ML20155F574
| ML20155F574 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 10/04/1988 |
| From: | Cockfield D PORTLAND GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-88-008, IEB-88-8, NUDOCS 8810130306 | |
| Download: ML20155F574 (10) | |
Text
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memes WW David W. Cockfie!d Vice President, Nuc! car October 4, 1988 Trojan Nuclear plant Docket 50-344 License NPF-1 i
U. S. Nuclear Regulatory Commission ATTN!
Document Control Desk Washington DC 20555 l
Dear Sir i
Nuclear Regulatory Comm19sion (HRC)Bulletin 88-08, Supplements 1 and 2. "Thermal Stresses in pipinr. Connected to Reactor Coolant Systems" NRC Bulletin 88-08 requested that operating nuclear plant licensees review systems connected to the Reactor Coolant System (RCS) to determine whether 4
unisolable sections of piping connected to the RCS can be subjected to l
stresses from temperature stratification or temperature oscillations, i
Also, licensees were requested to nondestructively examine unisolable l
sections of piping connected to the RCS that may have been subjected to excessive thermal stresses.
They were also requested to implement a l
procram to assure that such piping will not be subjected to combined eyelic and static thermal and other stresses that could cause fatigue failure over l
the remaining life of the plant.
I Supplement 1 to the NRC Bulletin reported an event at the Tihange Nuclear plant in Belgium that appeared to be similar to the pipe crack at Farley i
Unit 2 which pronpted the bulletin. Supplement 2 emphasized the need for using enhanced ultrasonic testing and the use of experienced personnel to f
detect cracks in stainless steel piping.
i 4
portland General Electric Company (pCE) has completed the requested review I
of piping systems at the Trojan Nuclear plant.
Review results are 4
presented in the attachrent, i
I
$%h *lSS$ SS8
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'l PottkwlGeneral Bechic Comparv l
i Document Control Desk l
October 4, 1988 Pare 2
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I This report does not discuss thermal stratification of the pressurizar I
surge line. A summary report and data transmittal for the surge line wns previour'y submitted with our letter of September 27, 1988 (D. W. Cochfield l
to Document Control Desk).
,1 Sincerely, s
1 P
I l
l Attachment i
c:
Mr. John B. Martin l
Regional Administrator, Region V 4
U.S. Nuclear Regulatory Commission
}
j Mr. William T. Dixon
]
State of Oregon j
Department of Energy Mr. R. C. Barr l
j NRC Resident Inspector i
Trojan Nuclear plant I
l Mr. Biff Bradley Nuclear Management and 3
Resources Council Washington DC l
Subscribed and sworn to before me on this 4th day of October 1988.
l tl( +b f W Notary Public of Oregon I
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My Commission Expires:
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Trojan Nuc1ccr Plcnt Document Control D:ck Docket 50-344 Attachment License NPF-1 Page 1 of 8 Portland Ceneral Electric (PCE)
Response to NRC Bulletin 88-08; Thermal Stresses in Piping Connected To Reactor _ Coolant Systems i
Requested _ Action 1 Review systems connected to the RCS to detemine whether unisolable sections of piping connected to the RCS can be subjected to stresses from terrporature stratification or temperature oscillations that could be induced by leaking valves and that were not evaluated in the design analysis of the piping, l
PCE Response The following piping lines have been identified as having a potential for ex1periencing temperature ctratification or oscillation 7
i I
a.
The four high-pressure safety injection (SI) system lines to each RCS cold les from the boron injection tank (BIT).
b.
The Chemical ar.d Volume Control System (CVCS) normal and alternate
[
]
charging lines.
]
c.
The CVCS pressuriser auxiliary spray line.
l The four RCS high-pressure SI system piping connections have a potential for j
themal cycling. Two isolation valves in the 3-inch-diameter SI piping header (MO 8001A s d B) and a 1-inch BIT bypass isolation valve (8925) are l
l subjected to centrifugal charging pump (CCP)/RCS pressure differential across them. This differential pressure enn be approximately 350 pounds per square iner (psi) during nomal Plant operation.
Downstream of the isola-Lion valves, the 3-inch-diarneter SI piping header enters Containment j
(through containment Penetration P-44) and branches into four separate 1-1/2-inch SI lines, one line directed to each of the four RCS cold legs, i
j The horizontal sections of each piping spool between the first check valve cnd the cold les piping could potentially be subjected to thermal :yeling if there is leakage through the above-mentioned isolation valves, j
1 l
l Trojan's 3-inch normal and siternate charging lines were identifled as I
having a low probability of developing significant themal cycling.
The i
3-inch 1 solation valvc (CV-8146) in the nomal charging line and the 3-inch
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isolation valve (CV-8147) in the alternate charging line experience a stuill l
differential pressure across them dt ring nomal operation (estimated at 5 l
to 9 psi). This contributes to a loe susceptibility for developing i
significant leakage. Additionally, the charging lines at this point have exited the regenerative heat exchanger and fluid temperature is approxi-I mately 500'F.
However, if there is leakage from the above-mentioned
)
isolation valves, at a low flow rate, the heat loss from the piping could
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cool the fluid before it reaches the RCS piping.
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Trojen Nucleer plant Document Control D3ck Dockat 50-344 Attachment License NPF-1 page 2 of 8 Trojan's 2-inch prescurizer auxiliary spray line from the outlet of the resonerative heat exchanger has a single air-operated isolation valve (CV 8147).
Downstream of this isolation valve is a normally stagnant line to a single horizontal check valve (8377).
Downstream of the check valve, the line runs vertically up to connect with a 4-inch pressurizer spray line. This connection is a 4-inch tee (horizontal) with a 2-inch (vertical) branch.
This location is a "cold trap" that is not predicted to experience thermal cycling immediately downstream of the check valve (8377); however, there may be a potential for thermal cycling at the 4-inch tee in the event of iso 1 ration valve leakage.
Ecoues_ted Action 2 For any unisolabit sections of piping connected to the RCS that may have been subjected to excessive thermal stresses, examins nondestructively the welds, heat-affe:ted zones and high stress locations, including geometric disccatinuities, in that piping to provide assurance that there are no existing flaws.
PCE Response Based upon the results of the system review conducted, pCE performed nondestructive examination of the SI lir.es and normal and alternate charging lines. This is not intended to oe a final response to the requested action, rather a report of investigatior.s completed at this time.
Critical inspection locations for SI lines were identified as those points in the line most susceptible to thermal cycling (refer to attached Figures 1-4).
These critical inspection points are located between the horizontal check Valves 8900A-D and the RCS piping.
Radiographic (RT) examination has been l
performed at these locations.
The RT procedures / methods were evaluated to j
ensure they provided the best sensitivity for insido diameter pipe cracking i
and were adequate for observing radial cracks propagating f rom the pipe internal diameter. Because the locations identified were socket welds, a calibration block was used to establish the ability to detect defects at the identified locations with RT methods, i
The SI piping lines at these critical locations are 1-1/2-inch, Schedule 160, stair..ess steel, A376 Tp304 or 316. The piping design uses bent piping spools (five diameter radius bends) and American National Standards Institute (ANSI) 6000 class socket weld fittings.
Based on review of the RT films, PCE concludes that no defects are present in the SI lines at the critical locations.
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4 Trojen Nuclocr plant Docum:nt Control D3sk Docket 50-344 Attachment License NPF-1 page 3 of 8 The normal and alternate charging lines were already scheduled to undergo 4
nondestructive examination due to the unrelated pipe whip restraint contact j
issue described in our letter (u. W. Cockfield to USNRC Document Control Desk) of May 31, 1988. The method of testing the normal and alternate l
charging lines was ultrasonic inspection.
Locations for the ultrasonic inspections are shown in Figures 5 and 6.
These inspections were deemed i
j suf ficient to detemine if pipe cracks exist on the normal and alternate charging lines due to thermal cycling from leaking isolation valvas.
The results of these inspections reveal no cracks present in the normal and alternate charging lines at the points inspected.
l
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i Inspection locations are currently being identified for the pressurizer I
auxiliary spray line. Nondestructive examination at these locations will be performed during the next refueling outago and the results will be reported within 30 days of completion in accordance with the schedule requirements of i
i i
Fequested Action 3 I
plan and implement a program to provido continuing assurance that unisolable
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sections of all piping connected to the RCS will not be subjected to combined cyclic and statir 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 conbined stresses caused by various loads including temporsi and a
J spatial distributions of temperature resulting from leakage across valve
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seats. (2) instrumenting this piping to detect adverse temperature j
distributions and establishing appropriate limits on temperature d
distributions, or (3) providing means for ensuring that pressure upstream
[
]
from block valves which might leak is monitored and does not exceed N;S j
pressure.
l 4
1 pCE Response, PCE activities to this point have identified the piping lines which may have the potential for themal stratification or cycling.
By identifying l
critical piping temperature locations on these lines, placing temporary
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themal monitors 6t the critical locations, and monitoring these locations l
throughout st9tt-up into nomal power operations, pCE has sought to detemine if leakage is actually taking place and if this is causing themal
[
I stratification or eyeling at Trojan.
The placement of the monitors on the SI lines was planned such that two 3
l mechanisms of themal cycling could be observed. The first mechanism (at i
lower leakage rates) would result from the pipe being partit11y filled with l
cold water causing a temperature dif ference ( AT) from the bottom to the j
top of the pipe.
The second.hermal cycling mechanism (at higher leakage d
rates) could result f rom the SI pipe being ermpletely filled with colder l
water. The themal monitor readings would be compared against ECS cold les temperature in this case.
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Trojen Nucioce T1cnt Docum:r.t Control Dask Docket 50-344 Attachment License NPF-1 Page 4 of 8
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The placement of the monitors on the bottom of the charging lines was planned to address the detection of leakage. One sensor on oach line would not provido suf ficient data to investigato the thermal cycling effects, however, it would determine if any leakage was occurring.
Data points were recorded from the thermal monitors once overy 3 minutes i
during heatup from the normal refueling outage to Plant Mode 3 normal operating temperature. System parameters were monitored using existir.g i
Plant instrumentation with data points printed out once every minuto, i
This data has been transmitted to PCE's Nuclear Steam Supply System
)
(NSSS) vendor for formal evaluation.
Preliminary results indicate that i
2 leakago may be occurring; however, it has not resulted in thermal strati-l fication or cycling that would create an immediato concern.
Depending l
upon the final conclusions of this data review, PCE will evaluate what l
j further action may be required. PCE will complete the actions described in Action Paragraphs 2 and 3 of NRC Bulletin 88-08 before the end of the next refuelin6 sutage, and the results will be reported within 30 days of completion in accordance with the schedule requirements of the Bulletin.
If modifications to the Plant are required in response to Action 3 a separato schedule for these modifications will be provided at that time.
I ARA / deb i
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Docunant dontrol @oab EIE'EI CRITIC L
- NSPECi::ON LOCATY055"' '"'
HIGH PRESSURE 1%" SI' _::NES TO RCS REF: 7108-RC-250lR-3-60 i2" To 2e"_
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, Trojen Nuc1ccr Plant Docu ent Control Dask Attachesnt Pege 6 of C Docket 50-344 CRITICAL INSPECTION LOCATIONS
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ALTERNATE CHARGlNG LINE TO RCS REF: 7108-RC-250lR-6-1
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LEG LOOP A ULTRASONIC INSPECTION LOCATION
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Document Controi Des'k i
. Trojan Euclear Plant
.Dochet 50-344 Attachmsnt Page 7 of d
" " " " 8 "- 2 TEMPERATURE SENSOR LOCAT::ONS HIGF PRESSURE 1%" SI LINES TO RCS I
REF: 7108-RC'2501R 3-60 12" TO 28" 7%"
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l SYMBOL NOTES LOCATIONS FOR SURFACE I
MOUNTED TEMPERATURE SENSORS.
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SEE FIG. 8 FOR DETAILED TE LOCATION.
e Troicn Nuclear Plent Documsnt Control Dask i Docket 50-344 Attachment Page 8 of Q u e n e a r-i TEMPERATURE SENSOR LOCATIONS FIGURE 11 ALTERNATE CHARGING LINE TO RCS REF: 7108-RC-2501R-6-1 v 4' v11" 3" SCH.160 BUTT WELDS AgggaT' =4 N
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IGURE 11 NORMAL CHARGING L::NE "O RCS i
REF: 7108-RC-2501R-5-6 4
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REQUIRED FOR THIS LINE.
LOOP A SYMBOL NOTES LOCATIONS FOR SURFACE
, MOUNTED TEMPERATURE SENSORS.
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