ML19347A794
| ML19347A794 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 09/26/1980 |
| From: | Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Clark R, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 794, NUDOCS 8009300255 | |
| Download: ML19347A794 (4) | |
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VIRGINIA EI.ECTRIC AND PowE n CoxrANY Hrctruown,VxuorwrA 2006 September 26, 1980 Mr. Harold R. Denton, Director Serial No. 794 Office of Nuclear Reactor Regulation N0/FHT:ms Attn: Mr. Robert A. Clark, Chief Docket No. 50-338 i
Operating Reactors Branch No. 3 License No. NPF-4 l
Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C.
20555
]
Dear Mr. Denton:
NORTH ANNA POWER STATION UNIT NO. 1 STEAM GENERATOR INSPECTION PORTS I.
Background
North Anna Unit 1 completed its first cycle of operation in September, 1979, and an extensive steam generator inspection was performed during i
the refueling outage.
The results of that inspection were reported in our letter of December 10, 1979, Serial No. 1003, and are summarized briefly here.
-3 Prior to the shutdown, a minor primary-to-secondary leak (about 2 x 10 gpm) was indicated in steam generator (SG) "C".
Extensive eddy current inspections utilizing 7.5,100 and 400 KHz probes were performed on all three SGs.
These inspections identified two leaking tubes in SG "C" and indicated that approximately 34 percent of the tubes inspected in the three SGs were subject to the early stages of the denting phenomenon.
1 Both of the leaking tubes were located in the first row in SG "C",
and as a precautionary measure, all first row tubes were plugged in all three SGs.
Additional corrective actions were implemented including:
- 1) restriction of the use of the Powdex condensate polishers to prevent resin intrusions into the feedwater; 2) institution of a condenser in-leakage abatement pr~ ram; 3) implementation of a new SG chemistry pro-gram; 4) institution of the SG Boric Acid Treatment Program to prevent j
further corrosion; and 5) implementation of a hydrogen monitoring program to judge the effectiveness of the boric acid treatments.
8009300 255 p
Mr. Harold R. Denton 2
VinotwA EttcTaic Ano Powra COMPANY TO Your staff issued a uafety evaluation report on February 4,
- 1980, addressing the SG inspection performed and the corrective actions taken.
It stated that the conservative maintenance and corrective actions implemented were commensurate with the SG inspection results.
Mr.
A.
Schwencer's letter of April 8, 1980, requc.sted us to provide additional information concerning the preliminary results of the newly-implemented feedwater chemistry program.
We provided the requested information in our letter of June 30, 1980, Serial No. 352.
We also forwarded an Operational Background Chemistry Review prepared by NVI Corporation for North Anna Unit 1 by our letter of June. 18, 1980, Serial No. 543.
These documents indicated that the causes of the observed corrosion are various and not attributable to any one factor.
II.
Steam Generator Inspection Ports At the time of our December 10, 1979, inspection report we committed to installing SG inspection ports in all three SGs at your staff's request.
Since that time, we believe that our substantial corrective actions have effectively eliminated the need for installation of the inspection ports at this time. Our reasoning is detailed below.
A.
Boric Acid Treatments Preliminary indications as to the effectiveness of the Boric Acid j
Treatment Program are not yet available. The lack of hydrogen base-line data has hampered Westinghouse's analysis of the hydrogen nioni-toring program.
It is not possible to determine whether or not the corrosive attack has been halted until another inspection an be performed.
The results of this inspection would prove valuaole in assessing the future advisability of installing inspection-~ ports-1 B.
First Row Tubes Plugged f
One of the purposes of the inspection ports was to facilitate removal of tube samples at the U-bend locations.
The plugging of all first row tubes has reduced the immediate need to obtain tube samples.
Indeed, if our corrective actions have been successful (and another inspection is necessary to quantify this) the ports will have been installed needlessly.
C.
Minimize SG Penetrations It is prudent to minimize the number of penetrations into pressure vessels..Only if a penetration will provide significant additional information and/or safety, should it be installed.
This is not the case with the inspection ports.
While inspection ports would allow i
direct inspection of the upper support plate, an equally adequate inspection for determination of the progression of the denting
o-p.
Mr. Harold R. Denton 3
Vinoix A Es.zcTunc Ano Powen COMPANY To phenomenon can be performed using the existing lower SG hand hole penetrations.
Additionally, eddy current probing effectively reveals the progress t f the denting process at everf support plate in the SG.
III. Propased Course of Action During the upcoming refueling outage, now scheduled for December,1980 -
January,1981, we propose to take the following actions pending.comple-tion of ongoing reviews of the corrosion abatement programs:
A.
Eddy Current Inspections We will perform eddy current tube inspections during the upcoming outage.
Based on the results of these inspections, we will be able to determine how effectively the corrosion has been controlled.
If a significant amount of corrosion continues to occur, installation of the inspection ports will be reconsidered.
B.
Hand Hole Inspection Additionally, we will perform an inspection of the lower support plate through the lower hand hole (s).
The observations of the extent of support plate corrosion will provide substantial and ade-quate evidence about the condition of the top support plate without t
the installation of the inspection port.
If the hand hole inspec-tion reveals substantial additional corrosion, a decision can be made at that time to re-evaluate the need for the inspection ports.
C.
Boric ' W Program Review and H M nitoring 2
The results of the hydrogen monitoring program are presently undergoing intensive review by Westinghouse.
It is too early to completely determine the adequacy of our corrective actions in stop-ping the corrosion.
We believe it is premature, in the absence of progressive accelerated support plate corrosion, to install inspec-tion ports at this time.
IV.
Conclusions In light of tire preceding discussion, we feel it is prudent to reconsider our earlier intention to install SG inspection ports at North Anna Unit 1 until after more inspections are performed.
No significant additional benefit from an operational or safety standpoint can be identified for installation of inspection ports.
Installation would result in addition-al personnel exposure (about 7.5 man-rem), another penetration into a critical pressure vessel with the attendant increased risk of a steam-break accident, substantial expenditures of manpower and monetary i
l resources, and impact and likely delay of the refueling outage which w ald incur additional expenses on our customers.
em tir. Harold R. Denton 4
Vs aoix A Etrcinic Am Powra CourAvr To We agree that, in the presence of severe denting, inspection ports are a valuable inspection tool.
We wish to, at a minimtu, quantify the efF.c tiveness of our corrective actions prior to any decision to install them.
This can most effectively be donc during the upcoming outage using eddy current and hand hole inspections. A decision on the installatic,c of the inspection ports can justifiably be delayed until these results are known.
If you have any questions, or require addi' ional information, please contact this office.
Very truly yours,
@B.R.SylviaM C
llanager - Nuclear Operations and Flaintenance cc: Fir. James P. O'Reilly www Ny-we.
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