ML20196H921

Forwards Response to NRC 981030 RAI Re Proposed TS Change, Reducing RCS Temp & Revising Volumetric Min Flow Rate

ML20196H921
Person / Time
Site:	San Onofre
Issue date:	12/04/1998
From:	Scherer A SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20196H927	List: ML20196H921 ML20196H932
References
TAC-MA2238, TAC-MA2239, NUDOCS 9812090227
Download: ML20196H921 (11)

Text

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. i lb . { SOUTHERN CAtif 0RNIA A. Edwtrd Scherer y EDISON 2rL_,ym l An unsav immiioui.- comyny l ,

! December 04, 1998 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 l

Gentlemen:

Subject:

Docket Nos. 50-361 and 50-362 Response to the NRC Request for Additional Information to Support Proposed Technical Specification Number NPF-10/15-491, Reacter Coolant System (RCS) Temperature Reduction and Volumetric Minimum Flow Rate (TAC Nos. MA2238 and MA2239)

San Onofre Nuclear Generating Station  !

Units.2 and 3 l

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References:

1) LetterfromJamesW.Clifford(NRC)toHaroldB. Ray (SCE), dated October 30, 1998,

Subject:

Request for Additional Information on Change to TCold [ Reactor l Coolant System (RCS) cold leg temperature (T,,u)]

Reduction and RCS Flow Measurement Technical Specification (TAC Nos. MA2238 and MA2239) San Onofre l Nuclear Generating Station Units 2 and 3

2) Letter from Dwight E. Nunn (SCE) to the Document Control Desk (NRC), dated June 19, 1998,

Subject:

ProposedTechnicalSpecificationNumberNPF-10/15-491, RCS Temperature Reduction and Volumetric Minimum Flow Rate, San Onofre Nuclear Generating Station, Units 2 and 3 This letter provides additional information as requested by the U. S. NRC in reference 1. The Southern California Edison responses to the U. S. NRC's '

questions are provided as an enclosure to this letter.

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9812090227 981204 PDR ADOCK 05000361 P PDR P. O. Bos t28 '.;9D002 l San Clemente. CA 92674-0128 949-368-7501 i rax 949--368-7575

Document Control Desk . .

BACKGROUND By reference 2 SCE submitted Amendment Application Numbers 179 to Operating License NPF-10 and 165 to Operating License NPF-15. These amendment applications requested the following changes:

1) A reduction in the minimum primary Reactor Coolant System (RCS) cold leg temperature (T,,u) from 544F to 535F between the 70% and 100% rated thermal power levels.

2) A conversion of the specified RCS minimum flow rate from a " Mass" (i.e., lbm/hr) to a " Volumetric" (gpm) flow basis.

3) Elimination of the maximum RCS flow rate limit.

If you have any questions or would like additional information, please let me know.

Sincerely, Enclosure cc: E. W. Merschoff, Regional Administrator, NRC Region IV J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 2 & 3 J. W. Clifford, NRC Project Manager, San Onofre Units 2 and 3 i

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1 ENCLOSUiG The Southern California Edisons Company (SCE)

Tcold Program Response to NRC Questions i

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l The Southern California Edisons Company (SCE) Tcold Program -

Response to NRC Questiona l

Question 1:

Unlike mass flow rate which is constant in a given loop, the volumetric flow rate is a function of I temperature and will therefore be different for a cold leg than for the corresponding hot leg. The l Bases for Surveillance Requirement 3.4.1.3 allows the use of a heat balance between the primary  ;

and secondary to calculate the flow rate. However, neither the TS nor the Bases for the surveillance requirement state that the flow rate limit applies strictly to the cold leg. Please j modify your submittal (the referenced letter] to include such a statement orjustify your proposed  ;

wording. l Response to Question 1: l The referenced letter is hereby modified by our commitment to add the following to the Bases of

Surveillance Requirement 3.4.1.3

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When the Core Operating Limit Supervisory System (COLSS) is out of service.

Reactor Coolant System (RCS) Volumetric Flow rate is determined manually. An ,

evaluation of the heat balance between primary and secondary plant powers is the l

preferred method. The heat balance involves first determining the RCS mass flow rate and then converting it to volumetric flow rate using the RCS fluid conditions at the discharge of the Reactor Coolant Pumps (RCPs)

Revised pages are provided for your information.

Question 2:

1 On page 3 [of the referenced letter), you stated "for accident analyses that can be affected by 1 elevated flow rates, a flow rate which is conservatively large compared to baseline measured flow l is used " Please provide and justify the flow rate used. In yourjustification, be sure to provide supponing data regarding the maximum flow that can be provided by the pumps.

I Response to Question 2:

The RCS flow rate used in the accident analyses (the accident analyses sensitive to ele .ned flow rates)is 112 % Qdes, where Qdes = Design Volumetric Flow Rate (396,000 gpm). The bases for the selection of this value are as follows:

l 1; At tne time ofinitial startup (beginning of cycle (BOC) 1) for San Onofre Nuclear

Gencrating Station (SONGS) 2 and 3, the measured flow rates were as follows:

l SONGS 2: 107.0 % Qdes SONGS 3: 106.3 % Qdes.

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i The SCE Teold Program - Response to NRC Questions 2 l

2. Since the RCPs are essentially constant volume pumps, it is reasonable to expect the RCS flow rates to remain constant at the BOC 1 values except for the effect of increased system hydraulic resistance due to the effect of steam generator (SG) tube plugging. i Based on this information, the current maximum flow that the pumps can deliver is expected to be less than 107 % Qdes. ,

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3. The flow rate measurement uncertainty is s; 5% Qdes. The methodology and the  !

components of the flow rate uncertainty calculation are as follows:

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The flow is measured in a monthly flow surveillance. The flow measurement uses the calorimetric calculation formula:

RCS Flow Rate = Secondary Calorimetric Power / Change in Enthalpy across the Core L

The flow uncenainty is calculated or verified as part of the safety analysis. Similar to the l flow measurement process the flow measurement uncertainty calculation is based on calorimetric calculation. First, a reference RCS flow is calculated based on the equation shown above.' Then each of the inputs that goes into the equation is perturbed based on .

the uncertainties value (see table 1). This results in a perturbed reference flow rate. This calculation is performed over the entire Limiting Condition for Operation (LCO) range of 1 operating conditions. Finally, the perturbed flow rate and the base flow rate are ,

compared. The ditTerences are determined and statisfcally evaluated to determined the  !

95/95 reference flow rate uncertainty. The current calculated values are provided in  !

table 1, and they are less than 5% Qdes. Should these values change, then the reference l flow uncertainty analysis is updated and the downstream safety analysis is updated.

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The SCE Tcold Program - Response to NRC Questions 3 1

Table i

" Current" Inputs and Results of the Flow Uncertainty Analysis Parameter Uncertainty l

Power

• 2% (20) ,

Pressurizer Pressure 60 psi (20)

Cold Leg Temperature

• 3.4 *F (20)

Hot Leg Temperature

• 3.4 *F (20) l Hot Leg Stratification Bias 1.3 *F Reactor Coolant Pump Differential Pressure 4.14 psi (20)

Reactor Coolant Pump Speed 3.0 RPM (20) l Reference Flow Uncertainty

• 4.95% of design flow (20)

COLSS one-sided volumetric flow uncertainty

• 4.5 % uniform l

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4. Therefore, the current upper volumetric flow rate limit for use in the safety analysis for SONGS 2 and 3 is 112 % Qdes.

l Question 3:

I Please provide the following information regarding the high pressurizer [ pressure] trip value and the main steam safety valve open setpoint used in your analysis of the loss of condenser vacuum event with concurrent single failure. Discuss instrument uncertainties, tolerance, and/or accumulation as applicable. For the main steam safety valves, the technical specification (TS) lift setpoints vary from 1085 psig to 1140 psig. Discuss how this was modeled in your analysis.

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The SCE Tcold Program - Response to NRC Questions 4 Response to Question 3:

Pan 1. High Pressurizer Pressure Trip Value t

l The parameters related to the high pressurizer pressure trip setpoint value that was used in the loss I

of condenser vacuum plus single failure (LOCV+SF) analysis are given below:

Value used in LOCV+SF analysis 2410 psia Instrumentation trip setpoint 2375 psia The analysis value accounts for plant protection system (PPS) cabinet uncertainties and pressure transmitter errors.

For the High Pressurizer Pressure Setpoint, the uncertainties associated with this trip setpoint are l established and documented in SO23-944-C50, Plant Protection System (PPS) Setpoint Calculation.

l The setpoint is established / justified as follows:

Uncertainties taken into consideration are as follows: (all values in PSIA)

1) Analysis setpoint 2410 Normal (includes LOCV+SF) 2434 Harsh II) PPS Cabinet Uncertainties A. Calibration Equipment Error +/- 1.25 B. Calibration Adjustment Error +/- 6.25 (setting tolerance)

C. Bistable Dria + 1.3 84, -1.724 D. Worst Case Normal Error + 3.3, -4.1 (Bistable accuracy)

A statistical combination of these factors give us the following:

Calibration Error +/- 6.25 Periodic Test Error + 6.641 -6.981 l Maximum Operational Error + 7.310, -8.450 I

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The SCE Tcold Program - Response to NRC Questions 5 l III) Process Intrumentation Errors A. Calibration Equipment Errors +/- 1.25 '

B. Calibration Adjustment Errors +/- 6.25 C. Maintenance and Test Equipment (M&TE) Error +/- 7.5 D. Measured Drin +/- 25.0 E. Hysteresis +/- 2.0 F. Ambient Temperature Error +/- 9.0 '

O. Worst Case Normal Temperature Error +/- 9.0 H. Accident Temperature Error +/- 50.0 l i

I. Normal Pressure Uncertainty +/- 2.0 l J. Accident Pressure Uncenainty + 0.0, - 5.0 K. Radiation Error +/- 10.0 L. Seismic Uncertainty +/- 20.0 M. Post Seismic Uncertainty +/- 5.0 N. Insulation Resistance Error + 10.0, -0.0 A statistical combination of these factors give us the following:

Calibration Error +/- 10.0 i Periodic Test Error +/- 29. 41 l Worst Case Normal Error +/- 29.869 Worst Case Normal Error w/ Seismic +/- 35.597 Worst Case Accident Error + 68.371, - 63.371 l IV) Total Loop Uncertainty (TLU) for Normal with Seismic conditions This is determined by a statistical combination of the PPS cabinet Maximum Operating Error and the Process Equipment worst case normal error with the seismic uncertainty.

TLU (Normal w/ Seismic) + 36.340, -37.480 i V) Total Loop Uncertainty (TLU) for Accident conditions This is determined by a statistical combination of the PPS cabinet Maximum Operating Error and the Process Equiprnent worst case accident error.

j TLU (accident) + 68.827, -64.967 i

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The SCE Tcold Program -- Response to NRC Questions 6 I VI) Trip Setpoint and allowable value l

Using the methodology for calculating a setpoint with a single side ofinterest (unidirectional approach to point ofinterest), the random uncenainty can be reduced by a correction factor of 0.839, with the biases then added in aner the correction factor is applied. The setpoint is determined by subtracting the TLU from the analysis setpoint.

Analysis setpoint-Harsh 2434 TLU-Harsh +49.35, -55.49 Maximum trip setpoint-Harsh 2378.5l Analysis Setpoint-Nonnal/Scismic 2410 TLU-Normal / Seismic +30.49, -31.63 Maximum trip setpoint-Normal / Seismic 2378.37 Trip Setpoint with/ margin 2375 i 1

l Part 2. Main Steam Safety Valve Characteristics Nine main steam safety valves (MSSVs) are included on each of the two main steam lines. The lift setting (in psig) for each MSSV is listed in TS Table 3.7.1-2. The listed values are 1085,1092,1099, i 1106,1113,1120,1127,1134, and 1140 psig. The LOCV+SF analysis increases the TS lift settings l to account for +2 % opening tolerance and MSSV opening characteristics as follows:

Step 1. Sina me CESEC code pressure lift setting it in psia, rather than psig,15 psi is added to the TS value to conven the lin setting to psia. The value of the lift setting in psia is multiplied by 1.02 to adjust for +2 % opening tolerance. The resulting adjusted MSSV opening setpoints are 1122, i129.1,1136.3,1143.4,1150.6,1157.7,1164.8,1172.0, and 1178.I psia.

. Step 2. The MSSV characteristics are modeled as indicated in Figure 1. The abscissa of Figure 1 is in units ofpercent of the TS lift setting in psia. From Figure 1 it is seen that each MSSV is assumed to open to 70% of Full Open area at the adjusted MSSV opening setpoint listed in Step 1 above. Afler an accumulation of I %, each MSSV is assumed to open to 100 % of the Full Open area.

In the LOCV+SF analysis, seven of the nine MSSVs in each steam line reached their opening setpoints and five of these seven reached a full open condition.

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. l The SCE Tcold Program - Response to NRC Questions 7 j

Reference:

i Letter from Dwight E. Nunn (SCE) to the Document Control Desk (NRC), dated June 19,1998, i

Subject:

Proposed Technical Specification Number NPF-10/15-491, RCS Temperature Reduction and Volumetric Minimum Flow Rate, San Onofre Nuclear Generating Station, Units 2 and 3 l

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The SCE Tcold Program - Response to NRC Questions s l FIGURE 1 SONGS UNITS 2&3 MSSV OPENING CHARACTERISTICS,2% TOLERANCE 120-100-- < >

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m 1 40-n 20 -

l G l l l 99 100 101 102 103 104 Pressure (Percent of TIS Lift Setpoint) i

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