ML20059B680
| ML20059B680 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 10/22/1993 |
| From: | Schnell D UNION ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ULNRC-2892, NUDOCS 9310290054 | |
| Download: ML20059B680 (11) | |
Text
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Pm10ther Bu la9 St. Ioue Maoun Gl!6 314 b54 M$il i
Donald F. Schnerl Etrac1,1tu:
Sen r Vce PresideM nc~,
E3 October 22, ]993 U.S. Nuclear Regulatory Commission Attn:
Document Control Desk i
Mail Station P1-137 Washington, DC 20555 Gentlemen:
ULNRC-2892-DOCKET NUMBER 50-483 CALLAWAY PLANT 10CFR50.46 THIRTY DAY REPORT-ECCS EVALUATION MODEL-REVISIONS Ref erences : 1)
ULNRC-2141 dated 1-19-90 2)
ULNRC-2373 dated 2-28-91 3)
ULNRC-2439 dated 7-19-91 4)
ULNRC-2664 dated 7-16-92 5)
ULNRC-2822 dated 7-15-93 6)
ET-NRC-93-3971 dated 9-21-93 to this letter describes changes to Westinghouse ECCS Evaluation Models which have been implemented for Callaway for the time period from June 1993 to October 1993. provides an ECCS Evaluation Model Margin Assessment which accounts for the peak cladding temperature (PCT) changes resulting from the resolution of the issues described in as they apply to Callaway.
References 1-5 above transmitted prior 10CFR50.46 reports.
Attachment i describes the resolution of those issues which have been implemented for Callaway.
The margin allocations for Callaway to date are identified in Attachment 2.
Based on the criteria and reporting requirements of 10CFR50.46 (a) (3) (ii), as clarified in Section 5.1 of WCAP-13451 Westjagnouse Methodology for Implementation of 10CFR50.4F Reporting," the-cumulative changes since the last 30-day report, Reference 5, are significant for both large break and small brean LOCA and require another 30-day report.
Net benefits have accrued for both large and '
small break LOCA since the issuance of Reference 5.
Since the PCT values determined in the large.and i
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U.S Nuclear RegulatoryJCommission Page 2.
small break LOCA analyses of record, when combined with all PCT margin allocations, remain well below the 2200 F regulatory limit, no reanalysis is' planned by.
Union Electric.
It is noted that a Callaway-specific LOCBART analysis, incorporating the. latest approved models, has been performed to assess the large break LOCA effects and that the small break LOCA significant issues were discussed in Reference 6(i.e.,
- safety, injection flow into the broken loop and the' improved-condensation model).
The Westinghouse Owners' Group is reviewing the small break LOCA issues for possible development of a generic program for resolution.
Should vou have any questions regarding this letter, please contact us.
Very truly yours,
[#'
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/ Donald F.
Schnell
,7 GGY/plh Attachments 1
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cc:
'T.
A.'Baxter, Esq.
Shaw, Pittman, Potts & Trowbridge 2300 N. Street, N.W.
Washington, D.C.
20037 M. H.
Fletcher
'CFA, Inc.
.18225-A Flower Hill Way Gaithersburg, MD 20879-5334 L.
Robert Greger Chief, Reactor Project Branch 1 U.S.
Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 Bruce Bartlett Callaway Resident Office U.S.
Regulatory Commission RR#1 Steedman, Missouri 65077 L. R. Wharton (2)
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 1 White Flint, North, Mail Stop 13E21 11555.Rockville Pike Rockville, MD 20852 Manager, Electric Department Missouri Public Service Commission P.O.
Box 360 Jefferson City, MO 65102
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ULNRC-2892
-i ATTACHMENT ONE CHANGES AFFECTING CALLAWAY LARGE AND' SMALL BREAK LOCA PCT VALUES
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j 1.
MPDATED LOCBART/ FUEL PARAMETERS AND IFBA LOW ROD INTERNAL PRESSURE 1
As,part of the Cycle 7 reload effort, an evaluation'of rod q
internal pressure. issues related to low backfill pressure IFBA fuel was performed.
The_ evaluation required a-
. l Callaway-specific reanalysis of the limiting large break.
clad temperature transient from the current analysis of record.
The calculation incorporated the following:
I revised LOCBART code-(including Grid Model Correct' ions) upgraded fuel parameters BOL Rod Internal Pressure Assumption related to uncertainties in the rod internal pressure calculation and resulted in a net PCT be7efit of 89 F.
Further, the investigation of the effects of low pressure 100 psig IFBA fuel, as used for the feed assemblies in the last several reloads at Callaway, was performed and -a 49 F i
penalty was assessed.
Because of the very low rod internal pressure, the clad does not strain as far from the pellet as at higher pressure.
Further, at very low pressure, a. burst threshold exists.
As such, as pressure is increased and burst occurs, the resulting zirc-water reaction _on both sides of the clad causes a PCT spike.
As pressure _is further increased, the burst temperature is reduced and, subsequently, so is the zirc-water reaction and resulting PCT spike.
Note that this 49 F penalty is of ficially 4
regarded as temporary, pending final closure of this issue; however, it is being reported here since a Callaway-specific analysis was performed.
2.
EFFECTS OF SI IN BROKEN LOOP VS. IMPROVED CONDENSATION MODEL Westinghouse recently completed an evaluation of a potential issue concerning the modeling of Safety Injection (SI) flow into the broken RCS loop for small break loss of coolant accident (SBLOCA).
In previous analyses, Westinghouse assumed that modeling SI flow into the broken RCS loop would result in a lower calculated Peak Cladding Temperature (PCT) since additional SI flow would be expected to provide additional core cooling.
Therefore, in previous analyses, SI flow into the broken RCS loop was modelled as spilling directly into the containment sump to provide conservative PCT results.
Results from recent evaluations indicated that i
for SBLOCA' events using the NOTRUMP ECCS SBLOCA model, modeling SI flow into the broken RCS loop will actually result in a significant increase in PCT. The increase in PCT l
f occurs as a result of competition between the steam venting out the break and the SI to the broken loop, which also exits through the break.
The competition between the steam y
and the SI results in higher RCS pressures and, thus,. lower
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delivered SI flow rates to the intact RCS loops, leading to increased PCT.
While the change in assumption for SI into the RCS broken loop is significant with regard to the effect' on calculated PCT, an offsetting steam condensation benefit has been identified which more than offsets the increase.in-PCT. 'Since the SBLOCA analyses performed by Westinghouse-remain valid and conservative, Westinghouse has elected not-to incorporate these changes into the current NOTRUMP based small break LOCA evaluation models.
In accordance with 10CFR50.46, Westinghouse has notified the NRC of-the impact of these changes.
The basis for Westinghouse's prior assumption on SI flow modeling included consideration for the effect of_back pressure on the spilling ECCS line for cold leg breaks, which would see a higher back pressure for SI connected to the broken RCS loop when compared to spilling against containment back pressure.
Spilling to the higher RCS pressure would increase SI to the intact loops, which is a benefit for PCT.
The effect on intact loop SI flow rates as well as the assumption that some of the SI to the broken loop would aid in RCS/ Core recovery resulted in'the Westinghouse ECCS model assumption that SI to the broken loop was a benefit.
However, when SI is.modeled to enter into the broken loop, a significant PCT penalty is calculated by the-NOTRUMP small break evaluation model (approximately 150 degrees F for a typical Westinghouse 3-9 loop design).
3 An analysis by Westinghouse indicates that the penalty (as described above) occurs as a result of competition between the steam venting out the break and the SI to-the broken loop, which also exits through the break.
The competition between the steam and the SI results in higher RCS pressures for the identical core steaming rates.
Since the ECCS uses centrifugal pumps, higher RCS pressure results in lower delivered SI flow rates to the intact RCS loops, leading to i
the calculated PCT penalty.
This penalty is somewhat aggravated by the use of the Moody two-phase break flow model, which is a thermal equilibrium model being used to model a clearly nonequilibrium process.
However, the penalty is large enough such that a change to a nonequilibrium break flow model would not be expected to offset the break flow-RCS pressure interaction seen when SI is assumed to enter into the broken loop.
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- l However, when a newer conservative model based on prototypic test data is used which modeled the configuration of the SI piping to the RCS cold leg in a Westinghouse designed PWR, a net PCT benefit is calculated.
Improved condensation of the loop steam in the intact loops results in lower RCS pressure and larger SI flow rates.
The increase in SInflow rates, due to lower RCS pressure, leads to the lower calculated PCT.
Thus, the negative effects of SI into the broken loop 2--
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i can be offset by an improved SI condensation model'in'the 5
intact RCS loops.
The improved condensation model is based on data obtained from the COSI test facility.
The COSI test facility is a 1/100 scale representation of the cold leg and SI_ injection:
ports in a Westinghouse designed PWR.
The COSI tests demonstrated that the current NOTRUMP condensation model under-predicted condensation in the intact loops during SI and thus is a conservative model.
Use of the improved condensation model has demonstrated-that the current NOTRUMP small break LOCA analyses without the improved condensation model and no SI into the broken loop.is more conservative (higher calculated PCT) than a case which includes SI into the broken loop and the improved condensation model.
Additionally, the effects of SI in the broken loop have been determined to not change RCP trip symptoms developed in response to USNRC Generic Letters83-10C and 85-12 or SI termination criteria found in the Westinghouse Owners Group Emergency Response Guidelines.
Based on these evaluations, Westinghouse determined that i
this issue does not involve a Substantial Safety Hazard as defined in 10 CFR Part 21.
Reanalyses are not necessary i
since current NOTRUMP based small break LOCA analyses have a conservatively calculated PCT and, therefore, remain valid.
Therefore, Westinghouse is electing at this time not to incorporate these changes into the current NOTRUMP based small break LOCA evaluation models.
Westinghouse has notified the NRC in accordance with 10CFR50.46 (a) (3) (ii).
l This information was also provided to the NRC since
't information in Westinghouse Topical Reports is affected (notification per Westinghouse letter ET-NRC-93-3971 dated 9-21-93).
7 3.
DRIFT FLUX FLOW REGIME ERRORS
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Errors were discovered in both WCAP-10079-P-A and related coding in NOTRUMP subroutine DFCORRS where the improved TRAC-P1 vertical flow regime map is evaluated.
In j
Evaluation Model applications, this model is only used during counter-current flow conditions in vertical flow links.
The affected equation in WCAP-10079-P-A is Equation G-65 which previously allowed for unbounded values of the parameter Cr contrary to the intent of the original source
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of this equation.
This allowed a discontinuity to exist in the flow regime map under some circumstances.
This was corrected by placing an upper limit of 1.3926 on the parameter Cm as reasoned from the discussion in the original source.
As stated, this colteetion returned
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NOTRUMP to consistency.with the original source'for the affected equation.
Furthe'r investigation of the DFCORRS uncovered an additional' closely 5related_ logic error which led;to discontinuities under certain other circumstances.
This error was also corrected and returned the coding.to-consistency:with WCAP-10079-P-A.
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.
Representative plant ca.1-tlations indicated' PCT benefit's j
ranging f rom -13 F to - di For the purposes of tracking 1
PCT, the minimum benefit
_ -13 F has been assigned - to these '
changes.
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ULNRC-2892 ATTACIIMENT TWO ECCS EVALUATION MODEL MARGIN ASSESSMENT FOR CALLAWAY 9
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'l LARGE BREAK LOCA' A.
ANALYSIS OF RECORD.
PCT = 2014 F
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B.
1989 LOCA MODEL ASSESSMENTS
+ 10 F (refer to ULNRC-2141 dated 1-19-90)
C.
1990 LOCA MODEL ASSESSMENTS
+0F (refer to ULNRC-2373-dated 2-28-91)
D.
1991 LOCA MODEL ASSESSMENTS
+ lo p o
(refer to ULNRC-2439 dated 7-19-91)
E.-
1992 LOCA MODEL ASSESSMENTS,-MARGIN
+ 29 F1 ALLOCATIONS, AND SAFETY EVALUATIONS (refer to ULNRC-2664 dated 7-16-92) i F.
1993 LOCA MODEL ASSESSMENTS AND SAFETY
- 25 F h
EVALUATIONS THROUGH JUNE 1993
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(refer to ULNRC-2822 dated 7-15-93)
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CURRENT LOCAL MODEL ASSESSMENTS - OCTOBER 1993 1.
UPDATED LOCBART/ FUEL PARAMETERS
. ggop (refer to: Item 1 of Attachment 1)-
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IFBA LOW ROD INTERNAL PRESSURE
+ 49op I
(refer to Item 1 of Attachment 1) q 3.
POWER SHAPE SENSITIVITY MODEL (PSSM)
+-0F cl (refer to Item 5 of Attachment 1 to ULNRC-2822 dated 7-15-93)-
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LICENSING BASIS PCT + MARGIN ALLOCATIONS =
1998 F NOTES:
1.
The 1992 assessments (total of +31. 7*F) included a LOCA Evaluation Model penalty of +2 F for BOL Rod Internal Pressure Assumption, a LOCA-related margin allocation of
+18.6 F for SG Flow ' Area Seismic /LOCA Tube Collapse, and 10CFR50.59 safety. evaluation penalties of +10 F for
+
Containment Purge Effects and +1.1 F for reconstitution of fuel assembly G87 (applicable only as long as G87 is in the-core).
The current-LOCA model assessments G.1 and G.2 supersede _ the +2 F BOL Rod' Internal Pressure Assumption penalty such that it no longer applies.
Assembly-G87.has been removed from the core and will not be used in-Cycle 7.
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Values have been rounded off to the nearest-degree.
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SMALL BREAK LOCAL A.
ANALYSIS OF RECORD PCT'= 1528 F l
.B.
1989 LOCA MODEL ASSESSMENTS
-+ 229 F-(refer to ULNRC-2141 dated 1-19-90) j C.
1990 LOCA MODEL ASSESSMENTS
+cp'
'o (refer to ULNRC-2373 dated 2-28-91)
D.
1991 LOCA MODEL ASSESSMENTS
+ 77 F1 (refer to ULNRC-2439_ dated 7-19-91) l E.
1992 LOCA MODEL ASSESSMENTS AND SAFETY
+ 0*F2 EVALUATIONS (refer to ULNRC-2664 dated 7-16-92) 1 F..
1993 LOCA MODEL ASSESSMENTS AND SAFETY
+ 4op3 l
=
EVALUATIONS THROUGH JUNE 1993 l
(refer to ULNRC-2822 dated 7-15-93)
G.
CURRENT LOCAL MODEL ASSESSMENTS -
OCTOBER 1993 1.
+ 150 F (refer to Item 2 of Attachment 1) 2.
EFFECT OF IMPROVED CONDENSATION'
. : 15 0 F MODEL (refer to Item 2 of Attachment 1) 3.
DRIFT FLUX FLOW REGIME ERRORS
- 13 F
.l' (refer to Item 3 of Attachment 1) 9 LICENSING BASIS PCT + MARGIN ALLOCATIONS -
1825 F l
NGTES:
1.
See ULNRC-2822 dated 7-15-93, Attachment 2.
2.
A +0.1 F penalty applies as long as reconstituted fuel assembly G87 is in the core.
Assembly G87 has been removed' from the core and will not be used in Cycle 7 3.
The Cycle 6 CRUD Deposition penalty will be carried.until such time as it is evaluated to no longer apply.
.