ML17300A717
| ML17300A717 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 03/27/1987 |
| From: | Haynes J ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 161-00107-JGH-B, 161-107-JGH-B, GL-85-02, GL-85-2, NUDOCS 8704030187 | |
| Download: ML17300A717 (16) | |
Text
Ii'EGULATOR NFORNATION DISTRIBUTION TEN (RIDS)
ACCESSION NBR: 8704030187 DOC. DATE: 87/03/27 NOTARIZED:
NO FACIL:STN-50-528 Palo Vev de Nucleav'tationi Unit ii Av izona Publi STN-50-529 Palo Vev de Nuclear Station.
Unit 2i Arizona Publi STN-50-530 Palo Verde Nuc.leav Stationi Unit 3> Arizona Pub 1 i AUTH. NA>lE AUTHOR AFFILIATION HAYNES> S. Q.
Arizona Nuclear Power ProJect (formerly Arizona Public Serv RECIP. NANE RECIPIENT AFFILIATION Document Contv'ol Branch (Document Control Desk)
SUBJECT:
Fov wards reYised responses to Item
- 1. a of NRC. 8504'17 Generic Ltv'5-02 v e prevention 5 detection of loose parts on secondav g side of steam generators.
DISTRIBUTION CODE:
A058D COPIES RECEIVED: LTR ENCL SI ZE:
TITLE:.OR/Licensing/Genev ic Submittal:
Steam Qenev atov Tube Integritg (l4ater NOTES: Standav dized plant. N. Davisi NRR: 1Cg.
Standav'dized plant. N. Davisi NRR: 1CM.
Standav'dized plant. N. Davisi NHR: 1Cg.
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U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Arizona Nuclear Power Project P.o. BOX 52034
~
PHOENIX, ARIZONA85072-2034 March 27, 1987 161-00107 AJGH/BJA
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2 and 3
Docket Nos.
STN 50-528 (License No. NPF-41)
STN 50-529 (License No. NPF-51)
STN 50-530 Revised
Response
'File: 87-A-056-026
References:
(1)
NRC Generic Letter 85-02 dated April 17, 1985.
Subject:
Staff Recommended Actions Stemming from NRC Integrated Program for the Resolution of Unresolved Safety Issues Regarding Steam Generator Tube Integrity.
(2)
Letter from E.
E.
Van Brunt, Jr.,
- ANPP, to H.
L.
Thompson, Jr.,
- NRC, dated June 21, 1986 (ANPP-32869).
Subject:
Response
Dear Sirs:
The NRC Staff issued recommended actions concerning steam generator tube integrity in Reference (1).
The ANPP response to Generic Letter 85-02 is given by Reference (2).
The purpose of this letter is to revise the ANPP response to item l.a of Generic Letter 85-02.
Item l.a concerns the prevention and detection of loose parts on the secondary side of the steam generators.
This letter revises the response to Item l.a as a result of the experience that ANPP has gained during the recent outage to inspect the PVNGS Unit 1 steam generators.
If you have any questions on this matter, please contact Mr.
W.
F.
Quinn of my staff.
Very truly yours, J.
G. Haynes Vice President Nuclear Production JGH/BJA/rw Attachment P 8704030187 870327 PDR ADDCR 08000828 R
PDR cc:
0.
M. De Michele (all w/a)
E. E.
Van Brunt, Jr.
G.
W. Knighton E.
A. Licitra R.
P.
Zimmerman J.
B. Martin A. C. Gehr
f.
NRC UESTION l.a:
PREVENTION AND DETECTION OF LOOSE PARTS INSPECTIONS Visual inspections should be performed on the steam generator secondary side in the vicinity of the tube sheet, both along the entire periphery of the tube bundle and along the tube lane, for purposes of identifying loose parts or foreign objects on the tube sheet, and external damage to peripheral tubes just above the tube sheet.
An appropriate optical device should be used (e.g.,
mini-TV camera, fiber optics).
Loose parts or foreign objects which are found'hould be removed from the steam generator. 'ubes observed to
'have visual damage should be eddy current inspected and plugged if found to be defective.
These visual inspections should be performed:
(1) for all steam generators at each plant at the next planned outage for" eddy current
- testing, (2) after any secondary side modifications, or repairs, to steam generator internals, and (3) when eddy current indications are found in the free span portion of peripheral
- tubes, unless it has been established that the indication did not result from damage by a loose part or foreign object.
For PWR OL applicants, such inspections should be part of the preservice inspection.
For steam generator models where certain segments of the peripheral region can be shown not to be accessible to an appropriate optical
- device, licensees and applicants should implement alternative actions to address these inaccessible
- areas, as appropriate.
Licensees should take appropriate precautions to minimize the potential for corrosion while the tube bundle is exposed to air.
The presence of chemical species such as sulfur may aggravate this potential, and may make exposure to the atmosphere inadvisable until appropriate remedial measures are taken.
ANPP RESPONSE The PVNGS design incorporates the use of the Combustion Engineering System 80 steam generators.
These steam generators were designed with an integral economizer section on the cold leg half of the tube bundle to preheat the incoming feedwater to saturation conditions.
In order to form the economizer section, it was necessary to install a divider plate to separate the hot leg half of the tube bundle from the cold leg half.
The divider plate is approximately 2-5/8 inches thick and is installed in what is commonly referred to as the tube lane between the hot and cold leg sides of the tube bundle.
This leaves a clearance of approximately 3/4 inches between the divider plate and the tube bundles.
An additional feature of the System 80 steam generator design is that two, 6 inch handholes are provided for access to the secondary side of each steam generator.
The first handhole is located on the cold leg side and is approximately 76 inches above the tube sheet.
This location is between the first and second eggcrate tube supports.
Due to the elevation of this handhole (i.e.,
above the first eggcrate tube support),
a fiber optics inspection of the cold leg tube sheet region can not be conducted from this location because the inspection instrument would be blocked by the eggcrate tube support.
The second
t I
handhole is located on the hot leg side of the steam generator at an elevation just above the flow distribution plate.
Additionally, due to the presence of the divider
- plate, the second handhole is offset 15 degrees from the tube lane.
A fiberoptics inspection of the tube sheet area can not be conducted from the second handhole location due to the fact that the handhole is located above the flow distribution plate and there is no way to access the tube sheet from above the flow distribution plate.
The fiberoptics inspection of the tube bundle periphery is limited to approximately 7 inches in either direction from the second handhole location due to the limitations of the fiberoptics instrument.
- Thus, the design of the System 80 steam generators and the limitations of the fiberoptics inspection equipment are such that visual inspections of the steam generator secondary side along the tube lane and around the periphery of the tube bundle (both at the elevation of the tubesheet) can not be conducted.
Only a small region along the periphery of the tube bundle at the second handhole location (flow distribution plate elevation) can be visually inspected.
Please refer to Figures 1 through 3 for simplified figures of the System 80 steam generators.
At PVNGS Unit 1, fiberoptics inspections were conducted on several occasions to locate any possible loose parts.
These fiberoptics inspections were limited to the region around the second handhole location at the flow distribution plate elevation.
The fiberoptics inspections that were conducted did not show any significant debris or loose parts, nor any visual damage to steam generator tubes.
The previous ANPP response to Generic Letter 85-02 stated that the PVNGS Units 2
and 3
steam generators would be visually inspected in a similar manner as the Unit 1 steam generators.
- However, since the Unit 1
visual inspections have shown that only a
small portion of the steam generators is'ccessible for visual inspections, ANPP has decided that these visual inspections will not be conducted on the PVNGS Units 2-and 3 steam generators.
Generic Letter 85-02 also suggests that licensees should perform secondary side tube sheet visual inspections for the following cases:
(1) for all steam generators at each plant during the next planned outage for eddy current testing, (2) after any secondary side modifications or repairs to steam generator internals, and (3) when eddy current indications are found in the free span portion of peripheral
- tubes, unless it has been established that the indication did not result from damage by a
loose part or foreign object.
As stated previously, only limited secondary side visual inspections are possible on the System 80 steam generators.
Therefore, secondary side visual inspections will only be conducted for those cases where eddy current testing has shown the presence of a potential loose part in an area which is accessible for visual inspections from either of the two handholes.
During the months of January and February,
- 1987, the PVNGS Unit 1 steam generators were subjected to an extensive eddy current inspection.
Over 3,000 tubes were tested in each steam generator and the inspection pattern ensured that all tubes on the periphery of the tube bundle and in the tube lane were inspected.
The eddy current examinations were performed using the standard bobbin coil Zetec MIZ-18 system.
The HIZ-18 utilizes 4
channel multi-frequency (10 KHz to 1
HHz) differential and absolute coil techniques.
The experience gained from this most recent inspection has shown that the multi-frequency eddy current probe can detect the presence of potential loose parts or other anomalies.
The eddy current probe can detect the presence of loose parts that are in contact with or in close proximity to the outside diameter of the tube.
Also, eddy current data can be used
'I II
0to supplement other data that may indicate the presence of a loose part.
Such was the case during the most recent PVNGS Unit 1
steam generator inspections when several dented tubes were observed which suggested the presence of a loose part on top of the flow distribution plate in the tube lane (cold leg side of divider plate).
After observing the dented
- tubes, a rigorous analysis of the eddy current data tended to confirm the fact that a loose part was located close to the dented tubes.
Further evaluation of the potential loose part determined that the part was most likely wedged in this location and was not considered a hazard to continued plant operations.
Therefore, based on the capabilities demonstrated during this recent eddy current inspection, ANPP will use the results of the regularly scheduled eddy current testing (as required by the PVNGS Technical Specifications) to identify potential loose parts in lieu of performing secondary side visual inspections.
Any indications of potential loose
- parts, found during the eddy current examinations, will be evaluated prior to plant restart.
Access for steam generator secondary side modifications and visual inspections can be obtained by using the secondary manway at the moisture separators elevation.
During steam generator secondary side modifications, administrative controls are implemented by the work control program to ensure that loose parts are not introduced into the steam generators.
As an example, the work control program would require strict tool control consisting of logging items into and out of the work area during steam generator secondary side modifications.
ANPP has procedures which specify the steam generator layup requirements necessary to minimize the exposure of the steam generator tubes to air.
A nitrogen blanket is maintained on the secondary side of the steam generators whenever possible.
Additionally procedures are in place to-control the secondary water chemistry within the limits required to minimize corrosion 'of the steam generator tubes.
In conclusion, the system 80 steam generator design does not allow for access to the tube bundle periphery for use of an opti'cal inspection device.
- However, ANPP will implement appropriate alternative actions to aid in the identification of loose parts on the secondary side of the
These alternative actions involve the use of the results from the Technical Specification required eddy current testing to identify loose parts that are either in contact with or in close proximity to steam generator tubes.
I
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FIGURE 1
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