ML053080197
| ML053080197 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 10/18/2005 |
| From: | Thadani M NRC/NRR/DLPM/LPD4 |
| To: | |
| Thadani M | |
| Shared Package | |
| ML053080184 | List: |
| References | |
| Download: ML053080197 (46) | |
Text
Application of CPSES Accident Analysis Methodologies to Replacemrent Steam Generators Power October 18, 2005
TXU Power Participants
- b TX U Power Dr. Whee Choe
- Safety Analysis Manager James Boatwright
- Consulting Nuclear Project Manager, Safety Analysis
- Steam Generator Replacement Project NSSS Engineering and Licensing Support Lead Dr. Hugo da Silva u Consulting Thermal-Hydraulics Engineer, Safety Analysis Ben Mays u Steam Generator Replacement Project Manager Denny Buschbaum u Licensing Basis Manager, Regulatory Affairs 2
Agenda t
TX U w40 Power Purpose of today's discussions Overview of the Replacement SG Project a
Replacement SG design description Operating strategy changes Schedules Background on TXU's analysis capabilities and methods Application of TXU's non-LOCA transient analysis methods to the RSG Application of TXU's LOCA analysis methods to the RSG Concluding discussions 3
Purpose
- d TXU "2Power Familiarize NRC reviewers with TXU Power's LOCA and non-LOCA accident analysis methodology topical report supplements supporting TXU's Steam Generator Replacement Project Answer questions to facilitate the review process as much as possible 4
Comanche Peak Steam Electric Station (CPSES)
,TXU Unit 1 Power 4-loop Westinghouse NSSS with large dry containment Part of two-unit site with shared control buildings Originally rated at 3411 MWth, now at 3458 MWth with MUR uprate Current SG: Westinghouse D4 with integral preheater
- Alloy 600 SG tubes
- Approximately 3% tube plugging level Replacement SG: Westinghouse L\\76 with feed ring a Alloy 690 SG tubes During same outage (1 RF12 in Spring, 2007), replace reactor vessel upper head and support structures (missile shield, CRDM cooling ductwork, etc.)
5
Replacement SG Design Features Aft TX U Westinghouse A76 feed ring design Similar to A75 design in use at Shearon Harris and V.C. Summer Relative to D4 SG, the A76 SG has:
- 76,000 ft2 heat transfer area (vs. 48,000 ft2)
- 5532 U-tubes (vs. 4578)
- 3/4" tube OD (same)
- 1.03" triangular pitch (vs. 1.0625" square pitch)
- Top of tube bundle 8 ft higher
- Separate Main feedwater and auxiliary feedwater piping nozzles
- Eliminates delay time for purging AFW lines of hotter MFW fluid 6
Replacement SG Design Features TX U Power Relative to D4 SG, the A76 SG has:
- Essentially the same exterior envelope
- 5330 ft3 Shell-side volume (vs. 5954 ft3)
- Increased Tube Side Volume
- Approximately 825 ft3 additional RCS volume
~8% increase
- Circulation Ratio of - 4 (vs..2.4)
- Slightly larger secondary fluid mass
- 251" narrow range water level span (vs. 233")
7
Replacement SG Design Features A*d TXU
Walef Plenum Hot Leg Cold Leg 8
Replacement SG Design Features Elevated feedring with top discharge nozzles Nozzle holes sized to trap loose parts
- Hole diameter less than tube to tube clearance ll XI S*TOP DISCHARGE SPRAY NOZZLE 12 TXU Power I
A)
---..P I.. I.
A.;
-,fl
- S...
9
Replacement SG Feedwater Distribution Ring
- "' Power (II=nnonno nn 0nnno n
10
Operating Strategy Changes Power Generically, design for a Tavg range of 589.20F to 574.20F Limit Steam Pressure to 1000 psia
- Initially, set full power Tavg - 5850F @ 3458 MWth
- Raise Tavg toward 589.20F as SG heat transfer capability decreases (due to fouling or tube plugging)
Design to a much tighter Tavg range (e.g., +/-1 OF) on cycle-specific basis Lower values of Tavg are intended for future use in Tavg coastdown 11
Schedules March 2007 Supporting Milestones:
January 2005 October 2005 November 2005 March 2006 May 2006 February 2007 Power Steam Generator Replacement Outage Begins Submit Topical Report Supplements Significant "N-1" SGRO prep work during I RF1 I Submit required changes to the Tech Specs NRC approval of Topical Report Supplements Submit any License Amendments identified through 1 OCFR50.59 Evaluations NRC Approval of RSG-related licensing actions 12
Background on TXU's Analysis Capabilities PoweU TXU developed in-house core design and safety analyses methodologies
- CASMO/SIMULATE core design methods
- RETRAN/VIPRE non-LOCA transient analysis methods
- LOCA analysis methods derived from Siemens Power Corp. methods Topical Reports reviewed and approved by NRC
- First topical report approved in 1988
- All were approved by 1993 Used to support 15 reload core configurations for Comanche Peak Steam Electric Station Expertise and models applied to a wide variety of plant support issues including IPE/PRA success criteria, startup testing, simulator qualification, design modification evaluations, resolution of emergent issues, etc.
13
Background on TXU's non-LOCA Analysis TxU Methods Current Non-LOCA methods:
R)(E-89-002-A, "VIPRE-01 Core Thermal-Hydraulic Analysis Methods for Comanche Peak Steam Electric Station Licensing Applications" RXE-91-001-A, "Transient Analysis Methods for Comanche Peak Steam Electric Station Licensing Applications" RXE-91-002-A, "Reactivity Anomaly Events Methodology" TXX-88306, "Steam Generator Tube Rupture Analysis" RXE-91-005-A, "Methodology for Reactor Core Response to Steamline Break Events" RXE-94-001-A, "Safety Analysis of Postulated Inadvertent Boron Dilution Event in Modes 3, 4, and 5" 14
Background on TXU's non-LOCA Analysis Po TxU Methods Each topical report was individually reviewed and approved; however,...
Through the RAI process, the scope of RXE-91-001-A came to include the generalized non-LOCA accident analysis methodology Now consider RXE-91-001-A to be the "umbrella" non-LOCA topical report To address generic activities such as the replacement SG, consider a supplement to RXE-91-001-A to be appropriate 15
Background on TXU's non-LOCA Analysis TPowxe Methods Currently licensed approach to SG models:
- Single-node model used in SGTR and SLB analyses
- Three-node model used in other non-LOCA analyses
- Internal recirculation loop is not modeled
- Detailed, multi-node model used to determine mass equivalency for simulating SG water level trip functions Coarsely-noded model justified through comparisons of integrated system responses to CPSES transient data 16
Background on TXU's non-LOCA Analysis Methods Any Questions or Comments?
M TXwU ByPower 17
Application of TXU's non-LOCA transient Por TXU analysis methods to the RSG Power During initial RSG project planning, all topical reports reviewed to assess effects of RSG on approved analysis and model methods X Analysis and modeling methods remain applicable
- For those analyses which are relatively insensitive to the SG model, still required to update SG model with replacement SG geometrical attributes
- For those analyses which show some sensitivity to the SG model, require a different SG model (preheater vs. feed ring)
- Conforming modifications to SG water level trip functions Also assessed the effects of the replacement SG on the course of transients and accidents Only feedwater line break has any relevant differences
- Due to elevated feed ring, early transient response similar to steam line break 18
Application of TXU's non-LOCA transient analysis methods to the RSG Pwer TXU Due to extensive discussions of decision made to submit topical approved TXU methods to feed preheat SG design in RXE-91-001-A, report supplement to describe application of ring SG design Current methods will continue to be used to support Unit 2 1.9
Topical Report Supplement PowXeU ERX-04-005, "Application of TXU Power's Non-LOCA Transient Analysis Methodologies to a Feed Ring Steam Generator Design" ERX-04-005 supplements the approved TXU non-LOCA transient analysis methodology topical reports (via RXE-91-001-A)
Included in the supplement:
- Assessments of effects of the replacement SG on the transient-specific methodology
- Identification of new models required for specific analyses
- Assessment of transients with different phenomena or sequence of events
- Demonstration analysis of the feedwater line break accident 20
Assessments of effects of the replacement SG on the non-LOCA analysis methodology General analysis methodology remains applicable Po TXU v44l-"r Power For each transient or accident:
a Ensure important phenomena are modeled a Identify conservative initial conditions and equipment performance characteristics for each relevant event acceptance criterion
- Consider loss of offsite power where required a Identify limiting single active failure 21
Identification of different required models Ad TXU Power Generically:
a Modify coarse-node SG to remove preheater (if previously modeled)
- Necessitates a different SG model 22
Assessment of transients with different il TXU phenomena or sequence of events Only feedwater line break identified as different FLB with a preheat SG:
- Initially, saturated liquid blowdown through preheater box with integral flow restrictors in the feedwater nozzle
- Essentially, the SG inventory is being drained
- Relatively little heat removal due to low-quality fluid discharge FLB with a feed ring SG:
- Short duration of saturated fluid relief through flow distribution nozzles and into the feed ring, exiting the SG through a nozzle with no flow restrictors
- Once flow distribution nozzles uncover (very quickly in accident),
saturated steam blow down (similar to steam line break)
- After inventory is exhausted, heatup is similar to preheat SG, but greater RCS cooldown has previously occurred 23
SG model changes tP-4 TXU Power For FLB analyses, chose to adopt feed ring SG model developed by Westinghouse
- Relatively detailed model including the internal recirculation loop
- Based on RETRAN-02
- Benchmarked against plant data
- Model methodology reviewed and approved by NRC
- Widely used by Westinghouse
- Demonstrated to be robust through internal testing Noding diagram is contained in WCAP-14882-P-A (Westinghouse proprietary)
For configuration control convenience, chose to use this model for all non-LOCA transients and accidents except for SGTR and SLB 24
SG water level model changes TX U Power For the LOAC and LOFW analyses, detailed vendor design information used to assess the mass equivalency for the SG water level -low-low trip functions w Essentially the same as current practice for determining mass equivalency For the FLB analysis, SG water level indication based on AP between instrument tap locations Corrected for limitations of the model
- Lower tap is near bottom of a homogenous volume, which results in an artificially high mass between tap elevations Approach is essentially the same as that currently used with TXU's detailed SG model when determining the mass equivalency for the coarsely-noded SG model 25
TXU Power Due to early uncovery of elevated feed ring, early transient response similar to steam line break The RSG feedwater line break event results in:
- Initial cooldown as faulted SG depressurizes
- Subsequent Reactor Coolant System heatup due to degradation of heat sink
- Ultimate mitigation when auxiliary feedwater flow is sufficient to remove decay heat Limiting single failure remains in the Auxiliary Feedwater System where:
- One motor-driven auxiliary feedwater pump is assumed to feed only the faulted SG, with no credit for heat removal
- The second motor-driven auxiliary feedwater pump (feeding two intact SGs) is the assumed single failure
- The turbine-driven auxiliary feedwater pump requires a steam generator water level -low-low signal in two or more SGs to start 26
RSG Feedwater line break PoeTXU For larger break sizes, the rapid steam pressure decrease leads to early steam line isolation and safety injection actuation u Significant delay in obtaining 2nd steam generator water level - low-low signals from intact, isolated steam generators For smaller break sizes, the low steam pressure setpoint may not be reached for several minutes, but MFW can still be delivered to intact steam generators a Loss of heat sink effects bounded by maximum break size 27
Feedwater line break - Comparisons to D4 analyses Power 7000 6000 I 5000
-J tu 4000 o 3000 LA.
2000 0:
100 100 1000 TIME (SEC) 10000 1.0 0.8 O 0.6 0-J LA I
0.4 0.2 0.0 10 100 1000 TIME (SEC) 10000 28
Feedwater line break - Comparisons to D4 analyses a TXU w412 Power 120000 100000
-J cn 80000 En C) 60000 U) aw 6, 40000 AL LL
< 20000 0
100 200 300 400 TIME (SEC) 600 600 700 2600 to 2400
" 2200 UJw 0:
W 2000 N
U) t3 1800 a1 1600 10 100 1000 TIME (SEC) 10000 29
Feedwater line break - Comparisons to D4 analyses
, TXwU Z 1400 V-(, 1200 w
cc 3 1000 n
U)
LU W 800 0
I-600 (9Z 400 F
200 en 0
10 100 1000 TIME (SEC) 10000 30
Summary of non-LOCA Topical Report
< TXU Supplement Power Descriptions of original and replacement SG designs and characteristics Assessments of the effects of the replacement SG on the approved non-LOCA accident analysis methodologies Discussion of the replacement SG model Description of the revised feedwater line break analysis methodology
- Including comparisons of sample analysis results to results with original SG 31
RSG Supplement to TXU's LOCA Methodologies Power Hugo C. da Silva October 18, 2005
Purpose:
T X U Familiarize NRC Reviewers with TXU's LOCA Topical ERX-04-004 entitled:
"Replacement Steam Generator Supplement to TXU Power's Large and Small Break Loss-of-Coolant Accident Methodologies" TXU already has NRC-approved ECCS Evaluation Models for Large and Small Break LOCA
- TXU is requesting that this topical be considered as a supplement to be applied only to Unit 1 with the Replacement A-76 SG's
- The methodology changes proposed are simply due to the new RSG design
- The existing NRC-approved methodologies will continue to be applied unchanged to Unit 2 with the current D-5 SG's 33
Approach:
TXU Power
- A differential approach was adopted for the Topical Report.
- Only the methodology changes are presented. The unchanged parts of the methodology are not repeated. The changes are those required by the new RSG design.
- This approach was intended to streamline the topical and its review.
- This approach also avoids the need to make portions of this topical proprietary by referencing proprietary figures and statements in previously NRC-approved topical reports.
- Still, this Topical Report includes a complete set of demonstration analyses for both Large Break and Small Break LOCA.
- The demonstration analyses have the same scope, i.e., include all the same relevant sensitivities, as the analyses submitted to the NRC with the original methodologies.
34
Affected Elements:
g& TXU Power i Small Break LOCA
- Only the system thermal-hydraulic response was potentially affected.
Therefore, the ANF-RELAP input was the only thing changed.
- Large Break LOCA
- Only the system thermal-hydraulic response was potentially affected.
Thus, only RELAP4 and REFLEX inputs were affected.
35
LBLOCA (RELAP4 & REFLEX) Model Changes:
aft TXU v44sW Power a Replaced existing steam generator geometry with A-76 geometry
- The existing nodalization structure was preserved.
- The Large Break remains the LIMITING LOCA 36
LBLOCA Demonstration Analyses:
AM TXU v',ZV Power
- Break spectrum (required by Appendix K)
- 3 Split breaks cases were run (A = 2.0, 1.6 & 1.0 x Cold Leg Area).
- 3 DEG breaks cases were run (CD = 1.0, 0.8 and 0.6).
- CD = 1.0 was limiting and became the "Base Case"
- Single failure
- Loss of I ECCS train vs. Loss of 1 train of LPI (RHR)
- Loss of 1 train of RHR was limiting
- Convergence criterion (Optional)
- Varied RELAP4 convergence criterion, ESPW = 0.5 -> 0.25
- Little difference between cases, shows robustness.
37
LBLOCA RSG A-76 vs. D-4 Results:
TXU Power
- PCT occurs slightly earlier in the A-76 than in the D-4
- This is due to the larger RCS volume inventory in the A-76, which retains more water at the end of blowdown and therefore quenches sooner.
- As a result, the PCT is lower in the A-76 than in the D-4.
- Sensitivities lead to the same conclusions in the A-76 and the D-4
- Break Spectrum: DEG break with CD = 1.0 remains limiting
- Single Failure: Loss of 1 train of RHR remains limiting
SBLOCA (ANF-RELAP) Model Changes:
Ai, TXU Power a Replaced existing steam generator geometry with A-76 geometry
- The existing nodalization structure was preserved.
- No MFW "purge" flow in the RSG. Might impact loop seal clearing.
- Minor change in the upper downcomer (Fig. 2.3 of RXE-95-001-P-A)
- Combined previously-split volumes to improve robustness 39
SBLOCA Demonstration Analyses:
- o> TXU v4~FPower
- Break spectrum (required by Appendix K)
- 3 inch, 4 inch and 5 inch breaks were run.
- 4 inch was limiting and became the "Base Case"
- Cross-flow sensitivity study (required by Methodology)
- Same as in previous topical report (RXE-95-001-P-A).
- Study was performed for the "Base Case".
- Little difference from varying the X-flow K. Nominal "K" was limiting.
- Time step sensitivity study (optional)
- Only required by the methodology if certain criteria are met. They were not. However, this study was performed anyway.
- Study was performed for all break sizes.
- Little difference between cases, shows robustness.
- Selected time step was limiting.
40
SBLOCA RSG A-76 vs. D-4 Results:
A-MV. owTXU
- Break Spectrum (Required by Appendix K)
- 4 inch limiting for A-76 whereas 3 inch limiting for D-4.
- This is due to differences in transient liquid distributions, consistent with the A-76's larger RCS volume & taller tube bundle
- Cross-flow sensitivity study
- Similar conclusions to previous (D-4) topical report:
- Nominal K remains more limiting than 1 OxK and K/1 0
- Differences between results varying K were not significant
- Time step sensitivity study
- Similar conclusions to previous (D-4) topical report:
- Differences between results varying time step were not significant.
- Selected time step remains limiting 41
SBLOCA RSG Break Spectrum Results:
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TPower CPSES-1 SBLOCA D76 RSG Inch Break 14.0 12.0
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0 500 1000 Time (sec) 1500 2000 0
500 1000 Time (sec) 1500 2000 42
SBLOCA RSG X-Flow & Time Step Sensitivities:
CPSES-1 SBLOCA D.76 RSG Inch Break - XfMow Study
- TXU v'40%y Power 2000.0 1800.0 1600.0 c1400.0 C
e 1200.0 E 1000.0 a)
E 800.0 C)
F 600.0 400.0 200.0 0.0 0
200 400 600 800 1000 Time (sec) 1200 CPSES-1 SBLOCA D-76 RSG inch Break - Time Step Study 2000.0 1800.0 1600.0 C-1400.0 0I
- 1200.0 E 1000.0 as E 800.0 cQ F 600.0 400.0 200.0 0.0 I
I I
I I
+
0 200 400 600 Time (sac) 800 1000 1200 43
LOCA Overall Conclusions
,TXpoTXU Power For BOTH the Large and Small Break LOCA:
- Only system thermal-hydraulic response was potentially affected
- A complete set of demonstration analyses was performed
- Larger RCS volume -÷ higher post-blowdown lower plenum inventory
- SBLOCA limiting break 4 inch in the A-76 vs 3 inch in the D-4
- A-76's larger RCS volume & taller tube bundle -*
differences in RCS transient liquid distributions
- The proposed methodologies are essentially the same as those previously approved and extensively used for both CPSES units with Model D SGs 44
General Discussions ovE TXU Power Any Comments or Questions?
45
Summary 6<& TXU Power TXU Power's non-LOCA and LOCA analysis methods have been reviewed and approved by the NRC Analysis methods have been applied to support 15 reload core configurations for CPSES since 1993 Similar methods and models have been used extensively for a variety of plant-support applications TXU engineers are well-versed in the use of these tools, which provide good representation of the design and operation of CPSES Extending the application of these methods to feed ring SG design Assessed the continued applicability of the methods Updated models where appropriate Continue to apply same proven methods and modeling approaches to RSG 46