ML19347E164
| ML19347E164 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/20/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8104240157 | |
| Download: ML19347E164 (6) | |
Text
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 400 Chestnut Street Tower II April 20, 1981 N
Dimotor of Nuclear Reactor Regulation g.
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Attentions ler. A. Schwencer, Chief ar,4 Bg h
/8g7A Licensing Branch No. 2 3
Nh Division of Licensing U.S. Nuclear Regulatory Cosmaission F
Washington, DC 20555 V
m Dear Mr. Schwencer In the Matter of the Application of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 Enclosed is the information requested by your letter dated April 14, 1981, regarding centrifugal charging pump miniflow isolation at Sequoyah Nuclear Plant.
l If you have any questions, please get in touch with D. L. Lambert at FTS 857-2581.
Very truly yours, TENNESSEE VALLEY AUTHORITY M
. H. Mills, W r Nuclear Regulation and Safety sworn to and subsor y before me thia 48 6 k y of ( M 1981 N2sc$ l M,
Notap Public f
l My Commission Expims 8 / 88 Enclosure
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v ENCLOSURE SEQUOYAH NUCLEAR PLANT RESPONSE TO NRC QUESTIONS REGARDING CENTRIFUGAL CHARGING PUMP MINIFLOW ISOLATION 1.
(a) The Technical Specifications fcr Sequoyah 1 require the pump discharge pressure with recirculation throughout the miniflow line to be at least 2400 psig, whereas a discharge pressure of over 2600 psig might be expected from the FSAR. What is the basis for the value in Technical Specifications?
_t (b) For each centrifugal charging pump, provide information on the allowable ranges of pump head and/or flow and the initial reference values (see Table IWP-3100-2, IWP-3210) that will be used for the Section XI inservice tests.' Is a lower limit for the reference value specified?
(c) Provide information on the allowances for pump degradation used in the safety analysis and describe how it is confirmed that this allowance is within that corresponding to pump limits allowed by the Technical Specifications and the Section XI tests for Sequoyah 1.
Response
2 A.
The technical specification value of 2400 lb/in g discharge pressure at the miniflow condition was based on a Westinghouse Electric Corporation survey taking the worst case performance experienced and degrading the pump head at miniflow by 5 percent. This 5-percent degradation resu ted in a minimum expected discharge presegre of 2400 lb/in}g.
The curve used to obtain the 2400 lb/in g 'is the worst case curve degraded by 5 percent while the design values listed in the FSAR on Table b.3-1 are the nominal values for the Sequoyah Nuclear Plant pumps.
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B.
For the crntrifugal charging pumps (CCP's) at Sequoyah unit 1, the reference values and their allowable ranges of pump head are established and checked periodically by Surveillance Instruction (SI) 40.
The initial reference values can be established either by the system preoperational test or the first performance of the SI.
Following maintenance on the pumps which might effect its performance, the reference values are reestablished by the procedure outlined in SI-40.
If the new reference values are lower than the previous reference values, the previous reference values and allowable limits are retained for pump performance acceptance criteria.
If the new values are higher than the previous values, the new values are the new acceptance criteria. At Sequoyah, this surveillance procedure is performed chile the pumps are in the recirculation
~~ miniflow mode of operation.
In the case of SI-40, the acceptable allowable ranges of pump heads are established as per ASME B&PV code section XI, table IWP-3100-2, which requires the allowable ranges to be from 0.93 AP O R (O R s th R
measured reference pump head).
Currently, the allowable ranges of inservice test quantities for the Sequoyah unit 1 CCP's are:
Parameter CCP1 -A CCPIB-B Suction pressure, PL
> 11.6 lb/in a
> 11.6 lb/in a 2
Discharge pressure, Po
> 2400 lb/in g
> 2400 lb/in g AP (Discharge - Suction) 2327.3 to 2552.6 lb/in
'2392.0 to' 2623.5 lb/in k
The reference value, AP, is established by the above allowable range R
of AP.
A lower limit for the value of AP is not specifically g
established; however, the technical spec 111 cation limits the lowest acceptable value.
C.
From the Final Safety Analysis Report ~(FSAR) and Westinghouse Bulletin NSD-TB 80-11, the basis for the emergency core cooling system (ECCS) performance analysis used in the FSAR is the 2
same basis which results in the 2400 lb/in g discharge pressure required by the technical specification at miniflow. The safeguard pump curves used to generate the FSAR-related information are obtained by degrading the worse case vendor-certified pump curves by 5 percent of its certified design total developed head at the design point applied uniformly on the pump curve. This analysis was made with assumed instrument accuracies of i 1 percent for static pressure instrumentation and i 4 percent for orifice and AP instrumentation. This degradation method results in safety analysis pump curves essentially the same shape as the worse case curve.
Since the degradation value was taken at the design point (150 gpm, 5800 f t.),
this same value would result in a less than 5-percent degradation at the miniflow point 2. Thus, the technical specification value of 2400 lb/in g and the FSAR analysis value are the same and both are within the 93-percent low limit specified by the ASME B&PV Code section XI, table IWP-3100-2.
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2.
In IE Bulletin 80-18, Item 2.d requires justification that " flow available from the CCPs with the modifications in place will be sufficient to justify continued applicability of any safety related analyses which take credit for flow from the CCPs (LOCA, HELB, etc.)."
For the small break LOCAs, the submittal refers to a reduced _ safety injection flow rate of 45 gpm at 1250 psia because of the open miniflow line. However, since there are no plant limits on flow through the miniflow line, the actual flow rates at a given plant might be appreciably larger than this value due to errosion or sizing of the restricting orifice. Provide tests results for Sequoyah 1 to confirm -
that the flow rate is within the assumed limits.
Response
Sequoyah unit 1 miniflow rates on recirculation were measured by the preoperational test SQN W6.1C.
This test consisted of pumping through the miniflow orifice plate to the volume control tank (VCT)'
and recording the time needed to cause a given level change. The Sequoyah unit 1 preoperational test indicated the miniflow for both pumps Was approximately 73 gpm at 3 ischarge pressure of 2530 d
2 lb/in g for pump 1A and 2600 lb/in g on the 1B pump.
I The above value taken at the indicated discharge pressures corr 3sponds to-approximately 51.0 gpm at the reduced pressure of 1250 lb/in a assumed in the Westinghouse evaluation.
Westinghouse has indic3ted that their evaluation, assuming 45 gpm miniflow at 1250 lb/in a, would not be significantly changed due to Sequoyah's slightly higher miniflow of 51 gpm.
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For. the small break LOCAs (2" less ghan diameter less than or equal to 6") it is stated that there is a 10 F PCT penalty if miniflow isolation is delayed 10 minutes and a PT penalty of 200 F or more if no miniflow isolation occurs. For the larger break sizes (6" less 'than diameter) it is stated that a 10 minute delay in miniflow isolation results in a PCT penalty of 40 F. - What PCT penalty results if no miniflow isolation occurs? What are the PCTs corresponding to the above PCT penalties?
Response
No sensitivity studies have been developed on the effects of variations in ECCS flow for UHI plants.
In the Westinghouse safety evaluation, faformation was derived from studies done on a 3-loop klant with no intermediate range safety injection pumps. This information was utilized to develop a~best engineering evaluation for peat. clad temperature penalties for the UHI plant.
This evalur. tion concluded the the PCT's quoted for the non-UHI plant were bounding for a UHI plant; therefore, for the case in which the air.iflow is isolated when the reactor coolant pumps are tripped, pagligible impact on PCT would result.
For the case in which the miniflow is isolated at 10 minutes, the 40 F PCT penalty is believed to be bounding. For the case in which no miniflow isolation takes place, the 200 F PCT' penalty is believed to be bounding. The reasons for this opinion are that:
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o 4.
Provide larger copies of FSAR figures 9 3-13 and 9 3-20.
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. Response Larger copies of these FSAR figures were provided to the NRC staff reviewer
'in' February 1981.
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