ML20195E250
| ML20195E250 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 10/31/1988 |
| From: | Randazza J Maine Yankee |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-88-008, IEB-88-8, MN-88-101, NUDOCS 8811070316 | |
| Download: ML20195E250 (9) | |
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MaineYankee RELIABLE E'.ECTRICliv FOR lAirhE SEE 'C72 EDtSON DRIVE AUGUSTA, MAINE 04330.(207) 622 4868 October 31, 1988 HN-88-101 UNITED 3?MEs NUCLEAR REGULATOP.Y COMMISSION Attention:
Document Control Desk Hashington
- 3. C.
20555
References:
(a) License No. DPR-36 (Docket No. 50-309)
(b) NRC Bulletin 88-08:
Thermal Stresses in Piping Connected to Reactor Cooiant Systems, dated June 22, 1988
Subject:
Response to NRC Bulletin 88-08 Gentlemen:
The purpose of this letter is to provide a response to NRC concerns documented in NRC Bulletin 88-08, "Thermal Stresses in Piping Connected to Reactor Coolant Systems", which requests that utilities address the issue of thermal stresses in unisolable piping connected to the reactor coolant system (RCS). Maine Yankee's response is contained in Enclosure 1.
A review of systems connected to the RCS vas performed to determine whether unisolable sections of piping connected to the RCS can be subjected to struses from temperature stratification or temperature oscillations that could t.e induced by leaking valves and were not evaluated in the design analysis of the piping.
Based on the review and evaluation summarized in Enclosure '. there are no unisolable sections of pipin2 connected to the RCS that may hwe been subjected to excessive thermal stresses induced by leaking valves whkh have not been previously evaluated in the piping design analysis. So further actions are required by Bulletin 88-08.
L 8811070316 881031 1
PDR ADOCK 05000309
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MaineYankee United States Nuclear Regulatory Commission Page Two Attention:
Document Control Desk MN-88-101 Please contact us if you have any questions or require additional information.
Very truly yours, MAINE YANKEE M*hv l
John B. Randazzi President l
SOE:BJP Enclosure c: Mr. Richard H. Messman Mr. Milliam T. Russell Mr. Cornelius F. Holden Mr. Patrick M.
bears STATE OF MAINE Then personally appeared before me, John B. Randazza, who being duly sworn did state that he is President of Maine Yankee Atomic Power Company, that he is duly authorized to execute and file the foregoing response in the name and on behalf of Maine Yankee Atomic Power Company, and that the statements therein are true to the best of his knowledge and belief.
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b MaineYankee ENCLOSURE 1 MAINE YANKEE RESPONSE TO NRC BULLETIN 88-08 Bulletin Action 1:
l Review systems connected to the RCS to determine whether unisolable
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sections of piping connected to the RCS can be subjected to stresses from temperature stratification or temperature oscillations that could be induced by leaking valves and that were not evaluated in the design analysis of the piping. For those addressees who determine that there are no unisolable sections of piping that can be subjected to such stresses, no additional actions are requested except for the report required below.
Maine Yankee Responiti Systems Reviewed The RCS and connected systems wer6 reviewed to determine whether uninsolable sections of piping connected to the RCS are subjected to stresses from temperature stratification or oscillations that could be induced by leaking valves. As requested in the NRC bulletin, this review focused on operations where system pressure might potentially be higher than RCS pressure and where system temperature could potentially be cooler than RCS temperature. Such conditions could promote leakage of cool water into the RCS.
Table 1 lists the RCS penetrations that were evaluated for l
the concerns expressed in the Bulletin.
l The following systems connected to, or part of, the RCS were reviewed:
Reactor Coolant System Chemical and Volume Control System SafetyInjection Loop Drain Sample System Reactor Hater Level Indication System Reactor Vessel Gas Vent System The Loop Drain, Sample, Reactor Vessel Gas Vent and Reactor Water Level l
l Indication systems are no m ily valved out during power operation with no active components that would cause system pressure to increase above primary system pressure to promote valve leakage.
These systems, i
therefore, were excluded from the more detailed systems evaluation.
System Evalugtlon An evaluation of systems operations was perfonned on the remaining applicable systems where system pressure might potentially be higher than RCS pressure and system temperatures potentially cooler than RCS temperature.
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MaineYimkee Pressurizer Main Spray Lines:
The pressurizer main spray system acts to reduce pressurizer pressure by spraying cold leg water into the steam space.
The upper portion of the spray system consists of a horizontal section of piping leading to the pressurizer spray nozzle. During plant heatups and c %1 downs, when less than three Reactor Coolant Pumps are operating, l
the normal bypass spray flowrate may be insufficient to maintain this uppermost horizontal section of spray piping full of water.
During this potential low flow condition, pressurizer steam could fill the upper part of the spray piping with cooler water flowing in the lower half resulting in a diametrical temperature difference across the pipe.
Stratified flow conditions have been detected at some plants during plant heatups.
No known fatigue cracking, however, has been detected in the pressurizer spray piping.
In response to recommendations that i
resulted from an evaluation of stratified flow loading conditions through CEOG-Task 482, "Pressurizer Spray System Thermal Fatigue Evaluation," Maine Yankee inst,rumented the spray line header with thermocouples.
Thermal stri.tification was not observed during either
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heatup, cooldown or normal operating conditions.
Furthermore, sections of the spray line did not exhibit any evidence of fatigue cracking during the ISI program NDE examinations.
Thus, there is no evidence that the spray line was subjected to any unanalyzed thermal stresses due to leaking valves.
P Pressurizer Auxiliary Spray Lines:
i The auxiliary spmy system acts to reduce pressurizer pressure by t
providing diverteo charging flow to the steam space in the pressurizer.
The autiliary sprays are utilized when the main spray system is unavailable, typically when the RCPs are not operating.
i During normal plant operation, the auxilia,'y spray line is isolated from the charging system bj a single remotely operated valve.
Although the charging systeo typically operates around 400*F, during i
transient conditions the temperature may drop as low as 120*F. The auxiliary spray line is a two int.5, schedule 160 pipe.
The auxiliary spray line taps into the main spray system well below the water line i
in the main spray line.
These lines would, therefore, always be filled with water.
The amount of leakage required to promote stratified flow (<.2 gpm) would not contain sufficient energy to provide stratified cooling.
The relatively small pipe has a higher probability of mixing (compared to a large diameter pipe) since the l
threshold for transition to turbulent flow is a function of pipe diameter (among other parameters). Also, the relatively thick pipe walls (compared to pipe diameter) enhance conduction around the circumference of the pipe which tends to equalize pipe wall temperatures.
Further, sections of the auxiliary spray line at M11ne L
Yankee did not exhibit any evidence of fatigue cracking during the L
l ISI program NDE examinations.
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MaineYankee Hot Leg Injection Lines:
The hot leg injection lines are separated from the charging pumps by multiple isolation valves. Due to the number of isolation valves in these lines, leakage would not be expected to occur.
In addition, the relatively thick pipe walls (compared to pipe diameter) would promote heat conduction around the circumference of the pipe and tend to equalize any uneven temperatures.
The smaller pipe has a higher probability of mixing because ths threshold after transition to turbulent flow is, in part, a function of pipe diameter.
f Safety Injection Lines:
Th6 safety injection headers are isolated from the high pressure CVCS by two isolation valves. Due to the multiple isolation valves'in the lines, leakage would not be expected to occur.
Furthermore, the high pressure safety injection header pressura is measured and the information is displayed on the main control board. Operators can l
monitor the header pressure to ensure that it remains lower than RCS l
pressure during normal operations.
Procedures will be revised to require HPSI header pressure to be logged and action levels for header pressure established.
Chemical and Volume Control System j
During normal operation the charging line passes full flow.
During charging isolation conditions, the CVCS is isolated from the RCS charging penetration by multiple valves which significantly reduce the probability of leakage into the RCS.
The charging line is a s
three inch schedule 160 pipe (2.6 inch ID).
The piping is vertical where it connects to RCS thereby providing good mixing and a low probability of thermal stratification.
The relatively small diameter j
and thick walls promote heat conduction around the circumference of the pipe which tends to reduce thermal bending stresses.
This pipe is also more flexible and, therefore, wre forgiving of such stresses than a larger line.
In addition, the amount of flow (even potential
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flow due to valve leakage) required to produce sufficient mixing to negate stratified conditions b very small for a pipe this size.
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MaineYankee Bullatin Action 2:
For any unisolable sections of piping connected to the RCS that may have been subjected to excessive thermal stresses, examine nondestructively the welds, heat-affected zones and high stress locations, including geometric discontinuities, in the piping to provide assurance that there are no existing flaws.
Maine Yankee Responsn Maine Yankee has determined that, based on the foregoing evaluation, there are no unisolable sections of piping connected to the RCS that may have been subjected to excessive stresses from temperature oscillations or thermal stratification that could be induced by leaking valves and which have not been previously evaluated in the design analysis of the piping.
Therefore, no further action is necessary.
Bulletin Action 3:
Plan and implement a program to provide continuing assurance that unisolable se:tions of all piping connected to the RCS will not be subjected to combined cyclic and static thermal and other stresses that could cause fatigue failure during the remaining life of the unit.
This assurance may be provided by (1) redesigning and modifying these sections of piping to withstand combined stresses caused by various loads including temporal and spatial distributions of temperature resulting from leakage across valve seats, (2) instrumenting this piping to detect adverse f
l temperature distributions and establishing appropriate limits on temperature distributions, or (3) providing means for ensuring that i
pressure upstream from block valves which might leak is monitored and does i
not exceed RCS pressure.
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Maine Yankee Responie-l This item is not applicab h to Maine Yankee.
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Dulletin Action 4:
for operating plants not in extended outages Action 1 should be completed within 60 days of receipt of this bulletin, and Actions 2 and 3. if required, should be completed befor the end of the next refueling outage.
If tha next refueling outage ends within 90 days after receipt of this
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bulletin, then Actions 2 and 3 may be completed before the end of the following refueling outage.
Balne Yankee Re.5RQaih Action 1 has been completed and is documented herein.
Actions 2 and 3 are l
not applicable.
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MaineYankee Table 1.
RCS Penetrations Evaluated for NRC Bulletin 88-08 1,INE NUMBER / VALVE NUMBER DESCRIPTION NOTES 2502-12" Surge Line 4
1504-3"/RC-17,27.37 Loop 1,2,3 overpressure isolation viv 7,8,12 1504-3"/RC-S-18,28,38 Loop 1,2,3, loop relief 1
1504-3/4"/RC-S-19,29,39 Loop 1,2,3 Th stop bonnet relief 12 1504-2"/RC-N-15,25,35 Loop 1,2,3 fill stop valve 2.5,8,9 2502-8"/RC-N-13.23,33 Loop 1,2,3 bypass stop valve 5,12 1*04-14" Loop 1,2,3 SI 2,3 1504-3/4"/RC-M-11,21,31 Loop 1,2,3 Th stop valve 7,8,12 1504-3/4"/RC-114,116.118,120 Loop 1 S/G high side dp isol. valve 6,8,10 RC-224,226,228,230 Loop 2 S/G high side dp isol. valve 6,8,10 RC-334,336,338,340 Loop 3 S/G high side dp isol. valve 6,8,10 1504-3/4"/RC-115.117.119,121 Loop 1 S/G low side dp isoi. valve 6,8,10 RC-225,227,229,231 Loop 2 S/G low side dp isol. valve 6,8,10 RC-335,337,339,3
Loop 3 S/G lot side dp isol. v41ve 6,8,10 1504-2"/RC-16.26,36 Loop 1,2,3 manual drain stop 1
1604-3/4"/RC-M-12.22,32 Loop 1,2,3 Tc stop valve 7,8,12 1504-2-1/2"/LD-1 Loop 1 to letdown 1
1504-1"/PR-9 Refueling level instrument tap 1
1604-3/4"/RC-S-110.220,330 Loop 1,2,3 Tc stop bonnet relief 7,8,12 1504-12" Residual Heat Removal (Loop 2)
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1504-2"/RC-N-14,24,34 Loop 1,2,3 Drain stop 1
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1504-3"/CH-46,5)
Loop 2,3 Charging Line Stop 5,7,8,10,11 1504-3/4" Containment Sump 1
1504-3"/PR-3,4 Pzr. spray valve inlet isolation 13 1504-3/4"/PP.-5,6 Pzr. spray valve bypass 13 1504-4" Spray header to Pzt.
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(Continued)
LINE NUMBER DfSCRIPTION NOTES 1504-2" Aux. Spray connection 7,8,9,10 N
1504-1"/PR-27.26,28, Pzt. instrumentation isol. valve 7.10,12 23,25,24 1503-3"/PR-S-11,12.13 Pzr. code safety 5,6 i
301-10" PSV/PORV header to quench tank 1
1504-3/4"/PR-18 Pzt. code safety sample 1
1504-3"/FA-N-16,17 PORY isolation 1
1504-2-1/2"/PR-S-14,15 PORV 1
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1 MaineYankee Table 1.
(Continued)
A J HDIES:
1 System pressure less than RCS pressure.
2 Multiple isolation valves between high pressure source and RCS.
3 Header pressure monitored and maintained at less than RCS pressure.
4 No isolation valve in piping to RCS.
S Geoeltry of piping is vertical or near vertical where piping connects to FCS thereby providing good mixing and low probability of thermal stratification.
6 No source of pressure to produce flow through leaking valves.
7 Small diameter pipe which does not support phenomenon of flow stratification - higher probability of mixing, even at low flow rates.
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Small diameter schedule 160 pipe; relatively thick pipe walls compared to pipe diameter which enhances conduction around the circumference of the pipe and tends to equalize pipe wall temperatures.
9 Section of pipe has previously been NDE'd via the ISI program - no indications of crackliig evident.
10 Small diameter piping which is more flexible and hence more forgiving af thermal bending stresses.
i 11 Injection rate to RCS when system is normally operating is sufficient to provide good mixing of liquid negating stratified conditions.
12 System pressure same as RCS pressure.
13 Temperature monitoriig of piping system indicates no stratification during heat-up, cooldown, or normal operat*on of the plant. 1 1
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