined after a relatively short period of operation.
It is highly probable that an IGSCC problem at the Haddam Neck Plant would have already been detected previous to these inspections, during the past twelve (12) years of operation, if in fact one existed.
(4)
Item 2(b) of Reference (2) eliminates the requirement to perform the ultrasonic examination on piping with 250 mil wall thickness.
This is in recognition of the fact that through-wall cracking would be eviden+
af ter a period of time in these wall thicknesses if the IGSCC phenomena were present. The six inch (6") diameter schedule 40 pipe at the Haddam Neck Plant has a nominal wall thickness of 280 mil. Therefore, CYAPC0 is justified in eliminating this piping from the ultrasonic examinations based on a slight extension of the Reference (2) relaxation. Additional welds have been examined in the eight inch (8") diameter piping of the RHR system to add further confidence in the UT examination results and in the integrity of the RHR system.
Therefore, the prudent approach involving this examination substitution fulfilled the intent of the Bulletin requirements yet eliminated the need to prepare the welds.
The ultrasonic (UT) examinations have been completed in accordance with Westinghouse UT procedure NS0-ISI-90, Revision 2, which exceeds the requirements of Appendix III,Section XI, and supplements of the 1975 winter addenda.
This Westinghouse procedure which requires examination by both straight beam and angle beam techniques has been qualified on samples at TMI with known intergranular stress corrosion cracking.
No evidence of cracking has been discovered in any of the nineteen (19) welds examined.
In Reference (2), the NRC Staff revised Reference (1) to include systems or portions of systems where dynamic flow conditions do not exist on a continuous basis.
In Reference (3), CYAPC0 defined piping not flushed at least once per month as stag-nant.
This definition is supported by the following considerations:
(1) No cracks were found in the high pressure injection lines at Three Mile Island, Unit No.1 (TMI-1) which were occasionally flushed.
(2) This definition results in examination of a sufficiently large sample of welds to produce a statistically meaningful inspection.
(3) The class of piping is subjected to the more adverse environment with respect to this concern, as the fluid is motionless for the longer period of time than the piping defined as non-stagnant.
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.. CYAPC0 maintains that the definition of stagnant noted above adequately addressed the concerns of Reference (1) based on the following:
(1) The visual examination required by Item 2(a) of Reference (1) has indi-cated no through-wall leakage exists.
(2) Completion of liquid penetrant and ultrasonic examinations on ten percent (10%) of the accessible welds in the stagnant oxygenated borated water systems identified in Reference (3) has not revealed any crack indications.
(3) The chemistry program described in Reference (3) in response to Item 1(b) of Reference (1) assures that impurities are maintained at acceptable levels in the piping systems under consideration.
(4) The weld joint design used at the Haddam Neck Plant differs significantly from that employed at Three Mile Island, Unit No.1.
The geometry of the TMI-l weld joint is judged to incret.se the suscepibility of the subject welds to the IGSCC phentmenon.
(5)
No problems of this nature have been identified at the Haddam Neck Plant during its twelve (12) years of operation.
In addition, the monthly visual examination described in Item 2(a) of Reference (2) will not be performed as the examinations required by References (1) and (2) have been completed under CYAPC0's interpretation.
CYAPC0 has not identified cracking in any of the welds examined at the Haddam Neck Plant by any of the methods re-quired by Reference (1) as revised by Reference (2).
We trust you find this information satisfactory to disposition the Reference (1) and (2) concerns. We remain available should the Staff require clarification of any of the above information.
Very truly yours, CONNECTICUT YANKEE ATOMIC POWER COMPANY
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e W. G. Counsil Vice President 1665 317