ML20151Z725
| ML20151Z725 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 09/16/1998 |
| From: | Jain S DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-04, GL-97-4, L-98-183, NUDOCS 9809220093 | |
| Download: ML20151Z725 (8) | |
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(M Beave Valley Power Station Shippingport, PA 15077 0004 SUSHiL C. JAIN (412) 393-5512 ggf;*,P ggpgggggy}g,}ggg Fax (724) 643 8069 ident Nuclear Power Division L.98-183 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001
Subject:
Beaver Valley Power Station, Unit No.1 Docket No. 50-334, License No. DPR-66 Response to Request for Additional Information Generic Letter 97-04 ECCS & Containment Heat Removal Pump NPSH This letter provides our response to an NRC request for additional information (RAI) dated August 17,1998, describing the containment overpressure needed to assure adequate net positive suction head (NPSH) for the Emergency Core Cooling and Containment Heat Removal Pumps in relation to the current licensing basis.
The RAI concerns our response to Generic Letter 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps."
Our response to the genetic letter was dated January 6,1998, and supplemented by letter dated July 15, 1998. In the NRC RAI, the NRC staff was concerned that Beaver Valley Power Station Unit No. I may not be within its licensing basis because it appeared that the containment overpressure needed to assure adequate NPSH was greater than the overpressure previously approved by the NRC staff.
l Teleconferenecc with the NRC staff subsequent to the issuance of the RAI revealed that
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this concern was specific to the Low Head Safety Injection (LHSI) pumps at Unit No.1.
Response
The term " overpressure" with respect to NPSH analyses for pumps which take suction from the containment sump can be defined in several ways. Generally, it is defined as pressure above either the saturation pressure of the sump water, or pressure above a defined starting point. Normally, this would be the initial pressure assumed at the start of the transient. In the case of Beaver Valley Unit 1, this pressure will be below d
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Beaver Valley Pcwer Station, Unit No. I and No. 2 Response to Request for Additional Information Generic ~.?,er 97-04 ECCS & Containment Heat Removal Pump NPSH Page 2 atmospheric pressure.
For the purposes of this discussion, " overpressure" will be defined as the amount that the actual total pressure in containment is above the initial l
pressure at the start of the transient.
l The basic equation for available NPSH is as follows:
NPSHa = h static + h suction - h loss - h sat where:
h static = static height of water above pump suction h suction = absolute pressure at the pump suction source (containment) h loss = piping head losses between the suction source and the pump h sat = saturation pressure of the fluid being pumped (based on fluid temperature)
Note that in the above equation, if h sat is assumed to be the same as h suction, (saturated sump model) the terms cancel out and NPSH is only a function ofline losses and static water level. This conservative approach is suggested by the Standard Review Plan for containment heat removal pumps during the recirculation phase. This approach allows no credit for sub-cooling of the sump or containment total pressure above the saturation pressure of the sump water (overpressure).
The regulatory position in Regulatory Guide (RG) 1.1 contains similar wording which states that pumps should not rely on pressure above the initial pressure in order to meet NPSH requirements.
Section 6.3 of the Standard Review Plan (SRP) recommends that the ECCS design should conform to the requirements of RG 1.1. SRP, Section 6.2 allows for credit of containment overpressure for containment heat removal pumps for subatmospheric containments during the injection phase. Reference it, made to assuring that calculations of containment pressure and sump water temperature have been conservatively used in the NPSH evaluation. During the recirculation phase, it is recommended that the design
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analyses conform to RG 1.1.
Beaver Valley Unit I uses the LOCTIC computer program to calculate available NPSH I
for the Recirculation Spray (RS) and LHSI pumps. The LOCTIC computer program, which is also used for containment integrity analyses, has the capability to calculate containment total pressure, containment temperature, sump temperature, and sump water level separately. With these calculated values and an input for the pump suction piping and screen losses, the available NPSH is calculated on a transient basis within the program. Certain features of the program are activated to maximize sump temperature
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Beaver Valley Power Station 0 Unit No. I and No. 2 Response to Request for Additional Information
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Generic Letter 97-04 ECCS & Containment Heat Removal Pump NPSH Page 3 i
and minimize containment pressure during NPSH analyses for conservatism. The results of the analysis provides a time history of available NPSH which factors in the transient i
nature of the sump level and temperature and containment pressure. The calculation of i
NPSH in this manner is explicit based on the containment conditions. No general assumption of containment pressure (or overpressure) is made.
l 5
For both ae RS and LHSI pumps, conservatisms are employed to ensure that the i
containment pressure is minimized relative to the sump vapor pressure. Since these two l
parameters are linked thermodynamically to some degree for a particular transient, it is i
not realistic to use the worst case values for different system or initial conditions; i.e.,
the types of conditions which maximin sump temperature also tend to increase containment pressure. Therefore, a sensitivity study approach was used to establish the l
limiting conditions in terms of Refueling Water Storage Tank (RWST) temperature, j
River Water temperature, single active failures, break location, break sim, condensation l
heat transfer coefficients, and direction of uncertainty on RWST switchover setpoints.
Additionally, initial conditions are set to the most conservative values to minimim calculated available NPSH for both sets of pumps. These include minimum allowable partial air pressure and maximum allowable containment air temperature.
- Also, maximum Quench Spray flows are used to minimim the time to switchover, and the pressure flash method and 100 percent spray thermal efficiencies are used to minimia j
containment pressure and to maximia heat transfer to the sump. Finally, for NPSH j
analyses, no heat transfer from the sump to the containment atmosphere is allowed. This j
information was provided to the NRC in response to a request for additional information j
in May of 1978 (Reference 4).
i The initial NPSH calculations for the LHSI pumps at Beaver Valley Unit No. I credited i
containment pressure. The FSAR, Amendment 17, stated that the NPSH for these pumps was determined from the containment water level and the pressure drop in the suction piping from the sump. The response to FSAR Question 15.55 in the initial licensing phase for Unit I stated that for the RS pumps, the NPSH analyses were performed on a transient basis and took exception to RG 1.1. In 1977, several issues were raised relative to the analyses particularly for the RS pumps initially and later for the LHSI pumps. In a November 17,1977 submittal to the NRC, a report describing system modifications and supporting analyses for containment integrity and NPSH analyses was provided (Reference 3). The report describes the use of the LOCTIC program for calculating NPSH for both the LHSI and RS pumps. Based on the description provided, and subsequent questions and responses conceming the information, it is clear that containment " overpressure" was being credited for both the RS and LSHI pumps. In August of 1980, the NRC issued a Safety Evaluation Report (SER) associated with the proposed system changes and technical specification changes. This SER found that the
4 Beaver Valley P:wer Station, Unit No. I and No. 2 j
Response to Request for Additional Information l
Generic Letter 97-04 ECCS & Containment Heat Removal Pump NPSH
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Page 4 NPSH analyses presented were arcy-kle. A confirmatory analysis of the containment pressure and sump temperature performed by the NRC was cited as evidence of the acceptability. Containment pressure and sump temperature are only relevant when the analyses credit " overpressure."
Based on this, it has been our understandmg that the SER provided NRC approval of the l
methodology utilized for calculating available NPSH. No specific values of overpressure l
credited were noted in the SER. Overpressure (required or available) could have been j
calculated from information provided in the 1978 submittal based on the transient results provided for containment pressure, sump vapor pressure, available NPSH and sump water level. However, no specific discussion of overpressure (required or available) was contained in the submittal or the SER.
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Revisions to the NPSH analyses have been made over the time period since the SER was j
issued in 1980. These have been performed in response to various changes in relevant inputs to the analyses. Most notably, the River Water temperature limits were raised in j
1989 and most recently suction piping pressure drops were revised slightly for the LHSI pumps based on comments during a Duquesne Light Company Safety System Functional Inspection in 1995. Based on these changes, the " overpressure" reiluired to meet NPSH limits for LHSI has increased. This is primarily due to increased sump temperature during the transient. Offsetting this to some degree, the calculated containment pressure also increased. A comparison of the current parameters for the LHSI pumps versus those derived from the 1978 submittal is shown in the attached figures for the limiting NPSH i
case.
These figures show comparisons of the containment total pressure, sump
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temocriure, and required " overpressure" to meet NPSH limits.
Based on the above discussion, Duquesne Light believes that Beaver Valley Unit No.1 4
is within its current licensing basis. Credit for conminment overpressure to meet NPSH requirements has been utilized in the design for both the RS and LHSI pumps, and the methodology for performing this analysis was reviewed by the NRC.
That same i
methodology is used for the current analyses of record. Changes to the analyses have been performed under 10 CFR 50.59 without resulting in an unreviewed safety question l
based on the fact that the approved methodology was being used for the analyses and while this methodology credited " overpressure," no specific value had been explicitly approved by the NRC.
j Sincerely, 5
M'W Sushil C. Jain
Beaver Valley Power Station, Unit No. I and No. 2 Response to Request for Additional Information Generic Letter 97-04 ECCS & Containment Heat Removal Pump NPSH Page 5 c:
Mr. D. S. Brinkman, Sr. Project Manager Mr. D. M. Kern, Sr. Resident InWor Mr. H. J. Miller, NRC Region I Administrator.
References:
- 1. NUREG 0800 Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants
- 2. _ NRC Regulatory Guide 1.1 Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal System Pumps
- 3. C. N. Dunn to R. W. Reid letter dated November 17, 1977 Analysis and System Modifications for Recirculation Spray and Low Head Safety Injection Pumps Net Positive Suction Head
- 4. C. N. Dunn to A. Schwencer letter dated May 16,1978 Partial Response to Request for AdditionalInformation
- 5. Safety Evaluation by the Office ofNuclear Reactor Regulation related to Amendment No. 28 to Facility Operating License No. DPR-66 dated August 27,1980
- 6. Duquesne Light letter L-97-049 dated November 6,1997 (response to NRC Genenc Letter 97-04)
- 7. Duquesne Light Company Analysis 8700-DMC-2339
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