ML20198D227
| ML20198D227 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 05/13/1992 |
| From: | Broughton T GENERAL PUBLIC UTILITIES CORP. |
| To: | |
| Shared Package | |
| ML20198D225 | List: |
| References | |
| NUDOCS 9205190227 | |
| Download: ML20198D227 (8) | |
Text
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METROPOLITAN EDISON COMPANY JERSEY CEfUU.L POWER & LIGliT COMPANY AND e
PENNSYLVANIA ELECTRIC COMPANY THREE MILE ISLAPD NUCLLitR STATION, UNIT 1 Operating License No. DPR-50 Docket No. 50-289 Technical Specification Change Request No. 214 This Technical Specification Change Request is submitted in support of Licensee's request to a change to Lperating License No. DPR-50 for Three Mile Island Nuclear Station, l!ait 1.
As a part of this request, proposed replacement page(s) are w:1uded.
GPU NUCLEAR CORPORATION BY:
M Vice President (Jnd Director, TMI-l Signed and sworn before ue this 13J,h day of May
, 1992.
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-1 UNITED S1ATES OF AMERICA NUCLEAR REGULATORY COMMISSION IN THE MATTER OF DOCKET NO S0-289 GPU NUCLEAR CORPORATION LICENSE NO. DPR-50 CERTIFICATE OF SERVICE This is to certify that a copy of Technical Specification Chage Request No.
214 of the Operating License for Three Mile Island Nuclear Lation Uni' 1, has, an the date given below been filed with executives of Londonderry Township.
Dauphin County, Pennsylvania; Dauphin County, Pennsylvania; and the Pennsylvania Department of Environmenta'. Resources, Bureau of Radiation Protection, by deposit in the United States mail, addressed as follows:
Mr. Jay H. Kopp, Chairman Mr. Russell L. Sheaffer, Chairman Board of Supervisors of Board of County Commissioners Londonderry Township of Dauphin County R. D. #1,-Geyers Church Road Dauphin County Cuurthouse Middletown, PA 17057 Harrisburg, PA 17120 Mr. William P. Dornsife, Acting Director Pennsylvania Dept. of Environmental Resources Bureau of Radiation Protection P.O. Box 2063
-Harrisburg, PA' 17120 GPU NUCLEAR CORPORATION BY:
bib VicePresidentjndDirector,TMl-1 DATE:
May 13, 1992 l
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I.
Technical Soccification Chance Reouest No. 214 GPU Nuclear requests that the following revision be made to the Facility Operating Licensa:
t Replace page 6.
II. Enson for__Chanae Based on gradually increasing OTSG 1eakage prior to the beginning of the 9R refueling outage, GPU Nuclear requested temporary authorization to increase the allowable primary-to-secondary (P/S) leakage rate above baseline from 0.1 to 0.2 gpm. The gradually increasing leakage trend wu believed to be caused by leaking plugs and/or joints, which did not reflect a potential vulnerability to tube rupture during normal operation or postulated accidents.
The NRC authorized (NRC letter dated 8/9/91 and attached SER - Amendment 163) the temporary increase in the allowable leakage rate based on information provided by GPU Nuclear.
During the 9R refueling outage, bubble and drip leakage identification tests confirmed leaking plugs to be the cause of the gradually increasing
?
leakage.
This TSCR requests a similar and permanent change to the license. The change would allow an increase to the allowable P/S leakage rate from 0.1 to 0.2 gpm, only when the increased leakage is judged to be caused by leaking plugs or joints, prior to shutting down and leak testing the facility.
Under all other conditions, such as rapidly increasing P/S leak rate events, the current 0.1 gpm limit would remain in effect.
The specific change to the Facility Operating License is as follows:
Paae 6 has been revised to reflect the permanent change in Section 2(c)(8)(2). The following statement reflects the change to the section:
"The leakage rate limit shall be 0.1 gpm a'ove the baseline leakage rate, unless the observed leakage is judged to be caused by f eaking plugs or joints, in which case the leakage rate limit may be increased to 0.2 gpm above caseline, and shall not exceed this limit from all sources.
If leakage exceeds the established leakage rate limit, the facility shall be shut down and leak tested."
The remainder of Section 2(c)(8)(2) is unchanged.
Additionally, reference to the temporary authorization to increase the allowable P/S leakage rate above baseline from 0.1 to 0.2 gpm, permitted by license Amendment 163, has been deleted.
III. Safety Evaluation -
The current Facility Operating License Section 2(c)(8)(2) states that if the P/S leakage rate exceeds the baseline leakage rate by more than 0.1 gpm, the facility shall be shutdown and leak tested.
If any increased leakage above baseline is due to defects in the tube free span, the leaking tube (s) shall be removed from service. The baseline leakage shall be re-established, provided that the Technical Specificatf n (TS) 3.1.6.3 is not exceeded. ~
TS 3.1.6.3 states that if the P/S leakage through the steam generator tubes exceeds one (1) gpm total for both steam generators, the reactor shall be placed in cold shutdown within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> of detection.
This proposed TSCR does not change the one (1) gpm limit imposed by TS 3.1.6.3.
Allowing GPU Nuclear the option to increase the allowable priraary-to-secondary leakage rate above baseline from 0.1 to 0.2 gpm under the condition cited herein does not pose a safety concern.
Leaking plugs or joints would be characterized by a slow evolution of P/S leakage rate.
Tho leak rate trend monitored during cycle 8 operation prior to the 9R refueling outage was typical of plug or joint leakage. Upon inspection of the OTSGs during the 9R outage, 25 explosive plugs and one (1)
Westinghouse rolled )1ug in the cold legs of both steam ger.erators were found to have been tie cause of the gradually increasing P/S leakage rate.
After the leaking plugs were repaired (during the 9R outage), the P/S leak rate was significantly reduced. Nevertheless, it is anticipated that some other plugs may develop similar leaks during future operating cycles.
The THI-l steam generators have approximately 3,300 >1ugs instc11ed, many of which are leak-limiting mechanical (rolled or ribaed) and explosive plugs. As such they are not a leak-tight design.
Cumulative leakage through some of th.se plugs is possible, due to the P/S pressure differences during plant ope'ation.
The steam generators were also previously repaired by kinetic expansion to repair tube defects within the upper tube sheet. The kinetic expansion joint is also a leak-limiting design and leakage through these joints is also possible.
The determination that the increasing leakage rate is caused by leaking plugs or jotrts will be based upon the behavior of the P/S leakage rate over time (i.e., a slow and somewhat predictable rate of change).
Data for this deter...ination will be obtained from plant off-gas grab samples which are used to determine the P/S leak rate.
The instantaneous leak rate change, if any, will be monitored by the main condenser off-gas radioactivity detector (RMA5). This instrument is a continuous monitor with alarms and would give the plant operators almost instantaneous indication of a tube leak or a dramatic change in the P/S leakage rate.
With respect to the behavior of leakage resulting from a single tube crack, previous analysis prepared by GPUN and reviewed by the NRC (see NUREG 1019, Supplement 1) reported on the stability of tube crack growth during normal operattag conditions, and during plant heat-up and cooldown cycles. Tube loading during start-up and cooldown is the only significant contributor to stable crack growth.
Thus, should a small P/S leakage result from a tube crack in an unnlugged tube, the existing crack, if growing at all, would-be growing very slowly due to the tube load during plant heat up and cooldown.
It would not propagate at normal operating conditions..
r The current 0.1 gpm license limit tsas imposed on THI-l specifically because of the occurrence of circumferential tube cracks initiating from the primary side (i.e., inner diameter of the tubes) during the early
'1980's. The sources of leakage during normal plant operation, however, may be a leaking plug (s), joint (s), or tube (s) individually or in combination.
Plug or joint leakage exceeding 0.1 gpm, esen if from multiple tubes, does not reflect a potential vulnerability to tube ruptures during normal operation or postulated accidents, j
During the past several years there have been many inservice inspections of OTSG tubes at THI-1. Thase inspections utilize the eddy current testing (ECT) technique. GPUN and the NRC review of the inservice inspection results indicates that the primary side circumferential cracks have not experienced significant growt1 in recent years.
Aho, the OTSGs are subjected to ECT during every refueling outage to ensure that their 1
integrity is acceptable, based on the population of tubes inspected, in accordance with the technical specifications.
If the P/S leak rate behavior warrants a leak test, bubble and/or drip tests would be performed to identify the leaking sources. Additionally, a cooldown leak rate evaluation prior to startup further demonstrates OTSG integrity.
- Thus, the existence of any leaking tubes is expected to have been identified prior to startup.
This TSCR proposes establishing an administrative leak rate limit of 0.2 gpm if the increased leakage is judged to be caused by leaking plugs or joints.
Distinguishing between plug, joint or tube leakage is based on the behavior of the observed leakage during normal operation.
Leakage through a small tube crack would be stable in nature, since a small crack would not be expected to grow (per the GPUN analysis and result of ECT referred to above) during normal plant operation.
The conditions under which tube leakage would change would be due to changes in tube loading during cooldown, start-up, or other transient conditions.
Plug or joint leakage, does not vary with OTSG tube loading conditions. Hence, a slow and somewhat predictable increase in the leak rate would indicate the increase is attributed to plugs or joints.
For a rapidly propagating circumferential crack, the. >wth during normal operation can be attributed to high cycle (high frequency, low stress) fatigue (HCF).
Peripheral or lane and wedge tubes, which art subject to very high cross flows and fluid velocities, are vulnerable to high cycle fatigue which could cause tube failure if a defeat were present. During i
March 1990, TMI-l experienced its first and only high cycle fatigue tube failure during normal operation shortly after restart from the Oycle 8 refueling outage.
During this experience then was a rapid increase in P/S _ leakage to indicate the rapid tube failure.
In this case, failure resulted in rapidly increasing leakage, but did not progress to duuble-ended tube _ rupture. An evaluation nf this incident showed that if a lane tube has a small defect it will propagate rapidly to a failure (NRC SER related to Amendment No.163).
This high cycle fatigue failure has typically occurred shortly after B&W (OTSGs) plants return to power following a refueling outage.
This confirms GPU Nuclear's previous analysis which indicated that cooldown tube loads could propagate a circumferential crack which will result in tube failure due to HCF during..-
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normal operation.
To reduce the potential for high cycle fatigue failure in tubes known to be at greatest risk to this phenomenon,125 of the lane wedge tubes in each OTSG, judged to have the highest potential for HCF failure, were sleeved.
HCF failure.
No sleeved tube in a B&W OTSG has ever suffered a The radiological effects due to a steam generator tube rupture have been evaluated in the TM1-1 FSAR, Section 14.1.2.10.
a double-ended ru)ture of one steam generator tube occurs withThe analysis assumes unrestricted disciarge from each end, and thus envelopes the change requested herein.
The TM'-1 iSAR Main Steam Line B' ak (MSLB) radiological consequences are based on a 1 gpm tube leak, and 1% failed fuel, which is extre:nely conservative considering past cycle fuel performance.
accident with a gross 0.2 gpm P/S leak rate is bounded.Thus, an MSLB Since the proposed 0.2 gpm leak rate limit is only a small fraction of that previously analyzed in the TMl-1 FSAR and the Technical Specification limit of the specific activity of the secondary system will not be changed, the environmental dose contribution from the initial leakage of 0.2 gpm would be a very small fraction of 10 CFR 100 limits.
The THI-1 Technical Specification (3.1.6.3) limit of I gpm to baseline, was intended to ensure that the off-site doses from an MSLB accident would be a small fraction of 10 CFR Part 100 limits.
wW not modify the Technical Specification limits.
This change Operation of the plant with an increased leak rate limit of 0.2 gpm above baseline when the increased leakage rate is judged to be caused by leaking plugs or joints does not present any significant increase in off-site radiological consequences and would remain within a small fraction of 10 CFR Part 20 limits.
due to the P/S leakage increase (i.e., leakage of boric acid i secondary side may affect the pH), pH will be maintained to within the secondary chemistry specification With pH maintained within specification, there are no unexpe.cted erosion / corrosion concerns in the secondary system.
outage revealed that tiie previously monitored increasing l attributed to ieaking plugs.
redJction in baseline Isakage. Plug repairs resulted in a significant with a high potential for high cycle fatigue failure was performed toAddition improve the resistance of the OTSG tubes to leakage.
Allowing GPU Nuclear the option to increase the gross leak rate limit to 0.2 gpm above baseline when the increase in leak rate is judged to be i
caused by leaking plugs or joints will not impact plant safety.
This change does not impact the capability to withstand a MSLB accident because the tube leakage limitation of 0.1 gpm above baseline remains in effect.
This chcoge also does not affect the potential radiological consequences of the tube rupture analysis in the FSAR.
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i During normal plant operation if the increasing leakege rate trend is judged to be due to leaking plugs or joints, the new 0.2 gpm upper limit would be invoked. The determination will be documented and made available
'for NRC review upon request.
Under this condition, there will also be continued, close monitoring of the leak rate trend.
When the leak rate exceeds 0.2 gpm, the operators will shut the unit down.
The plant may be shut down before the 0.2 gpm limit is reached if trending indicates that the increase in the P/S leakage may exceed the 0.2 gpm limit in a short time period.
Since the 0.1 gpm leak rate limit for a tube leak remains in effect, the tube integrity will not be affected by the change requested by this TSCR.
Based on the above, invoking a 0.2 gpm P/S leakage rate limit when the observed leakage is judged to be caused by leaking plugs or joints will not affect nuclear safety or safe plant operation.
IV. No Sionificant Hazards Consideration GPU Nuclear has d termined that this License Amendment request poses no significant hazards as defined in 10 CFR 50.92 in that operation of THI-1 in accordance with the proposed amendment will not:
1.
Involve a significant increase in the probability of occurrence or consequences of an accident previously evaluated.
Allowing the leak rate limit above baseline to increase from 0.1 to 0.2 gpm when the increase is judged to be caused by leaking plugs or joints, does not challenge the integrity of the OTSG tubes.
The consequence of a potential tube rupture is bounded by the previous analysis in tne TMI-1 FSAR for a double ended tube rupture.
For a tube leak, the current license administrative limit of 0.1 gpm above baseline remains in effect and shutdown is still required for any rapid increa:e in the P/S leakage rate. The MSLB. radiological consequences are bounded by the previous FSAR Analysis based on the 1 gpm tube leak. Thus there is no increase in the probability or consequences of an accident previously evaluated.
2.
Create the possibility of a new or different kind of accident from any accident previously evaluated.
OTSG tuba rupture or an MSLB accident are the cnly accidents requiring consideration based on this change. Allowing the leak rate i
limit above baseline to increase from 0.1 to 0.2 gpm when the i
increase is caused by leaking plugs or joints will not create a potential to affect the structural integrity of the tubes.
No other j
tube-failure mechanisms are created by this change. This change i
modifies, under restricted conditions, an administrative restriction on plant operation and does not affect any safety system.
Therefore, i
the possibility of a new or different kind of accident from any accident previously evaluated is not created. 2
3.
Involse a significant reduction in a margin of safety.
The plant license currently precludes operation in excess of 0.1 gpm above the baseline leak rate.
If, after shutting down, the source of leakage cannot be located, it is permitted to re-establish a new baseline under these :ircumstances. However, under no circumstance may the leakage limit of I gpm (TS Section 3.1.6.3) be exceeded for t
both steam generators..
This TSCR does not change the 1 gpm limitation.
In order for the increased leak rate limit of 0.2 gpm to be invoked, the increased leakage trend must be judged to be caused by leaking plugs or joints and not be Indicative of rapid tube failure, if P/S leak rate indicates tube leakage exceeds 0.1 gpm, or shows a rapidly increasing
-trend, plant shutdown is still. required. Therefore, there is no significant reduction in the margin of safety.
V.
Imoleme;tation it is requested that the amendment authorizing this TSCR be issued by July 30, 1992 and be effective upon issuance in order that we may be able to implement the change during the current operating cycle.
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