ML20044E718
| ML20044E718 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 05/18/1993 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9305250354 | |
| Download: ML20044E718 (4) | |
Text
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10CFR50.55a(g)(5)(1ii)
PIIILADELPHIA ELECTRIC COMPANY l
NUCLEAR GROUP HEADQUARTERS 955-65 CHESTERBROOK BLVD.
WAYNE, PA 19087 5691 (215) MO-6000 STATION SUPPORT DEPARTMENT May 18, 1993 i
Docket Nos. 50-352 50-353 License Nos. NPF-39 NPF-85 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Limerick Generating Station, Units 1 and 2 Relief Request for the First Ten Year Interval Pump and Valve Inservice Testing Program Gentlemen:
Attached for you review and approval is Relief Request No. 51-VRR-2 for the Limerick Generating Station (LGS), Units 1 and 2, First Ten Year Interval Pump and Valve Inservice Testing (IST) Program. Relief Request No. 51-VRR-2 requests relief from the American Society of Mechanical Engineers (ASX'c) Boiler and Pressure Vessel (B&PV) Code Section XI, Subsection IWV requirement regarding exercise testing of check valves in the forward direction.
This relief reque:t applies to the minimum flow (min-flow) check valves located in the min-flow line for the Residual Heat Removal (RHR) system pumps for Units 1 and 2.
These min-flow check valves have an active safety position in the open direction to permit low flow recirculation to the suppression pool in order to protect the RHR pumps from potential damage during low pump flow conditions.
Full exercise testing of these valves in the forward direction requires confirzation that the disc moves away from the seat as stipulated by ASME B&PV Code requirements; specifically,Section XI, Subsection IWV, Article IWV-3522(b).
These valves are not equipped with a position indicating device or have observable means (i.e., a lever) to confirm disc position.
In lieu of performing exercise testing in accordance with Code
-i requirements, we propose that full stroke exercise testing of the RHR min-flow check valves in the forward direction will be accomplished by indirectly verifying that RHR design min-flow rate is passed though each valve. Flow will be obtained via conversion of a pressure signal utilizing a reference pump curve.
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U.S. Nuclear Regulatory Commission May 18, 1993 Document Control Desk Page 2
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c We would appreciatt your cooperation in providing an expeditious review of this relief request since full flow test verification of these valves by visual means is not possible.
These valves are required to be tested on a quarterly e
basis.
If you have any questions or require additional information, please do not hesitate to contact us.
Very truly yours, i
G. A. Hunger, Jr.
Director Licensing Section Attachment cc:
T. T. Martin, Administrator, USNRC, Region I (w/ attachment)
N. S. Perry, USNRC Senior Resident Inspector, LGS (w/ attachment) l
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10 CFR 50.59 Review-for IST Program Relief Request t
SI VRR-2, Rev. O Attachment I Relief Request No. SI-VRR 2, Rev. O f
System:
Valve (s):
51-1FD46 A,B,C,D 51-2F046 A,B,C,D I
Category:
C I
i Function:
RHR Pump Min-Flow Check Valves f
I Testing Requirements: Exercise in the forward direction i
Ilasis for Relief:
These valves are located on the RHR min. flow line and have an active safety j
position in the open direction to permit low flow recirculation to the suppression pool in order to protect the RHR pumps from potential damage associated with low pump flow. Full stroke exercising these valves in the forward direction requires confirmation that the disc moves away from the seat per ASME Section XI Code, Subsection IWV, Article IWV-3522(b). These valves are neither equipped with a position indicating device nor provided with an observable mechanical means _(i.e.
lever) to confirm disc position. Therefore, full flow test verification of these valves by visual means is not possible.
Two othei methods exist to confirm full stroke of check valves to the open position.
The first method is to verify that the design flow rate is passed through each valve as discussed in NRC Generic Letter 89-04, Attachment 1, Position 1. The second
-3 method is to employ 'other positive means" such as acoustic monitoring of the valve disc position. Both of these methods satisfy the intent of IWV-3522(b).
l Three alternatives were irzestigated related to the flow verification method. Each of these alternatives quantifies flow through the RHR min-ilow line.The alternatives are (1) indirect flow measurement.ia conversion of a pressure signal utilizing a reference pump curve,(2) addition of test taps and associated flow indie:. tion desices immediately upstream and downstream of the RHR min-flow orifices, and (3) use of ultrasonic flow meters.
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t Alternative (1), indirect flow measurement via conversion of a pressure signal utilizing a reference pump curve is the most practical and cost effective option and provides a level of quality and safety equivalent to the testing prescribed in ASME IWV-3522(b) and NRC Generic Letter 89-04, Attachment 1, Position 1. An RHR i
pump is run with its respective min-flow isolation valve HV-51-1(2)F007 A,B,CD in the open position and all other RHR pump discharge piping paths isolated.
Assurance that all flow is diverted to the min-flow line is provided since all other discharge paths are either equipped with double isolation valves, are local leak rate '
tested (LLRT) or are boundary LLRT valves, or are equipped with isolation valves that are opposed by higher (reactor) pressure, except for the RHR cross-tic line.
The RHR cross-t!c line is equipped with'a singic isolation valve HV4 L '1(2)82A,B that is locked closed and rarely stroked which provides a high col.Jdence that-i negligible leakage passes through the valve. The design minimum flow rate for RHR is 1000 gpm which is 10% of rated RHR system flow. The preservice testing pump i
I l
curve, which is field-validated in the low flow region, is utilized to determine the corresponding pump differential pressure associated with the minimum flow value.
Next, the pump suction pressure which is determined from suppression pool level (Ref GPRR-4) is added to the min flow differential pressure to obtain the maximum i
allowable discharge pressure corresponding to achieving the min-flow rating. This value is then converted to a voltage value via calculation based on the pressure-voltage ranges of the RHR discharge pressure transmitter PT-51-1(2)N055 A,C.E,G.
The resultant voltage is the maximum allowable discharge pressure-voltage associated 1
with the mm-flow rating. Herefore, this voltage value becomes the check valve exercise test acceptance criteria.
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The actual pump discharge pressure is determined by measuring the output voltage at pressure transmitter PT-511(2)N055A C,E,G with a voltmeter. This voltage is compared to the aforementioned maximum allowable discharge pressure-voltage to verify the passing of the design flow rate through the valve. The actual pressure-voltage must be equal to or less than the maximum allowable pressure-voltage in order for an acceptab!c exercise test. Otherwise, the exercise test is unacceptable.
The presenice testing pump curves will be re-validated prior to the next RHR min-r flow test. The curves will be verified (a) from zero flow (shut-off head) to approximately 2 times the minimum flow rating using a total of 3 data points and (b) at the reference full flow ccmdition. Pump curve veriiicatica will be accomplished using pressure instruments PT-51-1(2)N055A,C,E,G for pressure readings and flow instruments FY-51-1(2)K600A,B,C,D and FT-51-1(2)N052A,B,C,D for flow readmgs.
i These instruments meet IWP-4100 accuracy requirements. The pump curve is also partially field-validated quarterly at the reference full flow value during the pump insenice test.
Alternative (2), addition of test taps and associated flow indication devices immediately upstream and downstream of the RHR min-flow orifices requires a plant modification for implementation. This option would impose a capital burden on the j
facility without a compensating increase in the level of quality and safety since alternative (1) provides a method which satisfies IWV-3522(b).
Alternative (3), use of ultrasonic flow meters has been attempted and yielded erratic and erroneous results. The flow characteristics of the fluid in the RHR min-flowline are not amenable to ultrasonic flow measurement. The combination of high flow velocities and pipe configuration produce turbulent flow conditions which are not compatible with ultrasonic flow instrumentation. The optimum pipe location (straight pipe section) for mounting the ultrasonic flow instrument was utilized during testing. This method is used in other applications at LGS but has not been successful with the RHR min-flow test.
An alternate exercise test method utilizing "other positive means" was also i
considered. This alternative employs acoustic monitoring as a non-intrusive test method to record an acoustic signal of the check valve disc achieving full open
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position. PECo has established a check valve monitoring program. This program, although in place is still evohing. A high confidence level exists in the closed direction check valve acoustic signatures. However, the confidence level in the open direction check valve signatures is insufficient to assure that the design flow rate i
and/or full open position has been achieved.
Alternate Testing:
Full stroke exercise testing in the forward direction will be accomplished by indirectly verifying that the RHR design min-flow rate is passed through each valve. Flow will he obtained via conversion of a pressure signal utilizing a reference pump curve.
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