ML20082P284
| ML20082P284 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/03/1991 |
| From: | Shelton D CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9109100267 | |
| Download: ML20082P284 (5) | |
Text
_ _ _ _.
CENTERDOR ENERGY Donald C. Shehon 300 Madison Avenue Vce President Nudcar Toledo, OH 436520001 Davis Besse (419)249 2300 Docket Number 50-346 License Number NPF-3 Serial Number 1978 September 3, 5.991 United States Nuclear Regulatory Cemmission Document Control Desk Vashington, D.C.
20555
Subject:
Request for P.elief frcm ASME Code Section XI to Permit Machine Velding of Steam Generator Tube Plugs at the Davis-Besse Nuclear Power Statiun Gentlemen:
Pursuant to 10 CFR 50.55a(g)(5)(iii), enclosed Js a request for rellet from Section XI of the 1986 edition of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. Relief is requested from the requirements of Section XI, Article IVB-4400, Heat Exchanger Tube or Tubesheet Bore llole Plugging.
Relief is requested to permit machine velding of a velded steam generator tube plug at the Davis-Besse Nuclear Power Station (DBNPS) during the seventh refueling outage (7RFO) which commenced on August 30, 1991.
An explosive velded steam generator tube plug in the hot leg side of the number 2(A) steam generator is to be backed up by a second velded plug.
The explosive velded plug being backed up is suspected of being responsible for the small primary to secondary leak which existed during the last cycle of operation. The suspect plug is fabricated from Inconel 600 material.
Babcock & Vilcox Nuclear Services Compar y (bVNS) informed Toledo Edison that similar plugs installed at other plants have been subject to primary water stress corrosion cracking (PCCC). Other velded plugs of this type installed at the Davis-Besse Nuclear Power Station are being backed up with rolled mechanical steam generator tube plugs during the 7RFO.
However, th's particular velded plug cannot be backed up with a mechanical plug because there is insufficient tube length remaining and, accordingly, a velded plug vill be installed. The velded plug is being fabricated from ER-NI-CR3-SFA-S.14 (INCO S2) material which has proven to be resistant to PVSCC in this application.
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Clevelona Elecinc lituminchng Toledo Edison gj
p Docket Number 50-346 License Number NPF-3 Serial Number.1978-Page 2 Toledo Edison I.as contracted ABB/ Combustion-Engineering (CE) to perform steam generator inspections and steam generator tube plug installations scheduled for the 7RFO.
As noted above, in~ addition to the installation of several mechanical rolled steam generator tube plugs, a single velded plug in the number 2(A) steam generator is to be backed up with a velded plug.
CE plans to use machine velding to veld the back up plug in place.
Machine velding the plug vill minimize radiation dose to workers.
Manual velding of the plug would involve a radiation dose of approximately one person-Rem.
During review of the CE velding procedures, which-first became available for Toledo Edison review on August 22, 1991, questions were raised regarding the sanctioning of machine velding of steam generator tube-plugs by the 1986 and earlier editions of the ASME Code.
As required by 10 CFR 50.55a, the DBNPS Inservice Inspection Program, which governs repairs and replacements, references the 1986 edition of the ASME Code. The 1986 edition is the most recent edition of the ASME i
I Code currently approved by the NRC in 10 CFR 50.55a(b).
The 1986 and earlier editions of Section XI of'the ASME Code, Article IVB-4410, require that steam generator tube plugging be in accordance vith IVB-4420 or IVB-4440.
IVB-4420 addresses explosive velding of l
steam generator tube plugs.
IVB-4440 addresses manual velding of steam generator tube plugs. Hachine velding of tube plugs is not addressed.
After discussions with CE, the Authecized Nuclear Inservice Inspector (ANII) and the Authorized Inspection Agency (AIA), on August 30, 1991, i
Toledo Edison concluded that there is no avenue available within the NRC endorsed editions of the ASME Code which sanctions machine velding of the replacement steam generator tube plug.
The alternatives of not installing or manual velding the back up plug are undesirable, Manual velding would incur unnecessary radiation exposure and is inconsistent with the principle of maintaining radiation dose as-low-as-reasonably-achievable.
Backing up the plug is desirable from the standpoint of maintaining a high degree of steam i
generator tube integrity.
Accordingly, Toledo Edison has opted to request NRC approval of relief from-tne requirements of Section XI, Article IVB-4410 of the 1986 edition o.
ASME Code.
The relief request
[
is enclosed.
I Toledo Edison notes that beginning with the 1986' addenda, Sectio.. XI, Article IVB-4430, Tube or Tubesheet Hole Plugging by Fusion Velding, was added.
IVB-4430 addresses' requirements for machine velding of tube plugs. The-relief request vould adopt these requirements as an alternative to IVB-4410 of the 1986 edition of the ASME Code.
Toledo Edison believes that there are nu technical isrues related to approval of this alternative since the NRC has proposed a revision to 10 CFR
~
50.55a to endcrse ASME Code editions and addenda through the 1989 e
edition (56FR3796 dated January 31, 1991). No restrictions on the use j
e s
Docket Number 50-346
[
License Number NPF-3 Serial Number 1978 Page 3 of IVB-4430 vere indicated in the proposed rule.
Therefore, Toledo Edison concludes that adoption of the requirements IVB 4430 of a later Code edition (1986 edition,ith addenda through 1988 and the 1989 edition), provides an acceptable level of quality and safety.
Toledo Edison requests NRC approval of the enclosed relief request by September 20, 1991, the scheduled date for installation of the back up velded plug.
If you have any questiens regarding the relief request, please contact Mr. R. V. Schrauder, Manager - Nuclear Licensing, at (419) 249-2366.
Very truly yours,
/ he k dC)l[
i
PVS dli Attachment i
i cc:
P.
M.
Byron, NRC Region III DB-1 Senior RerJdent Inspector A.
B.
Davis, Regional Administrator, NRC Region III J.
B.
Ilopkins, NRC/NRR DB-1 Senior Project Manager Utility Radiological Safety Board e
s i
Docket Number 50-346 License Number MPF-3 Serial Number 1978 Attachment Page 1 RELIEF REQUEST Request for Relief from ASME Code Section XI, Article IVB-4410, to Permit Machine Velding of Steam Generator Tube Plugs.
Componeat Description Once Through Steam Generator Tubes ASME Code Class ASME Section III, Class A - 1968 Edition through summer 1968 Addenda
Applicable Code Requirement
Section XI of the 1986 edition, Article IVB-4410 states:
"lieat exchanger tube or tubesheet bore hole plugging shall be in accordance with the rules of IVB-4420 or IVB-4440."
IVB-4420 addresses explosive velding of steam generator tube plugs.
IVB-4440 addresses manual welding of steam generator tube plugs.
Machine velding of steam generator tube plugs is not sanctioned by the 1986 or earlier editions of Section XI.
Statement of Reques*.ed Relief Relief is requested from the IVB-4410 requirement to explosively veld or manually veld steam generator tube plugs in accordance with the rules of IVB-4420 or IVB-4440, respectively.
Basis for Requested Relief During the seventh refueling outage (7RFO), an explosive velded steam generator tube plug in the hot leg side of the number 2(A) steam generator is to be backed up by a second velded plug.
The explosive velded plug being backed up is suspected of being 4
responsible for the small primary to secondary leak which existed during the last cycle of operation. The suspect plug is fabricated from Inconel 600 material.
Babcock & VJ1cox Nuclear Services Company (BVNS) inforned Toledo "dison that similar plugs installed at other plants had been subject to primary water stress corrosion cracking (PVSCC).
Other velded plugs of this type installed at the Davis-Besse Nuclear Power Station are being backed up vith rolleo mechanical steam generator tube plugs.
However, this particular velded plug cannot be backed up with a mechanical plug because there is insufficient tube length remaining and a velded plug vill be installed. The velded plug is being fabricated from ER-N1-CR3-SFA-5.14 (INCO 82) material.
Machine welding is to be used to veld the back up plug in order
+4 G
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Docket Number 50-346-
_ License Number NPP-3 3
Cerial Number 1978 Attachment Page 2-to maintain radiation exposure to workert; as-low-as-reasonably-
- achievable. -Manual velding of the plug would involve a radiation dose of approximately one' person-Rem.
The alternatives of not installing or manual velding the back up plug are undesirable.
Manual valding would_ incur unnecessary radiation exposure and is inconsistent with the. principle of maintnining radiation dose as-lov-as-reasonably-achievable.
Backing up the plug is desirable from the standpoint of maintaining a high degree of steam generator tube. integrity.
Proposed Alternative Requirements Machine velding of tube plugs vill be performed in accordance with the requirements of Section-XI Article IVB-4430, Tube or Tubesheet Hole Plugging by Fusion Velding, incorporated in the 1986 addenda and subsequent editions of_the ASME Code. The NRC has proposed a revision to 10 CFR 50.55a to endorse ASME Code editions and addenda through the 1989 edition (56FR3796 dated January 31, 1991). No restrictions on the use of IV3-4430 vere indicated in the proposed rule.
Therefore, Toledo Edison concludes that adoption of the requirements of IVB-4430 of a-
.later Code edition (1986 edition with addenda through 1988 and the 1989 edition), provides an acceptable level of quality and safety.
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