ML20082C106
| ML20082C106 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 07/08/1991 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9107180035 | |
| Download: ML20082C106 (11) | |
Text
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$O2$N..,. cm July 8, 1991 e m u" U.
S.
Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555
Subject:
Beaver Valley Power Station, Unit No. I and No. 2 BV-1 Docket No. 50-334, Licenso No. DPR-66 BV-2 Docket No. 50-412, License No. NPF-73 10 CPR 50.46 Report of Changes or Errors in ECCS Evaluation Models Transmitted herewith is the annual report of changes or errors in ECCS evaluation models which is submitted in accordance with the requirements of 10 CFR 50.46.
This report describes the nature of each change or error and its estimated effect on the limiting ECCS analysis.
The following attachments provide the required information:
ATTACllMENT A
provides a
list of references used in this report.
Each reference has been submitted to the NRC.
ATTACllMENT 11 provides a
plant specific description of ECCS evaluation model changes or errors for Beaver Valley Power Station Unit 1.
This information was provided by Westinghouse to the NRC on a generic basis in references 2 and 3.
Plant specific estimates of the effect of these changes or errors on peak clad temperature (PCT) is also provided.
ATTACHMENT C
provides information similar in content to Attachment B for Beaver Valley Power Station Unit 2.
No additional changes or errors have been identified during this reporting period.
- However, information which has recently been received from Westinghouse is being evaluated and may necessitate further reporting in the near future.
Sincerely,
.b e
Vice President Nuclear Group cc:
Mr.
J.
Beall, Sr. Resident Inspector Mr.
T.
T.
Martin, NRC Region I Administrator Mr. A.
W. DeAgazio, Project Manager Mr.
M.
L.
Bowling (VEPCO) 9107D3OO35 91070c#
(DR ADOCK 0500G334 PDR
]
Id
ATTACHMENT A-REFERENCES 1.
" Emergency Core Cooling Systems; Revisions to Acceptance Criteria,"
Federal
- Register, Vol. 53, No. 180, pp. 35996-36005, Dated September 16, 1988.
2.
NS-NRC-89-3463,-
"10 CFR 50.46 Annual-Notification for 1989 of Modifications in the Westinghouse ECCS Evaluation Models," Letter from W.J.
Johnson (Westinghouse) to T.E.
Murley (NRC), Dated October 5, 1989.
3.
NS-NRC-89-3464,
" Correction of Errors and Modifications to the NOTRUMP Code in the Westinghouse Small Break LOCA ECCS Evaluation Model Which Are Potenth 'ly Significunt,"
Letter from W.J.
Johnson (Westinghouse) to f.E Murley (NRC),
Dated October 5, 1989.
A Nodal Transient Small Break and General Network 4.
"NOTRUMP Code,"
WCAP-10079-P-A (Proprietary),
- Meyer, P.E.,
et.,
al.,
August 1985.
5.
Beaver Valley Unit 1
Updated Final Safety Analyses
- Report, Revision 8.
6.
Beavet Valley Unit 2
Updated Final Safety Analysis
- Report, Revision 2.
______.-_-_____--_mm-.._.
ATTACWENT B EFFECT OF WESTINGHOUSE ECCS EVALUATION WODEL WBIFICATIONS ON THE LOCA ANALYSIS RESULTS FOUW IN CHAPTER 14 0F THE BEAVER VALLEY UNIT 1 UPDATED FINAL SAFETY ANALYSIS REPORT The October 17, 1988 revision to 10CFR50.46 required applicants and holders of operating licenses or construction permits to notify the Nuclear Regulatory Comistion (NRC) of errors and changes in the ECCS Evaluation Models on an annual basis, when the errors and changes are not significant. Reference 1 defines a significant error or change as one which results in a calculated poi.k fuel cladding temperature different by more than 50*F from the temperature calculated for the limiting transient using the last acceptable model, or is a cumulation of changes and errors such that the sum of the absolute magnitudes of the respective temperature changes is greater than 50'F.
In References 2 and 3, information regarding modifications to the Westinghouse large break and small break LOCA ECCS Evaluation Models was submitted to the NRC.
The following presents an assessment of the effect of the modifications to the Westinghouse ECCS Evaluation Models on the loss of coolant accident (LOCA) analysis results found in Chapter 14 of the Beaver Valley Unit 1 Updated Final Safety Analysis Report (reference 5).
LARGE BREAK LOCA The large break LOCA enalyses for Beaver Valley Unit 1 were examined to assess the effect of the applicable modifications to the Westinghouse large break LOCA ECCS Evaluation Model on peak cladding toccarature (PCT) resuits reported in Chapter 14 of the UFSAR< The large break LOCA analyses results were calculated psing the 1981 version of the Westinghouse large break LOCA ECCS Evaluation Model incorporating the BASH analysis technology.
The analysis assumed the following information important to the large break LOCA analyses; Licensed Core Power 2652 MW Core Total Peaking Factor, FQ 2.4 Steam Generator Tube Plugging 10%
Fuel Type 17
- 17 Standard For Becver~ Valley Unit 1 the lietting break resulted from the double ended guillotine rupture of the cold leg piping with a discharge coefficient of CD = 0.4 for the Maximum Safeguards case. The calculated peak cladding temperature wam 1918'F.
The following modifications to the Westinghouse ECCL Evaluation Models discussed in Reference 2 would affect the large break LOCA analysis results found in Chapter 14 of the Beaver Valley Unit 1 Updated Final Safety Analysis Report.
84870 to
Several isprovements were made to the BASH computer code to treat special analysis cases which are related to the tracking of fluid interfaces;
- 1) A modification, to prevent the code from aborting, was made to the heat transfer model for the special situation when the quench front region moves to the bottom the the BASH core channel.
The quench heat supplied to the fluid node below the bottom of the active fuel was set to zero.
- 2) A modification, to prevent the code from aborting, was made to allow negative initial movement of the liquid /two phass and liquid-vapor interfaces. The coding these areas was generalized to prevent mass imbalance in the special case where the liquid /two phase interface reaches the bottom of the BASH core channel.
- 3) Modifications, to prevent the code from aborting, were made to increase the dimensions of certain arrays for special applications.
- 4) A modification was made to write additional variables to the tape of information to be provided to LOCBART.
- 5) Ty: w aphical errors in the coding of soms convective heat transfer-terms were corrected, but the corrections have no effect on the 2 ASH analysis results since the related terms are always set equal to zero.
- 6) A adification was made to the BASH coding to reset the cold leg l
conditions, in a conservative manner, wherr the accumulators empty.
t The BASH model is initialized at the bottom of core recovery with the intact cold legs, loner plenum full of liquid. Flow into the downconer then equals the accumulator flow.
The modification removed most of the intact cold leg water at the accumulator empty time by.
resetting the intact cold leg conditions to a high quality two phase mixture.
In a typical BASH calculation, the downconer is nearly full when-the accumulators emptied. The~ delay time, prior to the intact cold-leg.
t water reaching saturation, is sufficient'to allow the downconer to fill from the addition of safety. injection fluid before the water in the cold legs reaches saturation. When the intact cold leg water reached saturation it'merely flowed out of the break. The cold leg water therefore, did not affect the reflood transient.
However,' in a special case, a substantial time was required to fill the douacomer after the accumulators emptied. The fluid in the intact cold lege reached saturation before the downcomer filled,twhich artific' ally perturbed the transient response by incorrectly altering the downcomer fluid conditions causing the code-to abort.
For Beaver Valley Unit 1 LOCA analysis results could be affected by the-modifications specified in items 1, 2, 3, 4, 5, and 6 above. While there is-no adverse effect on the PCT calculation for the majority of the changes which apply to Beaver Valley Unit 1 discussed above, a conservative estimate of-10*F will be assessed and tracked for used in determining the available margin To the limits of 10CFR50.46.
?
90870.34 -
As discussed above, modifications to the Westinghouse large break LOCA ECCS-Evaluation Model could affect the result by altering the PCT.
A.
Analysis calculated result 1918'F B.
Modifications to Westinghouse ECCS Evaluation Model 1
+ 10'F I
ECCS Evaluation Model Modifications Resultant PCT TFlB'F l
SMALL BREAK LOCA i
The small break LOCA analyses for Beaver Valley Unit I were also examined to i
assess the effect of the applicable modifications to the Westinghouse ECCS Evaluation Models on peak ciadding temperature (PCT) results reported in Chapter 14 of the UFSAR. The small break LOCA analyses results were calculated using the 1985 version of the Westinghouse small break LOCA ECCS Evaluation Model incorporating the NOTRUMP analysis technology.
The analysis j
assumed the following information important to the small break LOCA analyses-Licensed Core Power 2652 MW Core Total Peaking Factor, FQ 2.4 Steam Generator Tube Plugging 10%
i Fuel Type 17
- 17 Standard For Beaver Valley Unit 1, the limiting size small break resulted from a 3-inch equivalent diameter break in tim cold leg.
The calculated peak cladding temperature was 1802*F.
j The following modifications to the Westinghouse ECCS Evaluation Models i
discussed in Reference 2 would affect the small break LOCA analysis results found in Chapter 14 of the Beaver Valley Unit 1 Updated Final Safety Analysis Report.
The Westinghouse small break LOCA ECCS Evaluation Model analyses for Beaver i
Valley Unit 1 were performed with a version of the NOTRUMP computer which did t
not incorporate the following potentially significant modifications noted in-Reference 2;-
- 1) The modification.to preclude changing the region designation (upper, lower) for a node in a stack which does not contain the sixture-vapor
}
interface was not incorporated in the small break LOCA analyses for Beaver Valley Unit 1.
The purpose of the modification was to enhance trackisp ef the mixture-vapor interface in a stacked-series ~of fluid nodes and to preclude'a node in a stack, which does not contain the-t sixture-vepor interface, from changing the region designation.
The update does not affect the fluid conditions in the nodes-representing the reactor coolant system,.only the designation of the region of-the node.
The region designation does not typically affect tho calculations, except for the nodes representing the core fluid volume t
(corenodes).
In core nodes which are designated.as containing vapor-regions, the use of the steam cooling heat transfer correlation-is forced on the calculation in compliance with the requirement 'of-Appendix K to 10CFR50, even if the node conditions would indicate i
l otherwise. This modification could affect the heat transfer
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904*0 10 t.
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calculation if the region designation was improperly' reflected, but
~}
is expected to result in a small decrease in the PC l
if the correction were taken into account.
i 2)
The modification to correct typographical errors in-the equations j
i which calculate the heat transfer rate derivatives for subcooled, saturated, and superheated natural convection conditions for the the 4
upper region of interior fluid nodes were not included in the small break LOCA analyses for Beaver Valley Unit 1.
The heat transfer rate
'l derivatives for subcooled,- saturated, and superheated natural i
convection conditions for the the upper region of interior fluid nodes i
used of the lower region heat transfer area instead of the upper-region heat transfer area, which could in rare instances, affect the i
amount of heat that could be transferred to the fluid.
i Incorporating the modification into the small-break LOCA analyses could result in an l
increase in the PCT of 36.7'F.
l
- 3) The modification to correct typographical error in equations which
-i calculate the derivatives of-the natural convection mode of heat transfer in the subroutine HEAT were not included in the small tr.eak LOCA analyses for Beaver Valley Unit 1.
i However, incorporating the correction into the analyses would have no effect on the analysis results.
The modification to correct a typographical error in an equation which 4) calculates the internal energy for nodes _ associated with the reactor i
coolant pump model when the associated reactor coolant pump flow links are found to be in critical flow was not included in the small break LOCA analyses for Beaver Valley Unit 1.
Since the small break LOCA i
Evaluation Model calculations did not encounter critical flow.in the reactor coolant pump flow links, including this modification would
[
have no effect on the analysis results.
Modifications were made to the small break-LOCTA-IV computer code used in the small break LOCA ECCS Evaluation Model.
modifications could, at most, result in a very small benefit the effect ofSinc modification to the small break LOCTA-IV code modifications do not assessed or tracked.
i.
t The effect of-the potentially significant ECCS Evaluation Model modifications on the small break LOCA analyses for Beaver Valley Unit I could result in a penalty in the peak cladding temperature calculation if taken into account.
For conservatism in estimat<ng the available margin, a peak cladding temperature penalty of approximately 37'F should be added to the analysis i
available margin to the limits of 10CFR50.46.-cal:ulations ae'a result o j
As' discussed above, modifications to the Westinghouse small break LOCA ECCS altering the: PCT. Evaluation Model could affect the small break LOCA analysis res i.
b A.
Analysis calculated result
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va a o N os a n
90$ft te
ATTACIDGtNT C l
l EFFECT OF WESTINGHOUSE ECCS EVALUATION N0 DEL NESIFICATIGIS ON THE LOCA ANALYSIS RESULTS Foule IN CHAPTER-15 Cf THE o
BEAVEA VALLEY UNIT 2 UPDATED FINAL SAFETY ANALYSIS REPORT The October 17, 1988 revision to 10CFR50.46 required applicants and holders of operating licenses or construction permits to notify the Nuclear Regulatory Connission (NRC) of errors and changes in the ECCS Evaluation Models on an annual basis, when the errors and chanps are not significant.
Reference 1 defines a significant error or change as one which results in a calculated peak fuel cladding temperature different by more than 50*F from the temperature calculated for the limiting transient _ using the_.last acceptable model, or is a cumulation of changes and errors such that the sua of the-absolute magnitudes of the respective temperature changes is greater than 50'F.
In References 2 and 3, information regarding modifications to the Westinghouse large break and small break LOCA ECCS Evaluation Models was submitted to the NRC.
The following presents an assessment of the effect of the modifications to the Westinghouse ECCS Evaluation Models on the loss-of-coolant accident (LOCA) analysis results found in Chapter 15 of the Beaver Valley Unit 2 Updated Final Safety Analysis Report (reference 6).
LARGE BREAK LOCA The large break LOCA analyses for Beaver Valley Unit 2 were examined to assess the effect of the applicable modifications to the Westinghouse large break LOCA ECCS Evaluation Model on peak cladding temperature (PCT) results reported in Chapter 15 of the UFSAR.
The large break LOCA analyses results were calculated using the 1981 version of the Westinghouse large hreak LOCA ECCS Evaluation Model incorporating the BART analysis technology.
The analysis assumed the following information important to the large break LOCA analyses; Licensed Core Power 2652 NW-Core Total Peaking Factor, FQ 2.32 Steam Generator Tube Plugging 55 Fuel Type 17
- 17 Standard For Beaver Valley Unit.2, the limiting break resulted from the double ended-guillotine rupture of the cold leg pip'ng with a discharge coefficient of-CD = 0.4 for the Minimum Safeguards case. No Mrximum Safeguards case was performed in tMa analysis.
he calculated peak: cladding temperature was 2120'F.
'The following modifications to the Westinghouse (CCS Evaluation Models discussed in Reference 2 would affect the large break-LOCA analysis results-found in Chapter 15 of the Beaver Valley Unii: 2 Updated Final Safety innalysis Report; l.
OMFG 98
_ _ _... _. _ _ _ ~ _ - _ _.
I i
Modificattens to the WREFLOOD code in the 1981 version of the Westinghouse ECCS Evaluetten Wodel incorporating the 8 ART analysis technology-were made to delay danncomer overfilling. The delay corresponds te backfilling of the intact cold legs.
Data from tests simulating cold leg injection during the post-large break LOCA reflood phase which have adequate safety injection flow to condense all of the available steam flow show a significant amount of subcooled liquid to be present in the cold leg pipe test section.
This situation corresponds to the so-called maximum safety 1
injection scenario of ECCS Evaluation Model analyses, i
r ine Beaver Valley Unit 2 LOCA analyses performed with the Westinghouse 1981 large break LOCA ECCS Evaluation Model incorporating the BART analysis technology are not affected by the WREFLOOD code modifications l
since the maximum safeguards safety injection flow assumption case is'not applicabis.
As discussed above, modifications to the Westinghouse large break LOCA ECCS f
Evaluation Wodel do not affect the PCT result.
A.
Analysis calculated result 2120*F B.
Modifications to Westinghouse ECCS Evaluation Model
+
0*F ECCS Evaluation Model Modifications Resultant PCT-
"7175*F
,j SMALL BREAK LOCA The small break LOCA analyses for Beaver Valley Unit 2 were also examined to assess the effect of the applicable modifications to the Westinghouse ECCS
-t i
Evaluation Models on peak cladding-temperature (PCT) results reported;in Chapter 15 of the UFSAR.
The small breat LOCA analyses results were calculated using the 1985 version of the Westinghouse small break LOCA ECCS i
Evaluation Model incorporating the NOTRUMP analysis technology, 'The analysis 1
i assumed the following information important to the smal.1 break LOCA analyses; j
Licensed Core Power 2652 W i
Core Total Peaking Factor, FQ 2.32 i
Steam Generator Tube Plugging 5.345 Fuel Type 17
- 17 Standard.
-)
For Beaver Valley Unit 2, the limiting size small break resulted from a s
4-inch equivalent diameter break in the cold leg.: The calculated peak cladding tempeee8mre was 1399'F.
l The following seitfications to the Westinghouse.ECCS Evaluation Modela -
discussed in Reftrence 2 would affect the small break LOCA analysis results found in Chapter 15 of the Beaver Valley Unit 2 Updated Final Safety Analysis Report.
~
The Westinghouse small break LOCA ECCS Evaluation Model analysas for Beaver t
Valley Unit 2 were performed with a version of the NOTRUMP computer which did l
not incorporate the following potentially significant modifications noted in Reference 2;-
l 1
see m es
e 1
- 1) The modification to preclude changing the region designation (upper, lower) for a node in a stack which does not contain the mixture-vapor interface was not incorporated in~the small break LOCA analyses for Beaver Valley Unit 2.
The purpose of the modification was to enhance tracking of the sixture-vapor interface in a stacked series of fluid nodes and to preclude a node in a stack, which does not contain the mixture-vapor interface, from changing the region designation.
The update does not affect the fluid conditions in the nodes representing the reactor coolant system, only the designation of the region of the node. The re calculations,gion designation does not typically affect the 4
except for the nodes representing the core fluid volume (core nodes).
In core nodes which are designated as containing vapor regions, the use of the steam cooling heat transfer correlation is forced on the calculation in compliance with the requirements of Appendix K to 10CFR50, even if the node conditions would indicate otherwise.
This modification could affect the heat transfer calculation if the region designation was improperly reflected, but is expected to result in a small decrease in the PCT if the correction were taken into account.
- 2) The modification to correct typographical errors in the equations which calculate the heat transfer rate derivatives for subcooled.
saturated, and superheated natural convection conditions for the the upper region of interior fluid nodes were not included in the small.
break LOCA analyses for Beaver Valley Unit 2.
The heat transfer rate -
derivatives for subcooled, saturated, and superheated natural-convection conditions for the the upper region of interior fluid nodes used of the lower region heat transfer area instead of the upper-region heat transfer area, which could in rare instances, affect the amount of heat that could be transferred to the fluid. -Incorporating the modification into the small break LOCA analyses could result in an increase in the PCT of 36.7'F.
- 3) The modification to correct typographical errors in equations which calculate the derivatives of the natural convection mode of heat transfer in the subroutine HEAT were not included in the small break LOCA analyses for. Beaver Valley Unit 2.
However. incorporating the correction into the analyses would have no effect on the analysis results.
- 4) The modification to correct a typographical error in an equation which calculates the internal energy for nodes associated with:the reactor coolavt pump model when the associated reactor coolant pump flow links-4 are found to be in critical flow was not included in the small break.
LOCA analyses for Beaver Valley Unit 2.
Since the small~ break LOCA Evaluation Model calculations did not encounter critical flow in the-reactor coolant pump flow links, including this modification would-have no effect on the analysis results.
- 5) The modification to correct an error in the implementation of' equation 5-33 of reference 4 was not included in.the_small break LOCA analyses for Beaver Valley Unit 2.
Equation 5-33 describes the calculation of-the flow link friction parameter c, for single phase flow in a-non j
critical flow link k.
In the erroRecus implementation, equation 5-33 i
GAS?$.te i
I
-__w.,_.___
_-.__-,--._,--,_.2-.._,-_,.m.,-
1 was replaced by equation 5-34 which is used for all flow conditions.
This modification was expected to have only a small beneficial effect on the analysis. However, an analysis calculation was performed for a three-loop plant to quantify the effect and a lar decrease in the peak cladding temperature of 217'ger than expected F resulted. Larger than expected peak cladding temperature sensitivities, in some instances, have been observed when analyses to support safety evaluations of the effect of plant design changes under 10CFR50.46 were performed using the NOTRUMP computer code. The unexpected sensitivity results are under investigation at Westinghouse and may be due to the artificial restrictions on loop seal steam venting placed on the model for conservatism.
Evaluation of the effect of this change will be examined as part of the investigation of the larger than expected sensitivity results.
- 6) The modification made to prevent code aborts resulting from implementation of a new FORTRAN compiler on the Westinghouse CRAY computer system was not included in the small break LOCA analyses for Beaver Valley Unit 2.
Due to the different treatments of the precision of numbers between the FORTRAN concilors, the subtraction of t
two large, but close numbers resulted in zero.
The zero value was used in the der.ominator of a derivative equation, which resulted in the code aborts.
Implementing this modification for cases which did not abort has the potential to result in an increase in the PCT of approximately 4.B'F.
- 7) The modification to properly call some doubly dimensioned variables in subroutines INIT and TRANSNT was not included in the small break LOCA analyses for Beaver Valley Unit 2.
However, all of the doubly dimensioned variables used a 1 as the second dimension in all of the erroneous calls, and therefore this modification would have no effect on the PCT.
- 8) The modification to correct an error in implementing equations L-28, L-52 and L-29, L-53 of reference 4 was not included in the small break LOCA analyses for Beaver Valley Unit 2.
Thetwopgirsofequations respectivelydescribethepartialgerivativesofF with respect to pressure and specific enthalpy. F is an interpolation parameter that is defined by equations L-27, L-51 of reference 4.
This modification,could affect the small break LOCA calculation, but is expected to result.in a decrease in the PCT if the correction were taken into account through a new analysis.
Modifications were also made to the small break LOCTA-IV computer code used in the small break LOCA ECCS Evaluation Model. Since the small break LOCTA-IV code modifications could, at most, result in a very small benefit the effect of modification to the small break LOCTA-IV code modifications do not need to be assessed or tracked.
The effect of the potentially significant ECCS Evaluation Modal modifications on the small break LOCA analyses for Beaver Valley Unit 2 could result in a penalty in the peak cladding temperature calculation if taken into account.
For conservatism in estimating the available margin, a peak cladding 88470 84
temperature penalty of approximately 420F should be added-to the analysis c41culations as a result of ECCS Evaluition Model changes when determining the available margin to the limits of 10CFR50.46.
As discussed above, modifications to the Westinghouse small break LOCA ECCS Evaluation Model could affect the small break LOCA analysis results by altering the PCT.
A.
Analysis calculated result 1399'F B.
Modifications to Westinghouse ECCS Evaluation Modal
+ 42*F ECCS Evaluation Model Modifications Pesultant PCT
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