Evaluation of System Success Criteria Using MELCORCriteria Using MELCOR
Presented by:Don Helton (NRC)
MAAP Users Group MeetingJanuary 21, 2010
Charlotte, North Carolina
Presentation Outline
• Overview• Completed activities:
– Core damage surrogate comparisons
2MUG Meeting, January 21, 2010
– Success criteria MELCOR analysis• Ongoing activities
– Incorporation of insights in to SPAR models– Investigation of related issues
• Future activities:– Additional analyses– Interactions with industry - ?
Success Criteria Project
• Staff has begun using MELCOR to investigate a limited set of PRA success criteria issues
• Team is comprised of a diverse group of contributors– Project Management: Don Helton (RES)– MELCOR Analysis: Hossein Esmaili (RES)– Calculation Matrix: Don Dube (NRO) Rick Sherry (retired) et al
3MUG Meeting, January 21, 2010
Calculation Matrix: Don Dube (NRO), Rick Sherry (retired), et al.– Systems Analysis Support: Don Marksberry (RES), Bob Buell
(INL)– SPAR Models: Pete Appignani (RES), Bob Buell (INL)– Investigation of related modeling issues: KC Wagner (SNL), Tim
Wheeler (SNL), Jeff LaChance (SNL)– HRA Support: James Chang (RES)– Operations Support: Gary Callaway (TTC), Rick Devercelly
(TTC)
Realized and Expected Benefits
• Improves technical basis for selected SPAR success criteria (i.e., enhances realism in SDP Phase 3 analyses)
• In-house components facilitate knowledge transfer
• Enhances in-house expertise available to consult Senior Risk Analysts and other technical offices
4MUG Meeting, January 21, 2010
• Promotes greater collaboration between thermal-hydraulic and PRA analysts
SPAR Model Background• SPAR = Standardized Plant Analysis Risk models• NRC PRAs used by NRC staff in support of risk-informed activities
related to– the inspection program and incident investigation program;– performance indicator verification;– accident sequence precursor program;
5MUG Meeting, January 21, 2010
q p p g ;– generic safety issues and special studies; and– operating experience
• 77 SPAR models representing the 104 US plants– All have Level 1 internal events– Some have external events models, low-power/shutdown models and/or
Level 2 feasibility models• Most success criteria are based on the SDP Notebook plant visits or
cutset-level comparisons to licensee PRA models• Two SPAR models were recently peer reviewed by industry-led peer
review teams
Level 1 End-State Project
NRC/RES and SNL
NRC Success Criteria Project
NRC/RES and INL SPAR Model Success Criteria Changes
MELCOR Code and Input Model Development
NRC/RES and SNL
Relationship w/ Related Activities
6MUG Meeting, January 21, 2010
Support and guidance from technical office (NRR) and the Technical Training Center
g
NRC/RES and INL
Main SPAR Model Program, SDP SPAR Model Use, and the Risk Assessment Standardization Project
NRC/RES, NRC/NRR, Regional Senior Risk Analysts, and INL
Potential NRC/Industry Collaboration
NRC/EPRI MOU:MAAP User’s Group:
State-of-the-Art Reactor Consequence Analyses Project
NRC/RES and SNL
Presentation Outline
••• OverviewOverviewOverview• Completed activities:
– Core damage surrogate comparisons
7MUG Meeting, January 21, 2010
– Success criteria MELCOR analysis••• Ongoing activitiesOngoing activitiesOngoing activities
––– Incorporation of insights in to SPAR modelsIncorporation of insights in to SPAR modelsIncorporation of insights in to SPAR models––– Investigation of related issuesInvestigation of related issuesInvestigation of related issues
••• Future activities:Future activities:Future activities:––– Additional analysesAdditional analysesAdditional analyses––– Interactions with industry Interactions with industry Interactions with industry --- ???
Core Damage Surrogate Comparison
• MELCOR analyses performed to look at various core damage surrogates– 1204 C (2200 F) selected for confirmatory analyses for PWRs and
BWRs
• Included PWRSBO and hotleg LOCAs, and
8MUG Meeting, January 21, 2010
BWR SBO andrecirculationline LOCAs
• Additionalsurrogatecomparisonsplanned in2010
Success Criteria MELCOR Analysis
• Detailed SOARCA MELCOR 1.8.6 models for Surry and Peach Bottom used
• Many calculations intentionally assume minimal operator action and are allowed to proceed to core damage to:– Establish minimal equipment configurations – Establish timings for human error probability (HEP) evaluations– Establish time window for AC power recovery
F th b lt d t d t th b t
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• For the above reason, many results do not correspond to the best-estimate integrated plant response to a given initiator; they do correspond to the best-estimate simulation given the prescribed boundary conditions
• Analyses are confirmatory in nature:– Detailed and insightful, but should not be viewed as licensing
calculations• Results are documented in an August 2009 report available in the
NRC’s Agencywide Document Accession and Management System (ADAMS) at accession number ML091890792
Surry Calculation Matrix
• Small LOCA dependency on sump recirculation– Effect of sprays on RWST depletion
– Does the system depressurize (and how fast)?
• Feed & Bleed PORV success criteria– Combination of HHSI and PORVs
• Steam Generator Tube Rupture
10MUG Meeting, January 21, 2010
– Multiple tube ruptures
– Impact of secondary cooling, HHSI, forced cool down
• Station blackout– Investigating time available for AC power recovery
– Both small and large RCP leaks with and without TD-AFW
• Accumulator injection– Spectrum of LOCA sizes
– Availability of HHSI/LHSI in conjunction with number of accumulators
Surry Example - Feed and Bleed
• 1 SI + 1 PORV sufficient:– Operators secure
containment sprays
– At Surry, HHSI will lift PORV (no operator action required)
– SI initiates on high t i t ( 2 0
2
4
6
8
10
12
14
16
18
Pres
sure
[MPa
]
SG A
SG B
SG C
PRZ
11MUG Meeting, January 21, 2010
containment pressure (~2 hrs)
– In absence of HHSI recirc., core damage at ~ 13.5 hrs (~4 hrs after RWST depletion)
• Note that Surry has the lowest power level of the 3-loop plants with HHSI
0
0 10000 20000 30000 40000 50000
time [sec]
0
5
10
15
20
25
0 10000 20000 30000 40000 50000
time [sec]
Rea
ctor
Wat
er L
evel
(m)
PRZDCRing 1BAFTAF
Peach Bottom Calculation Matrix
• Inadvertently Open SRV– Can HPCI/RCIC/CRD maintain cooling until low pressure system
injects?
• Station blackout (RCIC/HPCI availability)– Investigating time available for AC power recovery
S S
12MUG Meeting, January 21, 2010
– Suppression pool heatup and pump NPSH limit
Peach Bottom Example –Station Blackout
Case RCIC HPCI AC/DCSRV
SticksOpen?*
HTCLDepress.?
Core Uncover
(hr)
Core Damage
(hr)
1
No
No No
No
0.5 1.2
1a Recover at 1.2 hrs No 0.5 No
2 No t=0 0.3 0.8
13MUG Meeting, January 21, 2010
No3
Yes
Infinite DC No 17.7 19.44 Infinite DC No Yes 5.6 7.2
5 2 hrs DC No
No
3.3 4.3
6 Infinite DC Yes 5.6 7.27
No Yes
Infinite DC No 17.5 19.3
8 Infinite DC No Yes 9.1 10.8
9 2 hrs DC NoNo
3.8 4.910 Infinite DC Yes 8.9 10.7
No operator action unless specified* Before core damage
Peach Bottom Example (cntd.) –AC recovery sensitivity
• Sensitivity to power recovery
• Case 1a (HPCI/RCIC/CRD/LPCI become available)
ADS Activated
14MUG Meeting, January 21, 2010
HPCI/RCIC/CRD InjectionLPCI Injection
Presentation Outline
••• OverviewOverviewOverview••• Completed activities:Completed activities:Completed activities:
––– Core damage surrogate comparisonsCore damage surrogate comparisonsCore damage surrogate comparisons
15MUG Meeting, January 21, 2010
––– Success criteria MELCOR analysisSuccess criteria MELCOR analysisSuccess criteria MELCOR analysis• Ongoing activities
– Incorporation of insights in to SPAR models– Investigation of related issues
••• Future activities:Future activities:Future activities:––– Additional analysesAdditional analysesAdditional analyses––– Interactions with industry Interactions with industry Interactions with industry --- ???
SPAR Model Changes
• Updating bleed success criteria in 6 PWR models
• Updating LOCA early injection success it i i 6 PWR d l
16MUG Meeting, January 21, 2010
criteria in 6 PWR models• Potential changes to SBO core uncovery
timings in most BWR models (excludes BWR/5&6)– Current modeling philosophy of failure after
battery depletion limits benefit• Additional changes possible pending
supplementary analysis
Investigation of Related Issues
• Ongoing project at SNL to investigate:– Scope importance of PRA and T/H modeling
assumptions for a few specific sequences
17MUG Meeting, January 21, 2010
– Additional surrogate timing comparisons– Necessary time to arrest fuel heatup upon AC
power recovery
• Mostly at-power, but work plan calls for limited shutdown analysis
• Majority of work to be completed in 2010
Presentation Outline
••• OverviewOverviewOverview••• Completed activities:Completed activities:Completed activities:
––– Core damage surrogate comparisonsCore damage surrogate comparisonsCore damage surrogate comparisons
18MUG Meeting, January 21, 2010
––– Success criteria MELCOR analysisSuccess criteria MELCOR analysisSuccess criteria MELCOR analysis••• Ongoing activitiesOngoing activitiesOngoing activities
––– Incorporation of insights in to SPAR modelsIncorporation of insights in to SPAR modelsIncorporation of insights in to SPAR models––– Investigation of related issuesInvestigation of related issuesInvestigation of related issues
• Future activities:– Additional analyses– Interactions with industry - ?
Additional Analyses
• Some additional Surry and Peach Bottom analysis planned
E ff t f l l # f
19MUG Meeting, January 21, 2010
– E.g., effect of power level on # of PORVs for feed and bleed
– Upgraded version of August 2009 report envisioned
• Additional analysis planned for a 4-loop Westinghouse large, dry plant
Interactions w/ Industry
• A number of opportunities have arisen for cursory information exchanges:– 2009 RIC conference
20MUG Meeting, January 21, 2010
2009 RIC conference
– EPRI/NRC research information meetings
– 2009 MCAP/CSARP meeting
– This MAAP User Group meeting
• More detailed exchanges comparing results for specific sequences of interest might benefit both sides
Concluding Remarks
• Application of MELCOR to update basis for PRA treatment of specific operator timing and mitigation system effectiveness issues of interest
• Work underway to establish basis for SPAR model changes
Work recently commenced at SNL to look at additional
21MUG Meeting, January 21, 2010
• Work recently commenced at SNL to look at additional aspects (e.g., core damage surrogates)
• Extension to other plants (e.g., 4-loop large, dry)
• Possible future interactions with industry
Acronyms
MAAP Modular Accident Analysis ProgramMCAP MELCOR Code Assessment ProgramMOU Memorandum of UnderstandingNPSH Net Positive Suction HeadNRC US Nuclear Regulatory CommissionNRO Office of New ReactorsNRR Office of Nuclear Reactor RegulationPORV Power (or Pilot) Operated Relief ValvePRA Probabilistic Risk AssessmentPWR Pressurized water reactorRCIC Reactor Core Isolation CoolingRCP Reactor coolant pump
22MUG Meeting, January 21, 2010
RES Office of Nuclear Regulatory Research
RIC Regulatory Information ConferenceRWST Refueling Water Storage TankSBO Station blackoutSDP Significance Determination ProcessSNL Sandia National LaboratoriesSOARCA State-of-the-Art Reactor
Consequence AnalysesSPAR Standardized Plant Analysis RiskSRV Safety Relief ValveTD-AFW Turbine-Driven Auxiliary FeedwaterT/H Thermal-hydraulicTTC Technical Training Center
AC Alternating CurrentBWR Boiling water reactorCRD Control Rod DriveCSARP Cooperative Severe Accident
Research ProgramEPRI Electric Power Research InstituteHHSI High-Head Safety InjectionHPCI High Pressure Coolant InjectionINL Idaho National LaboratoryLHSI Low-Head Safety InjectionLOCA Loss-of-Coolant Accident