ML20081A877

Forwards Response to 830828 Request for Addl Info Re N-1 Loop Operation.Any Asymmetries Existing Due to N-1 Loop Operation Have Little or No Impact on Power Distribution,Dnb Limits & Fuel Integrity

ML20081A877
Person / Time
Site:	Beaver Valley
Issue date:	10/21/1983
From:	Carey J DUQUESNE LIGHT CO.
To:	Varga S Office of Nuclear Reactor Regulation
References
TAC-10386, NUDOCS 8310270154
Download: ML20081A877 (10)

Text

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'At3 Telephone (412) 4564000

.O Box 4 Shippingport, PA 15077A104 October 21, 1983 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Attn: fir. Steven A. Varga, Chief Operating Reactors Branch No. 1 Division of Licensing Washingtor., DC 20555

Reference:

Beaver Valley Power Station, Unit No.1 Docket No. 50-334, License No. DPR-66 Request for Additional Information on N-1 Loop Operation Gentlemen:

In accordance with your letter of August 28, 1983, we are providing the information requested on two-loop operation for Beaver Valley Power Station - Unit No.1. We have evaluated the questions submitted by the Core Perfonnance Branch in your letter and provided responses in Attach-ment A.

If you have any questions on this subject, please contact my office.

Very truly yours,

. J. Carey Vice President, Nuclear Attachments cc: !!r. W. fl. Troskoski, Resident Inspector V. S. Nuclear Regulatory Commission Beaver Valley Power Station Shippingport, PA 15077 U. S. Nuclear Regulatory Commission c/o Document Management Branch Lashington, DC 20555

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8310270154 831021 o

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ATTACHMENT A Page 1 of 9 RESPONSES TO NRC QUESTIONS ON THE N-1 LOOP OPERATIONS w

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." . ATTACHMENT A Page 2 of 9 N-1 LooD Operation Item 1 During two-loop operation of Beaver Valley Unit 1, temperature differences in the active cold legs of a few degrees could exist. Therefore, a radial power tilt and increase in enthalpy rise factor could result. Provide the following information for justifying the design for two-loop operation:

1. The method of accounting for differences (if any) in the two and three-loop thermal-hydraulic design: *

Response

l The thermal hydraulic safety analysis performed for N-1 loop operation assumes that the isolation valves are closed. No temperature difference is induced as a result of isolating a loop. The quadrant power tilt is restricted to 2

. percent as stated in the Beaver Valley Technical Specification (Section 3.2.4). Exceeding this value would require the necessary actions as described in the Technical Specifications. Given the above, there is no difference in the thermal hydraulic methodology in evaluating N and N-1 loop operation.

2. Any special monitoring procedures required during two-loop operation:

Response

No special monitoring procedures are required, other than those required for 3 loop operation.

3. .The reactor protective system setpoints related to DNBR protection and how they are generated:

l Response: ,

The reactor protective systerii setpoints were calculated using the methodology l described in WCAP-8745, " Design Bases for the Thermal Overpower AT and Thermal Overtemperature 4T Trio Functions", March,1977.

4. The effects of anticipated operational occurences on the cold leg temperature distribution and how this effect is included in the design:

Response

The safety analysis was performed assuming both the hot leg and cold leg isolation valves are closed. Therefore, no temperature difference in the active cold legs was assumed to occur due to the isolated loop. The safety analysis model is essentially the same as that for a 2 loop plant.

1

ATTACHMENT A Page 3 of 9

5. A thermal hydraulic design comparison table similar to Table 4.4 in the SER for two and three-loop operation. In addition this comparison should include the core pressure drop, the critical heat flux correlation used.

The minimum DNBR limit, the nominal minimum DNBR and design DNBR for the typical and thimble flow channel and design DNBR for the design transient for both the typical and thimble flow channel. What is the design transient?

Response

\ x Table 1 (attached) compares three and two loop operation for Beaver Valley unit 1. There are many transients evaluated for safety analysis.

Descriptions of each are given in the accident analysis section of the FSAR.

Ite.m.II

. Inlet flow maldistribution is a possibility with two-loop operation. Have flow model tests or analytical studies been made for this effect? If so, provide the reference and results and also provide the following information.

Response

As stated in Beaver Valleys FSAR, the core inlet flow maldistribution criteria used in THINC analyses are based on 1/7 scale hydraulic reactor model tests (Ref. 1 and 2). THINC analyses using this data have indicated that a conservative design basis is to consider a 5 percent reduction in the flow to the hot assembly. Studies made with the improved THINC model (Ref. 3) show that it is adequate to use the 5% reduction in inlet flow to the hot assembly for a loop out of service based on the experimental data in Reference 1 and 2.

1. What asymmetries exist (if any) in the core flow due to isolation of one loop? Provide inlet flow distribution maps for two and three-loop l operations.

l l Response:

The inlet flow distributions for two and three loop operation (Ref. 1) for a j single lower internals configuration are attached for comparison.

2. What is the effect of any inlet flow maldistribution on the hot channel DNBR? ,

Response

1

) Studies performed in Reference 3 show that even with a 10% flow reduction into l the center nine assemblies of the core, the hot channel DNBR is reduced by less than 0.5%.

l l

. ATTACHMENT A Page 4 of 9

3. What impact do any asp.netries have on power distribution, DNB limits and fuel integrity?

Response

Any asymmetries that exist due to N-1 loop operation have little or no impact on power distribution, DN8 limits and fuel integrity. Even with extreme inlet flow maldistributions, hot channel enthalpy rise and DNBR are only slightly affected (Ref. 3). Generic radial power distributions and a 5% flow reduction into the hot assembly used in safety analyses account for any inlet flow maldistributions. All restrictions that are placed on the fuel to ensure fuel integrily are applicable to both N and n-1 loop operation. The various criteria that must be met are explained in Chapter 3 of the BVPS Unit 1 FSAR.

4. Provide information on flow instability with two-loop operation

Response

The current model, Reference 4, used in analyzing flow instabilities shows that the margin to the inception of thermohydrodynamic instability increases with a decrease in exit quality. The exit quality for N-1 loop operation is less than that for N loop operation and therefore a greater margin to flow instability exists for N-1 loop operation.

References:

1) G. Hetsroni, " Hydraulic Tests of the San Onofre Reactor Model",

WCAP-3269-8, June, 1964.

2) G. Helsroni, " Studies of the Connecticut-Yankee Hydraulic Model",

WCAP-2761, June, 1965.

3) L. E. Hochreiter, " Application of the THINC IV Program to PWR Design",

WCAP-8054, October,1973, (proprietary), and WCAP-8195, October,1973 (non-proprietary).

4) P. Saha, M. Ishii and N. Zuber, "An Experimental Investigation of the Thermally Induced Flow Oscillations in Two-Phase Systems", Journal of Heat Transfer, November, 1976, pp. 616-22.

, ATTACHMENT A

. TABLE 1 BEAVER VALLEY UNIT 1 THERMAL AND HYDRAULIC COMPARISON 3 Loop 1 Loop Desion Parameters Operation Isolated Reactor core heat output (MWt) 2,652 1724 Reactor core heat output (108 Btu /hr) 9.051 5884 Heat generated in fuel (%) 97.4

• 97.4 System pressure, nominal (psia) 2,250 2,250 System pressure, minimum steady state (psia) 2,220 2,220 Minimum DNBR at nominal design conditions Typical flow channel 2.26 2.97 Thimble (cold wall) flow channel 1.83 .2.43 Minimum DNBR for design transients >1.30 >1.30 DNB Correlation "R" (W-3 with "R" (W-3 with modified spacer modified spacer factor) factor)

Coolant Flow Total thermal flow rate (108 lbm/hr) 100.8 72.1 Effective flow rate for heat transfer i

(108 lbm/hr) 96.3 68.8 Effective flow area for heat transfer (ft2 ) 41.6 . 41.6 Average velocity along fuel rods (ft/sec) 14.4 10.1 Average mass velocity (10 8 lbm/hr-ft2 ) 2.32 1.66 i

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,- ATTACHMENT A TTLE I (c::ntir.;cd) Paga 6 of 9 3 Loop 1 Loop Coolant Temperatures Operation Isolated Nominal inlet (*F) 542.5 534.4 Average rise in vessel ('F) 67.5 63.2 Average rise in core (*F) 70.3 65.9 Average in core ('F) 579.4 568.7 Average in vessel (*F) 576.2 566.0 Heat Transfer Active heat transfer, surface ama (ft2) 48,600 48,600 Av& rage heat flux (Btu /hr-ft2) 181,400 118,000 Maximum heat flux for normal operation (Btu /hr-ftz) 420,900* 326,700**

Average linear power (kW/ft) 5.20 3.38 Peak linear power for normal operation (kW/ft) 12.l* 9.4**

Peak linear power resulting from overpower transients / operator errors, assuming a maximum overpower of 118". (kW/ft) 18.0 18.0 Peak linear power which would result in -

centerline melt (kW/ft) >18.0 >18.0 Fuel Central Temoerature Peak at linear power for prevention of centerline melt (*F) 4,700 4,700 Pressure drop ***

Across core (psi) 21.3 2.1 11.2 1.1 NOTES:

• This limit is associated with the value of F = 2.32.

• • This limit is associated with the value of F0 = 2.77

• • • Based on best estimate reactor coolant flow hate.

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• - ATTACHMENT A Page 9 of 9 Item III Provide the following infomation relative to the Technical Specifica-tions for two-loop operation.

1. What changes (if any) are required for safety limits, DNB para-meters, and overtemperature delta T setpoint parameters?

Response

The DNB parameters for two-loop operation are included in Section 3.2.5 (Table 3.2-1). The overtemperature and overpower delta T setpoints and reactor trip system instrumentation requirements for two-loop operation are included in Section 3.3.1.1 (Table 3.3-1). The Low Steamline Pressure Safety System interlock and instrumentation for two-loop operation is included in Section 3.3.2.1 (Table 3.3-3).

2. What is the required minimum flow rate for two-loop operation?

Response

The required minimum flow rate for two-loop operation is stated in the Beaver Valley Technical Specifications Section 3.2.5 (Table 3.2-1) which states' the following:

PAPAMETER LIMITS 2 loops in 2 loops in operation operation and loop and isolated 3 loops in stop valves loop stop operation open valves closed RCS Total Flow Rate 265,500 GPM 189,000 GPM 187,800 GPM l

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