ML20248A637
| ML20248A637 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 09/22/1989 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8910020270 | |
| Download: ML20248A637 (5) | |
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m2mn2ss September 22, 1989
- U.'S. Nuclear Regulatory Commission Attn:' Document Control Desk Washington, DC 20555
Reference:
Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 B&W Steam Generator Tube Plug Inspections Gentlemen:
.This' letter is in response to your questions regarding our inspection plan for examining B&W steam generator tube plugs installed in our Unit 1 steam generators.
These questions were the result of a
conference call on September 12, 1989 between Mr. Keith Wickman,- Mr.
Herb Conrad, and Mr. Peter Tam of the NRC and Mr. Steve Sovick of our Licensing Section.
Question 1:
Provide the heat numbers of any potential replacement plugs.
Response
Any plugs installed during the seventh refueling outage will be manufactured from Inconel 600 having a
microstructure which exhibits optimum resistance to primary water stress corrosion cracking (PWSCC).
These B&W designed plugs are fabricated from heats 4989-4 and 7042-2 with microstructure characterized and demonstrated to be satisfactory.
Question 2:
Consider replacing the older B&W plugs during this seventh refueling outage regardless as to whether crack indications are identified.
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4 B,eavbr'Vallcy Pow ~r Station, Unit No. 1 W%
. Docket No.-50-334, License No. DPR-66 B&W: Steam Generator. Tube Plug Inspections Page 2 is 4
Response
Our. plan' is to replace only those plugs having crack indications,
'since field experience indicates that heel cracking significantly precedes toe cracking.
No toe cracking has been revealed in the field to date.
In
- addition, stress analysis of the heel and toe transition-shows the maximum tensile stresses to be in the axial direction for the heel transition and in the hoop direction for the toe transition.
- Thus, circumferential cracking is postulated for heel transitions and axial cracking for toe transitions.
Circumferential cracking at the toe transition is necessary for plug top release in a B&W designed plug.
Plug heel release resulting from circumferential cracking initiated following the seventh refueling outage inspection is considered unlikely.
Field experience shows that none of the circumferential cracks in the heel transitions have propogated throughwall.
Stress analysis again supports this field observation since there is a high compressive stress on the plug outside diameter tending to counteract the tensile stresses necessary for crack propagation.
Therefore, installed Inconel 600 plugs not revealing crack indications during the seventh refueling outage inspection can remain in service for at least one additional fuel cycle until replacement with an improved Inconel 690 plug is possible.
B & W also supports this position.
Question 3:
In the event there are no crack indications identified during our inspection, consider removing an older plug or two for the purpose of laboratory verification that no crack indications exist.
Response
The equipment required for plug removal would not be set-up in the event there are no crack indications.
If crack indications
- exist, it will be necessary to perform additional equipment change-out and set-up in order to accomplish plug removal.
This activity results in significantly increased personnel radiation exposure.
It is our intent to keep radiation exposure as low as reasonably achievable, therefore, we would not implement a plug removal effort to remove an older vintage plug if no cracks are indicated.
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B.enver Valley Powsr Station, Unit No. 1 L
Docket No. 50-334~, License No. DPR-66' B&W Steam Generator. Tube Plug Inspections 1
Page 3
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- However, we will remove an older vintage plug for 4
laboratory verification if removal equipment set up is required to remove other plugs with crack indications.
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Question 4:
What is our schedule for inspecting the B&W steam generator tube plugs?
Response
Plug inspection is scheduled to commence the week of September 25,
- 1989, and conclude the week of October 23, 1989.
Question 5:
Provide a
breakdown of the various B&W steam generator tube plug heat numbers which are currently installed.
Response
Attached as Table 1
is a breakdown of the presently installed B&W plugs in the Unit No. 1 steam generators by heat number.
These responses detail certain aspects of our plan to address the B&W steam generator tube plugs.
The following provides a brief summary of our inspection and remedial action plan for Unit No. 1 steam generators with B&W designed Inconel 600 rolled tube plugs.
All B&W designed plugs installed on the hot leg side of the steam generators will be inspected by utilizing a rotating pancake coil eddy current technique.
Any plugs with crack indications will be replaced with an Inconel 600 plug.
All cold leg plugs will be inspected utilizing the same eddy current technique in those channel heads where inspection equipment is installed for reasons other than plug inspection.
Changes to robotic manipulator equipment will not be made to gain access to a small number of plugs provided no other initially accessible plug reveals crack indications upon I
examination.
If any cold leg plug reveals crack indications, all cold leg plugs will be inspected regardless o f' previous access constraints.
Any cold leg plugs revealing crack indications will be replaced with an Inconel 600.
The rotating pancake coil eddy current technique is proven to provide a
conservative assessment of installed plug cracking.
If PWSCC is detected during inspection, all affected plugs will be removed.
This will permit a subsequent systematic replacement of all B&W Inconel 600 plugs with the presently unavailable B&W Inconel 690 plug (which exhibits superior PWSCC resistance) at future outages.
Replacement in this manner will minimize personnel radiation exposure by negating the need to perform multiple plug removals and replacements at the same tube location.
L
.,B.env0r Vallcy Powar Station, Unit No. 1 a
hi Docket No. 50-334, License No. DPR-66 B&W Steam Generator Tube Plug Inspections Page 4 If you have.any questions regarding this information, please contact me or members of my staff.
Very truly yours, r
D. Sieber ice President Nuclear Group cc:
Mr. J.
Beall, Sr. Resident Inspector Mr. W. T. Russell, NRC Region I Administrator Mr.
P. Tam, Sr. Project Manager l
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