ML18152A545
| ML18152A545 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna  |
| Issue date: | 04/25/1995 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 95-198, NUDOCS 9505030335 | |
| Download: ML18152A545 (21) | |
Text
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e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 April 25, 1995 United States Nuclear Regulatory Commission Serial No.95-198 Attention: Document Control Desk NA&F/KFF-CGL RO' Washington, D. C. 20555 Docket Nos. 50-338 50-339 50-280 50-281 License Nos. NPF-4 NPF-7 DPR-32 DPR-37 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 SURRY POWER STATION UNITS 1 AND 2 REPORT OF ECCS EVALUATION MODEL CHANGES PURSUANT TO REQUIREMENTS OF 10CFR50.46 Pursuant to 10CFR50.46(a)(3)(ii) Virginia Electric and Power Company is providing information concerning changes to the ECCS Evaluation Models and their application in existing licensing analyses. Information is also provided which quantifies the effect .
of these changes upon reported results for North Anna and Surry Power Stations and demonstrates continued compliance with the acceptance criteria of 10CFR50.46.
Attachment 1 contains excerpted portions of the Westinghouse report describing the changes to the Westinghouse ECCS Evaluation Models which are applicable to North Anna and Surry and have been implemented during the calendar year 1994.
Information regarding the effect of the ECCS Evaluation Model changes upon the reported LOCA analysis of record (AOR) results is provided for the North Anna and Surry Power Stations in Attachments 2 and 3, respectively. To summarize the information in Attachments 2 and 3, the calculated peak cladding temperature (PCT) for the small and large break LOCA analyses for North Anna and Surry are given below. None of these results include significant changes, as defined in 10CFR50.46(a)(3)(i).
North Anna Units 1 and 2 - Small break: 2092°F North Anna Units 1 and 2 - Large break: 2041 °F Surry Units 1 and 2 - Small break: 1812°F Surry Units 1 and 2 - Large break: 2114°F
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' PDR ADOCK 05000280 f
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e We have evaluated these issues and the associated changes in the applicable licensing basis PCT results. These results demonstrate compliance with the requirements of 10CFR50.46(b). No further action is required to demonstrate compliance with 10CFRS0.46 requirements.
If you have further questions or require additional information, please contact us.
Very truly yours, J~~~.i~ 6~
Senior Vice President - Nuclear Attachments:
- 1. Westinghouse Report of ECCS Evaluation Model Changes for 1994 - North Anna Units 1 and 2 and Surry Units 1 and 2
- 2. Effect of ECCS Evaluation Model Changes - North Anna Units 1 and 2
- 3. Effect of ECCS Evaluation Model Changes - Surry Units 1 and 2 cc: U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia 30323 Mr. R. D. McWhorter NRG Senior Resident Inspector North Anna Power Station Mr. M. W. Branch NRG Senior Resident Inspector Surry Power Station
ATTACHMENT 1 WESTINGHOUSE REPORT OF ECCS EVALUATION MODEL CHANGES FOR 1994 NORTH ANNA UNITS 1 AND 2 AND SURRY UNITS 1 AND 2
CODE STREAM IMPRO~
Reference Let'"..er l'ITD-:NR.C-94-4143, "Change in Methodology for Exeeution of BASH Evaluation Model", NJ Liparulo 0!lJ to WT Russell (NRC), May 23, 1994
Background
Revisions were made to the procedures used to interface the various codes that comprise the entire execution stream for performing a large break LOCA analysis with the BASH Evaluation Model.
The previous use of the coupled WREFLOOD/COCO code for calculating containment pressure response, which was then transferred as a boundary condition to the BASH code, has been replaced with direct coupling of the BASH and COCO codes such that the same code used to calculated the
- RCS conditions during reflood, also supplies the boundary conditions for the containment pressure calculation. In conjunction with this, the portion of the WREFLOOD code which calculated the refill phase of the transient has been reprogrammed into a separate, but identical code called REFILL, which is also coupled with COCO.
This methodology revision was made only as a process improvement for conducting analyses and involved no changes to the approved physical models, nor basic solution techniques governing the solutions provided by the individual computer codes. The NRC was advised of the implementation of this methodology on a forward-fit basis via the reference letter.
Affected Evaluation Models 1981 ECCS LBLOCA Evaluation Model with BASH Estimated Effect Due to small perturbations in the boundary conditions resulting from this revised methodology for interfacing the codes, small differences in predicted results were observed. The effects were minor, with no observed bias. Since this methodology is a process improvement which is to be implemented on a forward-fit basis, there are no effects on existing licensing analyses, and any small effects on results will be implicitly accounted for in future analyses.
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BASH: LOOP/CORE INTERFACE CORRECTIONS Bacqround Corrections were made to the logic for interfacing the loop model and BART code model. One correction prevents the possibility of an occasional inconsistency in how the core timestep was limited by the loop timestep. Another corrects the fluid density used in the interface calculation when the inlet flowrate is negative.
Affected Evaluation Models 1981 ECCS LBLOCA Evaluation Model with BASH Estimated Effect
- Results from sensitivity studies for the corrections demonstrated negligible perturbations in the trends of the system parameters with a very minor net effect on peak clad temperature predictions relative to results from the previous version. Since this is an extremely small effect, with no apparent bias, the net effect on existing analyses is estimated to be zero degrees for margin tracking purposes. The change has been implemented on a forward fit basis only and will be incorporated implicitly in any future analyses.
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PELLET POWER RADIAL FLUX DEPRF.SSION ERROR
Background
A coding error (an incorrect sign) was discovered and corrected in a subroutine that calculates radial distribution power factors in the fuel pellet for the LOCBART code.
Affected Evaluation Models 1981 ECCS LBLOCA Evaluation Model with BASH Estimated Effect Sensitivity studies found the error correction to result in less than a +0.1 F effect on predicted peak clad temperature. The net effect on existing analyses is therefore zero degrees for margin tracking purposes, and will be implicitly included in future recalculations.
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IMPROVEMENTS TO FLOODING RATE SMOOTHING
Background
Pan: of the approved .methodolog-y for performing large break LOCA analyses with the BASH Evaluation Model is the requirement that the core inlet flooding rate calculated by the BASH code be linearized in a piece-wise manner to remove oscillations prior to use in the hot channel fuel rod calculation. This operation is termed "smoothing", and guidelines are provided to the analysts describing how to linearize the curve by observing inflections in the overall flooding rate. To facilitate consistency in performing this operation, the logic has been coded into a program named SMUUTIL A new version of the SMUUTH program has been implemented which incorporates improved logic for determining the inflection points gained through experience in utilizing the program for a broad range of plant transients.
Affected Evaluation Models 1981 ECCS LBLOCA Evaluation Model with BASH Estimated Effect There are no changes to the approved evaluation model methodology from this revision. The SMUUTH program merely represents a convenient way of automating the approved methodology and does not explicitly introduce any effects on the results. This revision is being reported only as a change to the code stream used for standard analyses. There are no effects on predicted results from using the new program version.
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B0Il.JNG HEAT TRANSFER CORRELATION ERRORS
Background
This closeiy reiated set of errors deais with how the mixture veiocity is defined for use in various boiling heat transfer regime correlations. The previous definition for mixture velocity did not properly account for drift and slip effects calculated in NOTRUMP. This error particularly affected.
NOTRUMP calculations of heat transfer coefficient when using the Westinghouse Transition Boiling Correlation and the Dougall-Rohsenow Saturated Film Boiling Correlation.
In addition, a minor typographical error was also corrected. in the Westinghouse Transition Boiling Correlation.
This was determined to be a Non-Discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.
Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect ,
Representative plant calculations for this issue resulted in an estimated PCT effect of -6 degrees for affected plants.
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e STEAM.LINE ISOLATION LOGIC ERRORS
Background
a This error consists of two portions: possibie plant specific effect which only appiies to analyses which assumed Main Feedwater Isolation (FWI) to occur on S-signal, and a generic effect applying to all previous analyses.
The possible plant specific effect was the result of incorrect logic which caused the main steam line isolation to occur on the same signal as FWI. Therefore, when the S-signal was chosen through user input to be the appropriate signal for FWI, it also caused the steam line isolation to occur on S-signal.
This is inconsistent with the standard conservative assumption of steam line isolation on Loss of Offsite Power coincident with the earlier Reactor Trip signal.
The generic effect was the result of incorrect logic which always led to the isolation functions occurring at a slightly later time than when the appropriate signal was generated.
This was determined to be a Non-Discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.
Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect Representative plant calculations for this issue resulted in an estimated PCT effect of + 12 °F for the plant specific portion, if applicable, and + 18°F for the generic portion.
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e CORE NODE ZIRC OXIDE INITIAUZATION ERROR
Background
NOTRUMP models two regions for each core node analogous to the two (mixture and vapor) regions in adjoining fluid nodes. During the course of a transient, NOTRUMP tracks region specific quantities for each core node. Erroneous logic caused incorrect initialization of the region specific, fuel cladding zirc oxide thickness at times prior to the actual creation of the relevant region during the core boiloff transient.
This was determined to be a Non-Discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.
Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect Representative plant calculations led to an estimated generic PCT effect of 0°F for this effect.
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e PRESSURE SEARCH CONVERGENCE CRITERIA IN NOTRUMP
Background
The convergence criteria used during the pressure search in NOTRUMP have been found to not be adequately restrictive to ensure a sufficiently accurate value for Fluid Node pressure when conditions approach the boundary between subcooled and saturated in some cases. The resulting effects on predicted pressure were more pronounced at pressures below those normally seen during standard Evaluation Model calculations. The previously hardwired convergence criteria values have been made user input, appropriate values have been determined, and these will be implemented in all future analyses.
This was determined to be a Non-Discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.
Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect The nature of this error led to an estimated generic PCT effect of 0°F for existing analyses.
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e FRICTION VALUE INPUT CORRECTIONS
Background
The SP.A~ES code is used to generate input dech for the small brea..Jc analysis code, NOTRUMP._
An error was found in the code which involved the values assigned to some of the friction factor input. The erroneous values had no impact on transient calculations and were corrected in order to maintain the consistency of the SPADES code with the relevant documentation.
The errors were considered to be discretionary changes as described in Section 4.1.1 of WCAP-13451 and were corrected in accordance with Section 4.1.3 of WCAP-13451.
Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect Representative plant calculations indicate no effect on PCT analyses.
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e AUTOMATIC CONTAINMENT SPRAY ACTUATION DURING SBLOCA
Background
Automatic containment spray actuation during a small break LOCA had not previously been addressed in the Westinghouse small break LOCA evaluation model. The containment pressure transient is not modeled because the small break PCT, is not directly sensitive to this effect. While investigating this issue, however, Westinghouse concluded that containment spray actuation early in the small break transient is possible for a variety of containment types. Containment spray actuation could result in draindown of the RWST prior to conclusion of the small break transient. Switching to cold leg recirculation during the transient may reduce or briefly interrupt the modeled ECCS injection flow in some plants and elevate the enthalpy of ECCS injection water. Furthermore, an alternate single failure scenario could result in earlier draindown for the RWST and subsequent switchover to cold leg recirculation.
Future small break LOCA analyses will explicitly consider these issues.
Affected Evaluation Models 1975 SBLOCA Evaluation Model (WFLASH) 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect Plant specific evaluations of affected plants currently indicate no PCT effect due to SI interruption or reduction following switchover to cold leg recirculation. A generic evaluation for the increase in ECCS enthalpy with an alternate single failure has yielded.a PCT penalty of 20°F for some plants.
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SBLOCTA REVISIONS AND AXIAL NODALIZATION ERRORS Reference Letter NTD-NRC-94-4343, "Interim Report of an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2) - Closeout 94-002", NJ Liparulo , November 15, 1994
Background
Westinghouse has completed an evaluation of issues concerning the SBLOCTA code which is a part of both the NOTRUMP and WFLASH SBLOCA ECCS Evaluation Models. The potential issue originally identified was a deficiency in the amount of detail used for the axial nodalization of the fuel rod, as it affected the solution of the channel fluid equations. Further investigation identified several additional related issues associated with nodalization and the overall solution of the fluid conservation equations which have subsequently been corrected. As a separate, but related issue, a revised model for calculating transient fuel rod internal pressure was implemented in the SBLOCTA code. The NRC was informed of these modeling changes, which were summarized in the closeout notification of the reference.
Affected Evaluation Models 1985 SBLOCA Evaluation Model (NOTRUMP) 1975 SBLOCA Evaluation Model (WFLASH)
Estimated Effect Since all of the issues relate to portions of the SBLOCTA code and/or its associated input methodology, they were reported as a single closely-related group of changes. Evaluations were performed for all plants and the results reported to the utilities. R~vised SBLOCA Margin Utilization Summary tables were transmitted containing a compilation of the net effect as item "Axial Nodalization, RIP Model Revision and SBLOCTA Error Corrections", along with sufficient information for reporting, if necessary.
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e SAFETY INJECTION IN THE BROKEN LOOP Reference WCAP-10054-P, Addendum 2, "Addendum to the Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code: Safety Injection into the Broken Loop and COSI Condensation Model," August, 1994.
Background
The referenced topical report presents a change to the Westinghouse SBLOCA methodology dealing with ECCS flows in the broken loop. It also presents a revised condensation model that will be used on the safety injection jet in future analyses.
This change is being implemented on a forward fit basis prior to formal approval in accordance with Section 4.1.3 of WCAP-13451.
Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)
Estimated Effect This change* has been shown to typically produce PCT benefits in studies presented in the reference.
Since it is being implemented on a forward fit basis, a net PCT impact of 0°F is being assessed against existing analyses.
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ATTACHMENT 2 EFFECT OF WESTINGHOUSE ECCS EVALUATION MODEL CHANGES NORTH ANNA UNITS 1 AND 2
e Effect of Westinghouse ECCS Evaluation_ Model Changes - North Anna The information provided herein is applicable to North Anna Power Station Units 1 and 2. It is based upon reports from Westinghouse Electric Corporation for issues involving the ECCS evaluation models and plant-specific application of the models in the existing analyses. Peak cladding temperature (PCT) values and margin allocations represent issues for which permanent resolutions have been implemented.
Section A presents the detailed assessment for small break LOCA. The large break LOCA details are given in Section B.
Section A - Small Break LOCA Margin Utilization - North Anna Units 1 and 2 A. PCT for Analysis of Record 1880°F (1)
B. Prior PCT Assessments Allocated to AOR +200°F
- 1. Safety Injection in the Broken Loop (NOTRUMP) 0°F (2)
- 2. SBLOCA Limiting Time in Life - Zirc/Water Oxidation +81°F (3)
- 3. SBLOCTA Revisions and Axial Nodization Errors +119°F (4)
SBLOCA Augmented PCT for AOR 2080°F C. PCT Assessments for 10CFR50.46(a)(3)(i) Accumulation 24°F
- 1. NOTRUMP Boiling Heat Transfer Correlation Errors {1} {2} -6°F
- 2. NOTRUMP Steam Line Isolation Logic Errors {1} {2} +18°F
- 3. Automatic Containment Spray Actuation {1} {2} {3} 0°F SBLOCA Licensing Basis PCT (AOR PCT+ PCT Assessments) 2092°F Section B - Large Break LOCA Margin Utilization - North Anna Units 1 and 2 A. PCT for Analysis of Record 2066°F (5)
B. Prior PCT Assessments Allocated to AOR -19°F
- 1. Structural Metal Heat Modelling (WREFLOOD) -25°F (2)
- 2. LBLOCA/Seismic SG Tube Collapse +6°F (6)
LBLOCA Augmented PCT for AOR 2047°F C. PCT Assessments for 10CFR50.46(a)(3)(i) Accumulation 6°F
- 1. Vessel & SG Calculation Errors in LUCIFER -6°F (3)
- 2. LBLOCA Rod Internal Pressure Issues 0°F (3)
LBLOCA Licensing Basis PCT (AOR PCT+ PCT Assessments) 2041 °F Notes { } and References ( ) on the following page 2-1
Effect of Errors/Changes in Application of ECCS Evaluation Models -
North Anna Units 1 and 2 Notes:
{1} The current report is the initial quantification of effects for this issue.
{2} Refer to the Report of Westinghouse ECCS Evaluation Model Changes for 1994 provided in Attachment 1.
{3} This item was evaluated using plant-specific input with Westinghouse analytical guidelines.
References:
(1) North Anna Station Safety Evaluation, 94-SE-OT-044, "North Anna Power Station Units 1 and 2 - Safety Evaluation for Revised Small Break Loss of Coolant Analysis (SBLOCA)", July 14, 1994.
(2) Letter from W. L. Stewart (Va. Electric & Power Co.) to NRC, "Report of ECCS Evaluation Model Changes and 30-Day Report Per Requirements of 10CFR50.46-North Anna Power Station Units 1 and 2, North Anna Power Station Units 1 and 2," Serial No. 93-1828, November 9, 1993.
(3) Letter from J. P. O'Hanlon (VEPCO) to Document Control Desk (USNRC),
"Virginia Electric and Power Company, North Anna Power Station Units 1 and 2, Report of ECcs, Evaluation Model Changes and 30-Day Report Pursuant to 10CFR50.46 Requirements," Serial No.94-436, July 25, 1994.
(4) Letter from J. P. O'Hanlon (VEPCO) to Document Control Desk (USNRC),
"Virginia Electric and Power Company, North Anna Power Station Units 1 and 2, 30-Day Report of ECCS Evaluation Model Changes Per Requirements of 10CFR50.46," Serial No. 94-436A, February 7, 1995.
(5) Letter from W. L. Stewart (Va. Electric & Power Co.) to NRC, "North Anna Power Station Units 1 and 2, Proposed Technical Specifications Changes -
Implementation of ZIRLO Cladding," Serial No.93-614, October 4, 1993.
(6) Letter from W. L. Stewart (VEPCO) to Document Control Desk (USNRC), "Virginia Electric and Power Company, Report of ECCS Evaluation Model Changes and 30-Day Report Per Requirements of 10CFR50.46, North Anna Power Station Units 1 and 2," Serial No. 93-182A, July 16, 1993.
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e ATTACHMENT 3 EFFECT OF WESTINGHOUSE ECCS EVALUATION MODEL CHANGES SURRY UNITS 1 AND 2
e e Effect of Westinghouse ECCS Evaluation Model Changes - Surry The information provided herein is applicable to Surry Power Station Units 1 and 2. It is based upon reports from Westinghouse Electric Corporation for issues involving the ECCS evaluation models and plant-specific application of the models in the existing analyses. Peak cladding temperature (PCT) values and margin allocations represent issues for which permanent resolutions have been implemented. Section A presents the detailed assessment for small break LOCA. The large break LOCA details are given in Section B.
Section A - Small Break LOCA Margin Utilization - Surry Units 1 and 2 A. PCT for Analysis of Record 1852°F (1)
B. Prior PCT Assessments Allocated to AOR -2°F
- 1. Safety Injection in the Broken Loop (NOTRUMP) 0°F (2)
- 2. NOTRUMP Drift Flux Flow Regime Map Errors -13°F (2)
- 3. Vessel & SG Calculation Errors in LUCIFER -16°F (3)
- 4. SBLOCA Limiting Time in Life - Zirc/Water Oxidation +15°F (3)
- 5. NOTRUMP Boiling Heat Transfer Correlation Errors -6°F (4)
- 6. NOTRUMP Steam Line Isolation Logic Errors +18°F (4)
SBLOCA Augmented PCT for AOR 1850°F C. PCT Assessments for 10CFR50.46(a}(3)(i) Accumulation 38°F
- 1. SBLOCTA Revisions and Axial Nodalization Errors {1} {2} {3} -38°F
- 2. Automatic Containment Spray Actuation {1} {2} {4} 0°F SBLOCA Licensing Basis PCT (AOR PCT+ PCT Assessments) 1812°F Section B - Large Break LOCA Margin Utilization - Surry Units 1 and 2 A. PCT for Analysis of Record 2120°F(5)
B. Prior PCT Assessments Allocated to AOR (None) 0°F LBLOCA Augmented PCT for AOR 2120°F C. PCT Assessments for 10CFR50.46(a)(3)(i) Accumulation 6°F
- 1. Vessel & SG Calculation Errors in LUCIFER -6°F(3)
- 2. LBLOCA Rod Internal Pressure Issues 0°F(3)
LBLOCA Licensing Basis PCT (AOR PCT+ PCT Assessments) 2114°F Notes { } and References ( ) on the following page 3-1
Effect of Errors/Changes in Application of ECCS Evaluation Models -
Surry Units 1 and 2 Notes:
{1} The current report is the initial quantification of effects for this issue.
{2} Refer to the Report of Westinghouse ECCS Evaluation Model Changes for 1994 provided in Attachment 1.
{3} The sensitivity study result includes the effects of the following items reported in Reference (3):
Hot Assembly Average Rod Burst Effects and Revised Burst Strain Limit Model.
{4} This item was evaluated using plant-specific input with Westinghouse analytical guidelines.
References:
(1) Letter from W. L. Stewart (Va. Electric & Power Co.) to NRC, "Surry Power Station Units 1 and 2 - Proposed Technical Specifications Changes - F~H Increase/Statistical DNBR Methodology," Serial No.91-374, July 8, 1991.
(2) Letter from W. L. Stewart (Va. Electric & Power Co.) to NRC, "Report of ECCS Evaluation Model Changes and 30-Day Report Per Requirements of 10CFR50.46-Surry Power Station Units 1 and 2, North Anna Power Station Units 1 and 2," Serial No. 93-182B, November 9, 1993.
(3) Letter from W. L. Stewart (VEPCO) to Document Control Desk (USN RC), "Virginia Electric and Power Company, Surry Power Station Units 1 and 2, 30-Day Report of ECCS Evaluation Model Changes Per Requirements of 10CFR50.46," Serial No.94-254, April 27, 1994.
(4) Letter from W. L. Stewart (VEPCO) to Document Control Desk (USN RC), "Virginia Electric and Power Company, Surry Power Station Units 1 and 2, 30-Day Report of ECCS Evaluation Model Changes Per Requirements of 10CFR50.46," Serial No. 94-254A, September 26, 1994.
(5) "Surry Power Station Units 1 and 2 - Safety Evaluation for Revised Large Break LOCA Analysis," 10CFR50.59 Safety Evaluation 94-082, March 28, 1994.
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