ML19338G045
| ML19338G045 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom, Limerick  |
| Issue date: | 10/24/1980 |
| From: | Gallagher J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8010280372 | |
| Download: ML19338G045 (7) | |
Text
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PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET P.O. BOX 8699 PHILADELPHI A. PA.19101 JOSEPH W. GALLAGHER
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(215)841 5003 stacTaic enooucv on osemusar October 24, 1930 Mr. Darrell C.
Eisenhut, Director Division of Licensing US Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
HPCI/RCIC Initiation Setpoint
References:
- 1) Letter dated May 7,
- 1980, D.
G.
- Eisenhut, NRC, to All Operating Reactor Licensees
- 2) Letter dated October 2,
- 1980, J.
N.
Gallagher Philadelphia Electric Co.,
to D.
G.
- Eisenhut, Nuclear Regulatory Comaission
Dear Mr. Eisenhut:
The Nuclear Regulatory Conmission proposed in ite.1 II.K.3.13 of reference 1, a nodification for consideration by each licensee.
The proposal involves separation of the HPCI and RCIC initiation levels so that the RCIC system initiates at a higher water level than the RPCI system.
ThL intent of this chan 3 is to reduce the number of challenges to the HPCI systen, and subsequently reduce stress on the vessel fron cold water injection.
The NRC requested an evaluation by October 1, 1980 of the proposed modification.
In reference 2, we proposed a submittal date of October 24, 1980 for providing the bases for our conclusions on this issue.
Therefore, after a final review of the BUR Owners' Group report previously submitted to the NRC, we endorse this evaluation as the bases for our conclusions, and enclose a copy for your information.
The General Electric Company, on behalf of the 3WR Owners' Group, submitted the evaluation regarding this proposal to the NRC on October 1,
1930.
Personnel from Philadelphia Electric Company participated on the Owners' Group subcommittee responsible for working with the General Electric Company to develop and review the results of this study.
As stated in reference 2,
it is the conclusion of the BUR. Owners' Group and of Aco/
s s o20280 37L
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Mr.. D a r r e l l' C '. Eisenhut, Director Page 2
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'an independent ssessment by the Philadelphia Electric Company's technical staff that setpoint. changes will yield minimal
. reduction in the thermal cycle history.
Additionally,: separating I
the itPCI/RCIC setpoints-will have undesirable consequences as l
discussed in the-October 1, 1980 Owners' Group letter, which outweigh the. benefit of the limited reduction in thermal cycles.
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Should you have any questions regarding this matter, please do.not hesitate to contact us.
l Very truly yours, U h_ A_0 1j I
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GENER AL h ELECTRIC NUCLEAR POWER SYSTEMS DIVISION GENERAL ELECTRIC COMPANY,175 CURTNER A*/E., SAN JOSE, CAUFORNIA 95125 O
M/C 682 (408) 925-1822 October 1, 1980 U. S. Nuclear Regulatory Commis:fon Division of Licensing Office of Nuclear Reactor Regulation Washington, D. C.
20555 Attention:
D. G. Eisenhut, Director Gentlemen:
Subject:
NUREG-0660 Requirement II.K.3.13 This letter transmits an evaluation performed oy General Electric on behalf of the BWR Owners Group of NUREG-0660 recommendation II.K.3.13.
The attached report presents the analyses, conclusions
,and recommendations regarding separation of the initiation levels of the High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) systems.
If you have any further questions regarding the BWR Owners Group response to NUREG-0660 requirement II.K.3.13, please contact Mr. S. J. Stark (408) 925-1822 of my staff.
Very truly yours,
$.k J
R.u.T h La e
y R. H. Buchholz, Manager BAR Systems Licensing Safety and Licensing Operation Attachment i
.cc:
J. A. Olshinski P. W. Marriott M. W. Hodges
- 0. B. Waters D. F. Ross BWR Owners Group 2'dLL d> $ 35 </6/
EVR.UATXON OF PROPOSED MODIFICATION TO HPCI and RCIC OPERATION I.
Jntroduction-1 This report has been prep 3 red as the BWR Owners' Group generic response to NUREG-0660 task item I).K.3.13 which addresses the operation of the High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) systems. The text of this requirement is as follows:
Currently, the reactor core isolation cooling (RCIC) system and the high p*. aure coolant injection (HPCI) system both initiate on the sarra low water level signal and both isolate on the same high water level signal. The HPCI system will restart on low water level but the RCIC system will not. The PCIC system is a
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low-flow system when conwed to the HPCI system.
The initiation levels of the HPCI and
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- ,jstem should be separated s a tha t the RCIC system initiates a., a higher water level than ti.e HPCI system.
Further, the RCIC system initiation logic should be modified so that the RCIC system will restart on low water level.
These changes have the potential to reduce the number of chal-lenges to the HPCI system and could result in less stress on the vessel from cold water injection. Analyses should be performed to evaluate these changes. The analyses should be submitted to the NRC staff and changes should be implemented if justified by the analyses.
!I.
Conclusions This report presents the analyses, conclusions, and recommendations regard-ing separation of the initiation levels of the HPCI and RCIC systems.
As previousl erence 1)y conf.irmed by discussions with the staff on June 13 and 17 (Ref-
, the fundamental issue of the separation requirement is the potential benefit of reducing the number of thermal cycles on the reactor vessel and internals resulting from HPCI operation. Thus, the evaluation which follows concentrates on thermal cycle analyses of RCIC and HPCI system operation.
The most severe thermal cycle due to RCIC and HPCI initiation at the current lowwaterlevel setpoint is assessed and compared to the thermal cycle analysis for the limiting reactor components.
Operating plant ex-perience is evaluated to estimate the frequency of occurrence of HPCI and RCIC initiations.
Based on the foregoing, it is concluded that the current design is satisfactory, and a significant reduction in thermal cycles is not necessary.
The potential for reducing thermal cycles by separating the RCIC and HPCI initiation setpoint is also examined. The results of these analyses indi-cate that no significant reduction in thermal cycles is acMevable by sep-l arating the setpoints.
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- 11. Conclusions (cont)
An analysis which evaluates the proposed logic change for the RCIC system autcmatic reset / restart has also been completed. This evaluation concludes that such a change would be both beneficial and achievable. This analysis and conclusion will be documented in a separate report as discussed in a telecon with the NRC (Reference 2).
III. Evaluation of Thermal Cycles due to HPCI and RCIC Actuation The analyses presented are for typical BWR/3 and 4' designs where the HPCI and RCIC systems inject via the feedwater spargers.
Later plant designs (BWR/S and 6) have separate injection locations for the,RCIC and HPCI/HPCS systems and are less limiting in comparison to the typical BWR/3 and 4 configuration.
Differences in the thermal fatigue analyses are identified where appropriate.
Chapter 15 of the Final Safety Analysis Report (FSAR) examines postulated lant transients.
Examination of these events has identified transients which result in the loss of feedwater, including the loss of feedwater transient, as resulting in the most limiting thermal cycle due to HPCI and RCIC actuation.
The portions of the reactor vessel and its internals which may be affected by operation of HPCI and RCIC are the reactor vessel shell, core shroud, and feedwater nozzles and spargers. Thermal fatigue analyses show that the i'miting reactor component is the feedwater nozzle for all plants equipped w;th HPCI and RCIC systems. The feedwater sparger is exposed to thermal c.'cles resulting from HPCI and RCIC operation as well as feedwater tempera-ture changes during daily and weekly power swings.
HPCI/HPCS and RCIC in-jection locations on plants that do not inject through the fe dwater system o
are not exposed to temperature variations, during daily and wekly power swings.
Upon loss of feedwater, the temperature oh the feedwater sparger and thr.
nozzles approaches the normal reactor operating temperature.
Initiation of HPCI and RCIC at low water level then cools the sparger and nozzle. The most severe thermal cycle identified by anlaysis results in a temperature change from 5500F (reactor operating temperature) to 500F (HPCI/RCIC injec-tion temperature). This temperature change is included in the loads assumed in fatigue analysis based on normal operation (which itself includes many cold water injections) as well as expected Mansients and other postulated The duty imposed on the feedwater no.:zle from all causes is summed events.
to obtain a calculated fatigt.e usage of 0.95, which is less thn the limit of 1.0 The design basis includes 70 thermal cycles due to HPCI and RCIC injection of the type described. The calculated fatigue usage of these cycles is 0.16, or about 177, of the total fatigue usage. An evaluation for plants with other RCIC and HPCI/HPCS injection locations results in a calculated total fatigue usage of less than 0.2.
It should be noted that there is no significant thermal effect on the reactor vessel shell due to the operation of HPCI and RCIC for any plant configuration.
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III. Evaluation of Thermal Cycles due to HDCI and RCIC Actuation (cont)
Operating plant experience indicates an average of approximately 1.5 RCIC and HPCI actuations per year per plant.
Even if every actuation resulted in the most severe thermal transient described earlier, the thermal analysis has shown that the design is within the fatigue limit.
Therefore, the current design 1s conservative and minimally effected by HPCI and RCIC actuation due to loss of feedwater events for all.)! ants with HPCI/
IV.
Evaluation of the Potential for Reducing Thermal Cycles by Separation of HPCI and RCIC Initiation Setpoints The discussion that follows addresses the potential for reducing the thermal cycles due to HPCI and RCIC initiation. The transients con-sidered are !. hose cited in FSAR Chapter 15.
Two classes of transients can cause RCIC and HPCI initiation:
1.
Initi3ti0n of HPCI and RCIC on low water level after feedwater is tripped on high reactor water level.
For these trans.ients, the inventory is slowly lost due to decay heat steam generation.
2.
Initiation of HPCI and RCIC following a sudden loss of feedwater.
For these transients, inventory loss is rapid with HPCI and RCIC initiation occurring approximately 20 seconds after event initiation.
The majority of transients from Chapter 15 which require HPCI and RCIC initiation can be grouped into Category 1.
In this case, the level de-crease is slow because of the low power condition at the time the feed-water is tripped. A small amount of makeup water is needed and if feed-water cannot be restored, sufficient time is usually available such tnat RCIC would be started manually as the water level slowly decreases below the normal operating range. Since such manual action has been demon-strated to be successful for avoidance of HPCI actuation, it is considered sufficient and more desirable than an increase of the RCIC setpoint close to the normal operating water level.
If neither feedwater or RCIC is manually started, both HPCI and RCIC would automatically be initiated at ths low level setpoint.
The second class of transient to be considered is the loss of feedwater event. Loss of feedwater flow is accompanied by a large and rapid drop in water level. Low level scram is initiated in approximately 5 seconds, with RCIC and HPCI actuation occurring shortly thereafter. With both systems operating, water level is quickly restored. Due to the rapidity of the transient, HPCI initiation cannot be avoided even if the RCIC set-point is raised to the normal operating level. Therefore raising the RCIC
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setpoint for this type of transient can have no beneficial effect on thermal cycles and will interfere with normal plant operation.
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Evaluation of th, Potential for Reducing Thermal Cycles by Seoaration of HPCI and RCIC Initiation Setpoints (cont)
For both types 'of events, automatic RCIC operation could avoid HPCI initiation if the HPCI setpoint were lowered; however, no significant benefit is realized unless the HPCI setpoint is lowered to near the low-low water level (level 1). Since the actuation of RCIC and HPCI has been previously shown to be of minimal impact in fatigue usage analyses, and lowering of the HPCI setpoint lessens the existing margin for as-surance of adequate core cooling, such a separation of HPCI and RCIC setpoints by lowering the HPCI setpoint is not warranted.
V.
Summary In the foregoing discus 5fon, it has been shown that HPCI and RCIC initiations at the current low water level setpoints is within the design basis thermal fatigue analysis of the reactor vessel and its internals.
Separating HPCI and RCIC setpoints as a means of re-ducing thermal cycles has been shown to be of negligible benefit.
In addition, raising the RCIC setpoint or lowering the HPCI setpoint have undesirable consequences which outweigh the benefit of the limited reduction in thermal cycles.
GE recommends no change in RCIC or HPCI/HPCS setpoints.Therefore, w VI. References 1.
R. H. Buchholz (GE) letter to 0. G. Eisenhut (NRC), Implementation of NUREG-0660 Reouirement II.K.3.13, dated July 11, 1980 (MFN-124-80) 2.
R. H. Buchholz (GE) letter to D. F. Ross, Jr. (NRC). NUREG-0660 Requirement II.K.3.13, dated September 29, 1980 (MFN-167-80) 0 4
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