ML18153B644
| ML18153B644 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna, 05000000 |
| Issue date: | 03/15/1989 |
| From: | Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 88-433A, IEB-88-008, IEB-88-8, NUDOCS 8903220353 | |
| Download: ML18153B644 (6) | |
Text
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e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 W. R. CARTWRIGHT VICB PBBSIDBNT NUCLBAB March 15, 1989 United States Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D. C.
20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 NORTH ANNA POWER STATION UNITS 1 AND 2 SUPPLEMENTAL RESPONSE TO NRC BULLETIN NO. 88-08 Serial No.
88-433A NO/AVB/RPC:vlh RS Docket Nos.
50-280 50-281 50-338 50-339 License Nos. DPR-32 DPR-37 NPF-4 NPF-7 THERMAL STRESSES IN PIPING CONNECTED TO REACTOR COOLANT SYSTEM By letter (Serial No.88-433) of October 3, 1988, Virginia Electric and Power Company identified several unisolable sections of piping which are potentially susceptible to the thermal stress concern addressed by NRC Bulletin 88-08.
In that letter, we committed to perform nondestructive examinations (NOE) and establish a program to monitor pipe temperatures in selected lines which could be subjected to high cycle fatigue. Temperature monitoring is considered to be an interim solution. Correspondingly, we committed to address long-term solutions for this issue by March 15, 1989.
This letter provides a status of nondestructive examination results obtained to date and provides our intended course of action to meet the requirement for long-term continuing assurance that this piping will not be subject to fatigue failure.
Nondestructive examination of the lines susceptible to high cycle fatigue has been completed for Surry Power Station Units 1 and
- 2.
The test results provided no indication of adverse effects due to thermal stratification.
As required by NRC Bulletin 88-08, NOE results for North Anna Power Station will be submitted thirty days following the completion of the 1989 refueling outages. provides a summary of our study regarding long-term solutions to resolve this issue. It is our intention to continue the ongoing evaluation to determine a long-term solution as supplemented by temperature data collection during one operating fuel cycle for Surry Units 1 and 2 and North Anna 1 and
- 2.
Also proVided are the status and current results of our NOE effort.
Should an indication of thermal stratification arise at either station during the next operating cycle, the data will be evaluated to determine the appropriate course of action.
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The information provided in this response is true and accurate to the best of my knowledge.
Attachment cc:
United States Nuclear Regulatory Commission Region II 101 Marietta Street, N. W.
Suite 290()
Atlanta, Georgia 30323 Mr. J. L. Caldwell NRC Senior Resident Inspector North Anna Power Station Mr. W. E. Holland NRC Senior Resident Inspector Surry Power Station
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e COMMONWEALTH OF VIRGINIA)
)
COUNTY OF HENRICO
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e The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by W.
R. Cartwright who is Vice President -
Nuclear, of Virginia Electric and Power Company.
He is duly authorized to execute and file the foregoing document in beha 1f of that Company, and the statements in the document are true to t,he best of his knowledge and belief.
Acknowledged before me this _l.S.._ day of ~
, 19 89.
My Commission expires: ~d,,,,,~ ft
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Notary Public (SEAL)
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NRCB-88-08 LONG-TERM SOLUTION EVALUATION THERMAL STRESSES IN PIPING CONNECTED TO RCS NRC Bulletin 88-08 describes the potential for Reactor Coolant Loop (RCL) branch lines to experience thermal oscillations and stratification that could lead to high cycle fatigue cracking due to valve leakage.
Six Safety Injection lines on each unit at North Anna and Surry have been identified as potentially affected by the concern. Each of the potentially affected lines are to be non-destructively examined (NOE) and instrumented with thermocouples at preselected locations to detect thermal stratification.
The number of thermocouples and NOE locations is shown in Table 1.
NOE *locations were chosen at each elbow between the RCL and the first check valve on branch lines potentially affected by thermal stratification.
The elbow constitutes an area of discontinuity where stresses usually intensify, and is therefore, an area of high stress location. NOE of a circumferential slice through the middle section of selected elbows was chosen since one of the cracks at the Tihange plant initiated alon~ the side of an elbow (reference: Supplement 1 to NRC Bulletin 88-08). NOE of the base metal at either side of each elbow weld was included as part of the NOE at the weld location.
The locations chosen for thermocouple installation were based on the lengths of the potentially affected segments and consideration of thermal attenuation zones.
The temperature of non-flowing RCL branch piping is a function of its proximity to the-branch _intersection. The fluid closer to the branch point will be more influenced by the pipe run fluid temperature., and the effect of the RCL fluid temperature will be attenuated by distance.
The.following alternatives have been investigated for North Anna and Surry as potential long-term measures to ensure that the unisolable branches to the RCL are not subject to fatigue cracking:
- a.
Develop a program for valve leak testing and for NOE during outages.
This involves additional leak testing provisions, instituting augmented leak testing, inspection, and NOE; and taking corrective maintenance and repair actions on affected valves.
- b.
Install a permanent temperature monitoring system, with temperature indication provided in the Control Room. Evaluation criteria based on leakage rate, frequency of oscillations and augmented NOE would become part of a permanent surveillance program.
- c.
Install a heat tracing system to maintain water at a uniform temperature through the potentially affected unisolable pipe cross-section.
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- d.
Alter valve line-ups and/or install additional manual
- or motor-operated valves (with redundant power source) in series with existing valves along each potential leak path to provide double isolation and eliminate the potential for leakage significant enough to be a thermal stratification concern.
- e.
Develop a piping system whose function would be to bleed off fluid immediately downstream of any normally closed single isolation valves which separate the high pressure charging fluid from the RCS.
- f.
Relocate the first check valve on unisolable branches to the RCL to within a distance of four pipe diameters.
Alternatives a. and d. are being actively pursued.
Our approach is to monitor thermal stratification with the temporary thermocouples that have been installed at Surry and that will be install.ed at North Anna until useful data is obtained and evaluated.
Based on the ultrasonic examinations at Surry and those examinations to be performed at North Anna, we believe that the additional time spent in recording and evaluating temperature data will enhance the effort to pursue the appropriate long-term solution.
'l-TABLE 1 LINES POTENTIALLY AFFECTED BY THERMAL STRATIFICATION NO. OF NOE NOE LINE NO.
DESCRIPTION NO.OF TIC'S LOCATIONS STATUS NORTH ANNA UNIT 1##
6"-RC-16 SI to Hot Leg A 2
3 In Progress 6"-RC-17 SI to Cold Leg A 8
6 In Progress 6"-RC-18 SI to Hot Leg B 2
3 In Progress 6"-RC-19 SI to Cold Leg B 2
2 In Progress 6"-RC-20 SI to Cold Leg C 2
3 In Progress 6"-RC-21 SI to Hot Leg C 8
9 In Progress NORTH ANNA UNIT 2##
6"-RC-416 SI to Hot Leg A 2
3 In Progress 6"-RC-417 SI to Cold Leg A 2
3 In Progress 6"-RC-418 SI to Hot Leg B 2
3 In Progress 6"-RC-419 SI to Cold Leg B 2
2 In Progress 6"-RC-420 SI to Cold Leg C 2
3 In Progress 6"-RC-421 SI to Hot Leg C 7
3 In Progress SURRY UNIT 1 6"-RC-16 SI to Hot Leg A 2
2 Complete*
6"-RC-17 SI to Cold Leg A 8
2 Complete*
6"-RC-18 SI to Hot Leg B 2
2 Complete*
6"-RC-19 SI to Cold Leg B 0#
2 Complete*
6"-RC-20 SI to Cold Leg C 2
2 Complete*
6"-RC-21 SI to Hot Leg C 7
2 Complete*
SURRY UNIT 2 6"-RC-316 SI to Hot Leg A 2
3 Complete*
6"-RC-317 SI to Cold Leg A 0#
2 Complete*
6"-RC-318 SI to Hot Leg B 7
3 Complete*
6"-RC-319 SI to Cold Leg B 4
2 Complete*
6"-RC-320 SI to Cold Leg C 0#
3 Complete*
6"-RC-321 SI to Hot Leg C 2
. 2 Complete*
- NOE has been completed.
No indications were found.
- These lines in Thermal Attenuation Zone 1 (thermal mixing) have similar geometries to lines which are instrumented and T/C's were not installed due to ALARA considerations.
- Number of planned T/C locations.