ML20151Q279
| ML20151Q279 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 08/03/1988 |
| From: | Kuncl L NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-84-11, GL-88-01, GL-88-1, NUDOCS 8808110094 | |
| Download: ML20151Q279 (4) | |
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Nebraska Public Power District August 3, 1988 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555
Subject:
IGSCC in BWR Austenitic Stainless Steel Piping, Generic Letter 88-01 Cooper Nuclear Station NRC Docket No. 50-298 DPR-46
References:
1)
Generic Letter 88-01, dated January 25, 1988, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping" 2)
Generic Letter 84-11, dated April 19, 1984, "Inspections of BWR Stainless Steel Piping" 3)
Letter NPPD to D. G. Eisenhut dated June 4,
- 1984, "Response to Generic letter 84-11" 4)
Letter NPPD to H. L. Thompson, Jr. dated April 30, 1985, "Response to Generic letter 84-11 dated April 19, 1984" 5)
Letter NPPD to NRC dated May 3, 1988, "Inservice Inspection Program" Gentlemen:
Pursuant to the request of Reference 1, the District is submitting the attached information regarding pipe replacement, inspection, leakage detection and other addressed IGSCC concerns.
For clarity in presentation, information is provided for the applicable items stated in Reference 1.
Should you have any questions regarding this information, please call.
Sin erely, 1J L. G.
uncl Nuclear Power Group Manager LGK/gs:rh20/3(12A) cc:
U.S. Nuclear Regulatory Commission Regional Office - Region IV Arlington, Texas NRC Resident Inspector i
j Cooper Nuclear Station t
8808110094 880803 l
PDR ADOCK 05000298 p
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Page 2 August 3, 1988 STATE OF NEBRASKA )
) ss PLATTE COUNTY
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L. G. Kuncl, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this information on behalf of Nebraska Public Power District; and that the statements contained herein are true to the best of his knowledge and belief.
L. 7. Kuncl Subscribedinmypresenceandsworntobeforemethis3nkdayof USb 1988.
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Attachm:nt Pags 1 NPPD Response To Generic Letter 68-01 Item Current plans regarding pipe replacement and/or other measures taken or to be taken to mitigate IGSCC and provide assurance of continued long-term piping integrity and reliability,
Response
During the Fall 1984 outage of Cooper Nuclear Station, the District replaced the Reactor Recirculation system and the ICSCC susceptible portions of the Residual Heat Removal, Core Spray, and Reactor Vater Cleanup systems that were in the scope of Generic Letter 84-11 (Reference 2) with 316NG material.
Recirculation system inlet and cutlet nozzle safe-ends, Core Spray safe ends, and jet pump instrumentation safe-ends were also replaced with 316NG material.
To further mitigate the reoccurrence of IGSCC:
- 1) the piping systems were redesigned to minimize the number of field welds, 2) shop welds were solution heat treated, 3) field weld preparation geometry followed EPRI recommendations to minimize veld induced stress, and 4) weld preparation counterbores were polished to remove machine cold working.
Field welding was closely monitored to control interpass temperatures, heat input and deposition rate and the final weld crowns were ground to improve ISI inspection capabilities.
Since the Cooper Station recirculation and core spray system, and jet pump instrumentation nozzles were originally installed with ICSCC susceptible Inconel 182 buttering, these nozzles were counterbored and clad with Inconel 82 material during safe end replacement.
References 3 and 4 provided additional information regarding the above modifications.
Prior to startup after pipe replacement, induction heating stress improvement was performed on all field welds, including recirculation and core spray safe ends.
In addition, all reactor vessel attachments made of susceptible material with an inside diameter greater than four inches have been replaced with IGSCC resistant material.
The District has no plans to implement hydrogen water chemistry at Cooper Nuclear Station but we will continue to monitor industry developments in this area.
l Item Inse rvice Inspection (ISI) Program.
Response
The Cooper Nuclear Station ISI Program has been updated to include welds in the replacement piping discussed above.
The revised ISI Program pages were part of the addenda package submitted in Reference 5.
As implemented, our ISI Program conforms to the staff positions stated in Reference 1 on inspection schedules, methods and personnel, and sample expansion.
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l Attachment 1
Page 2 It is noted that Generic Letter 88 01 applies to a larger scope of piping than previous staff guidance contained in Generic Letter 84-11.
The previous guidance included thase welds out to the second isolation valve from the reactor coolant pressure boundary.
The scope of Generic Letter 88-01 does not contain this provision and applies to "all BWR piping made of austenitic stainless steel that is four inches or larger in nominal diameter and contains reactor coolant at a temperature above 200'F during power operation regardless of code classification."
This addition in scope will include some Reactor Water Cleanup (RWCU) System piping located outside of primary containment which has not been replaced or has had other measures taken to mitigate IGSCC.
This piping will be added to the Cooper ISI Program so that inspection of all accessible welds will be implemented during the next refueling cutage which is currently scheduled to begin in the Spring of 1989.
The ISI Program for piping covered by the. scope of Reference 1 will be in conformance with the stated staff positions on schedule, methods and personnel, and sample expansion.
This commitment will be incorporated into our ISI Program by including this correspondence in our next ISI revision.
This revision will be forwarded to the staff, per our commitment in Reference 5.
Item Technical Specifications and Leakage Detection.
Response
As discussed above, all susceptable piping inside the drywell, within the scope of Generic Letter 88-01, has been replaced with ICSCC resistant 316NG material.
Additional actions described abova have been performed to mitigate the reoccurrence of IGSCC in this piping.
Based on this, the District does not plan on amending the current CNS coolant leakage Technical Specifications.
Since there are no ICSCC Category D, E, F, or G piping welds inside primary containment, the District will not propose any increased Technical Specification requirements on containment leakage measurement instruments.
Item Notification of NRC
Response
The District will notify the Commission of any identified flaws that do not meet IWB-3500 criteria of Section XI of the Code for continued operation without evaluation.