ML20195E519
| ML20195E519 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/01/1988 |
| From: | Goldberg J HOUSTON LIGHTING & POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-88-009, IEB-88-9, NUDOCS 8811080160 | |
| Download: ML20195E519 (11) | |
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'The Light company P.O. Box 1700 liouston, Texas 77001 (713) 228 9211 Ilouston Lighting & Power.
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November 1, 1988 ST-HL-AE-2832 File No.:G3.3 10CFR50 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Units 1 & 2 Docket No. STN 50-498/499 Response to NRC Bulletin 88-009:
"Thimble Tube Thinning in Westinghouse Reactors" Houston Lighting & Power Company (HL&P) has evaluated the subject bulletin received on August 5, 1988, and submits the attached response for Units 1 & 2 of the South Texas Project Electric Generating Station. Also included in this response is a summary of the results of the inspection performed on the Unit I thimble tubes in September 1988.
Based on this data, IIL&P plans to conduct the next inspection after an additional 21 weeks of three or four Reactor Coolant Pump operation.
Assuming continuous Unit 1 operation, the next inspection would begin in February 1989.
This interval is technically justified in the attachments to this letter.
HL&P is available for a conference with you at your convenience to discuss this interval.
If you should have any questions on this matter, please contact Mr. H. A. McBurnett at (512) 972-8530.
b J. H. Goldberg Group Vice President, Nuclear JHG/WPE/n1 Attachments:
- 1) Response to NRC Bulletin 88-009.
- 2) Rasults of Thimble Tube Inspections Performed in September, 1988.
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NL.88.180.01 8G11080160 G81101 PDR ADOCK 05000490 PDC
,11 >uston 1.ighting & Power unnpany ST-HL-AE-2832 Fila No.: G3.3 Page 2 CCt.
Reglenal Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission' Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company i
Arlington, TX 76011 P. O. Box 1700 Houston, TX 77001 George Dick, Project Manager U. S. Nuclear Regulatory Commission INPO
' Washington, DC 20555 Records Center 1100 circle 75 Parkway Jack E. Bass Atlanta, Ga. 30339-3064 Senior Resident Inspector / Operations e/o U. S. Nuclear Regulatory Commission Dr. Joseph M. Hendrie P. O. Box 910 50 Be11 port Lane Bay City, TX 77414 Be11 port, NY 11713 J.
I. Tapia Senior Resident Inspector / Construction c/o U. S. Nuclear Regulatory Commission P. O. Box 910 Bay City, TX 77414 J. R. Newman, Esquire Newman & Holtzinger, P.C.
I 1615 L Street, N.W.
Washington, DC 20036 R. L. Range /R. P. Verret Central Power & Light Company P. O. cox 2121 Corpus Christi, TX 78403 l
R. John Miner (2 copies) j Chief Operating Officer City of Austin Electric Utility 721 Barton Springs Road Austin, TX 78704 l
R. J. Costello/M. T. Hardt i
City Public Service Board l
l P. O. Box 1771 San Antonio, TX 78296 l
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Revised 08/24/88 i
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter
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Houston Lighting & Tower
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Docket Nos. 50-498 Company, et al.,
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50-499
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South Texas Project
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Units 1 and 2
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AFFIDAVIT J. H. Goldberg being duly sworn, hereby deposes and says that he is Group Vice President, Nuclear of Houston Lighting & Power Company; that he is duly authorized to sign and file with the Nuclear Regulatory Commission the attached response to NRC Bulletin 88-009: is familiar with tha content thereof: and that the matters set forth therein are true and correct to the best of his knowledge and belief.
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(J. H. Goldberg
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Group Vice president, Nuclear Subscribed ajd sworn t a Notary Public in and for The State of Texas this j day of h,o before me, r, _, 1988.
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D tutKLL ~ k0dh Notarf Public in arid for the
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ST-HL-AE-2832 n
. File No.: G3.3 Page 1 of 3 s
NRC Bulletin 88-009 "Thimble Tube Thinnina In-Westinghouse Reactors" t
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' Action Item i
'Each addressee is requested to establish an inspection program to monitor thimble tubo performance.. This inspection program should includes o
the establishment,. with technical justification, of an appropriate thimble tube wear acceptance criterion (for example, percent through-wall loss). This acceptance criterion should include allowances for such items as inspection methodology and wear scar geometry uncertainties.
o the establishment, with technical justification, of an appropriate inspection frequency (for example, every refueling outage).
o the establishment of an inspection methodology that is capable of adequately detecting wear of the thimble tubes (such as addy current testing).
Response
Bottom Mounted Instrumentation (BMI) thimble tube wear at South Texas Project Electric Generating Station (STPEGS) Unit 1 and Unit 2 has been discussed in the past with the NRC by HL&P and Westinghouse. This wear has been the subject of several letters (see the list of references below for the recent correspondence).
The STPEGS reactor cores are of a fourteen foot design like that in use in several European plants.
Prior to initial operation of the STPEGS, accelerated thimble tube wear was identified at the European plants. To correct this problem, a flow limiter was dusigned and installed on these plants as well as STPEGS Unit 1.
Unit 1 went into initial operation with the flow limiter installed.
Immediately prior to initial operation of Unit 1, one of the European utilities using flow limiters discovered that the accelerated wear problem had not been corrected by the flow limiters. As a result of these events, Westinghouse implemented an inspection plan for the BMI thimble tubes.
NL.88.180.01
.r ST-HL-AE-2832 File No.: G3.3 Page 2 of 3 The first inspection was conducted after approximately four (4) weeks of three or four Reactor Coolant Pump (3-4 RCP) operation (December 1987) and no thimble tube wear was identified.
An agreement with the NRC was reached to conduct another inspection after twelve weeks of 3-4 RCP operation (May 1988).
Wear was identified in this inspection and actions were taken to reposition and cap thimble tubes in accordance with the program plan described in the referenced correspondence.
Subsequently, HL&P agreed to conduct another inspection after sixteen weeks of 3-4 RCP operation (September 1988).
In the September 1988 inspection, HL&P identified wear similar to that identified in May 1988.
As described above and in the referenced letters, an inspection program has been implemented for Unit 1.
The program consists of a periodic eddy current inspection of the BMI thimble tubes following a specific period of 3-4 RCP operation.
For each inspection, the 58 BMI thimble tubes are examined using eddy current equipment.
The established eddy current technique and data analysis assumes a wear scar of 90 degrees and accounts for uncertainties in the wear pattern.
The results from this process are conservative.
Huasurement of the wear scar geometry by physical examination in a hot cell of thimble tube samples from Tihange Unit 3 in Belgium (Reference 5) has confirmed the conservatism of the eddy current technique.
The acceptance criteria is based on 60% thimble tube wall loss (Reference 2).
As stated in Reference 5, the thimble tubes can actually tolerate much greater than 60% wall loss. This amount of wall loss was chosen as a conservative value to use in determining which corrective action to take to preclude thimble tube leaks.
Based upon the results of the eddy current inspection, the decision was made for each thimble tube whether to leave the thimble tube as is, to reposition the thimble tube, or to reposition the thimble tube and remove it from service by capping. The inspection results were used to determine the unique wear rate for each individual thimble tube, assuming a linear wear rate.
This wear rate is based on the time of operation that the thimble tube has been subjected to wear at a specific location.
The derivation of this wear rate included an additional 10% wall loss as an extra measure of conservatism. The projected wear until the next inspection is calculated for each thimble tube using the calculated wear rate and the time to the next inspection.
Thimble tubes that have an actual wear of 60% or more are removed from service by capping after repositioning.
Thimble tubes projected to reach or exceed a total wear of 60% before the next inspection are repositioned to shift the worn location out of the wear area.
If, after repositioning, a thimble tube is projected to exceed 60% wear in its new location, then the thimble tube is also capped.
The remaining thimble tubes are left as they are, since they have a projected total wear of less than 60% at the next inspection with no action taken.
NL.88.180.01
Attechment i ST-HL-AE-2832 File No.: G3.3 Page 3 of 3 The long term corrective action for the problem of thimble tube wear is to remove the flow limiters and install stiffer thimble tubes which have a larger diameter and a thicker wall than the present thimble tubes.
The stiffer thimble tubes have been shown by test to have less tendency toward vibration and, therefore, much lower wear rates at the flow rates experienced in this region of the core. Additionally, STPEGS Unit I has added a manual isolation valve to each of the thimble tubes to isolate Reactor Coolant System leakage should wear-through occur.
These valves, as well as the stiffer thimbles.
will be installed in Unit 2 prior to initial operation. Magnetic ball check valves will be installed in the thia.ble tubes during the next Unit 1 inspection outage currently planned for late February 1989 (assuming continuous Unit 1 operation). These check valves will be installed in Unit 2 prior to initial operation.
The flow limiters will be removed and stiffer thimble tubes installed at the first Unit i refueling outage.
Future inspection intervals are being developed as follows.
The new Unit 2 thimble tubes will be inspected prior to the first refuel ng of Unit 1.
The purpose of thir inspection se,nedule is to provide information on the performance of the new stiffer thimble tubes prior to their installation in Unit 1.
As a minimum, the thimble tubes on each unit will be inspacted no later than the first refueling outage after installation of the new thimble tubes.
Subsequent inspection intervals will be established based on the results of wear rate calculations. The results of the Unit 1 eddy current 2
inspection performed in May 1988 were described in Reference 3 along with the corrective actions taken. The results of the Unit 1 inspection performed in September 1988 are described in Attachment 2 along with the correctiv6 actions taken.
1 References (Letters from HL&P to the NRC) i 1.
ST-HL-AE-2458 of January 5, 1988 2.
ST-HL-AE-2490 of February 3, 1988 3.
ST-HL-AE-2655 of May 12, 1988 4.
ST-HL-AE-2737 of July 18, 1988 5.
ST-HL-AE-2760 of August 9, 1988
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NL.88.180.01
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Attechment 2
' ST-HL-AE-2832 File No.:'G3.3 Page l.of 5 '
NRC Bulletin 88-009 "Thimble Tube Thinnina In Westinahouse Reactors" L
This attachment describes the results of the recent addy cu.-rent ~ inspection of the 58 BMI thimble tubes at STPEGS Unit 1 and the corrective actions taken.
These results and corrective actions were initially. discussed with the NRC by.
telephone'on Octcber 3, 1988.
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.The inspection and data analysis.was performed by Westinghouse personnel from September 25 to September 29, 1988 during an outage of Unit 1.-
The established oddy current: inspection technique and data analysis assumed a wear 1 car of 90 degrees. This yielded conservative reporting of the inspectio,n results. The eddy current technique.could not accurately. resolve wear that was less than 10 percent.
The results and actions taken are summarized as follows:
a.)
16 thimble tubes had no detectable wear and were left as is.
b.)
24 thimble tubes with wear were projected not to meet or exceed 60%
wear.before the next inspection and were left as is, c.)
14 thimble tubes with wear were projected to meet or exceed 60% wear in their current location and were repositioned.
d.)
I thimble tube with wear was expected to meet or exceed 60% wear at its current and repositioned locations and was repositioned and capped.
e.)
3 thimble tubes were repositioned and capped in May 1988 and were left as is after the September 1988 inspection.
Figure i shows the wear found for each thimble tube location in the core.
This wear is at the flow limiter area of the thimble and is expressed as percent wall loss. Also attached is Figure 2 which shows the wear found by the previous inspection in May 1988.
Some thimble tubes also had slight wear (10-25%) in areas other than at the flow limiter.
This slight wear was determined to be acceptable and no corrective actions were necessary.
The thimble tubes had been subjected to an additional 16 weeks of three or four Reactor Coolant Pump operation since the previous inspection in May 1988.
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ST-HL-AE-2832 File No.: G3.3 Page 2 of 5 During the Unit 1 outage, manual valves for thimble tube isolation were installed.
Each of the thimble tubes can now be isolated by manually closing the valve in case of a thimble tube leak.
It is planned to install magnetic ball check valves in series with the manual valves during the next Unit 1 inspection outage.
The magnetic ball check valve would serve as an automatic isalation valve since the ball would seat to stop the leakage flow upon being subjected to the primary system pressure.
Table i shows the corrective actions that were taken during the September 1988 outage. These actions were based on the projected wear expected until the next inspection as shown on the table. The projected wear included an added 10 percent margin.
The next inspection is planned after 21 additional weeks of three or four Reactor Coolant Pump operation. The earliest this would occur is late February 1989.
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e ST-HL-AE-2832 File No.: G3.3 Page 3 of 5 TABLE 1 THIMBLE TUBE CORRECTIVE ACTIONS Thimble Tube Projected Total Wear after 21 Number Action Taken more weeks with Action Taken L-13 CAP & REPOSITION N/A N-02 REPOSITION 55%
J-08 REPOSITION 51 H-15 REPOSITION 46 N-08 REPOSITION 46 3-03 REPOSITION 51 P-09 REPOSITION 50 R-11 REPOSITION 46 N-13 REPOSITION 45 H-11 REPOSITION 41 L-15 REPOSITION 34 P-04 REPOSITION 37 E-11 REPOSITION 49 D-12 REPOSITION 35 F-01 REPOSITION 35 Notes o Manual isolation valves were installed on til thimbles.
o Remaining thimbles were left as 1s.
NL.88.180.01
FIGURE I ATTACHMENT a 4 LOOP CORE CROSS SECTION Q%fogsaa PAGE 4 0F 5 E.C.T. RESULTS - SEPTEMBER 1988 270 A
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= THtMBLE TUBE LOCATION
- DICATT.S A TH!MBLE TUBE THAT WAS INDICATES THAT THE THlWBLE TUBE WAS REPOSm0NED AND IN NO NEW SCAR OCCURRED AT THE FLOW UMITER REGION REPOSm0NED AT LAST INSPECTION 1
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FIGURE 2 XITACHMENT 2 4 LOOP CORE CROSS SECTION
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PAGE 5 0F 5 E.C.T. RESUIHS - MAY 1988 270 A
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