evaluation of system success criteria using melcorusing melcor

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


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


• 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;


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


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


••• OverviewOverviewOverview• Completed activities:

– Core damage surrogate comparisons


– 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


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


• 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


– 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


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


– 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


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


HPCI/RCIC/CRD InjectionLPCI Injection


••• OverviewOverviewOverview••• Completed activities:Completed activities:Completed activities:

––– Core damage surrogate comparisonsCore damage surrogate comparisonsCore damage surrogate comparisons


––– 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


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


– 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


••• OverviewOverviewOverview••• Completed activities:Completed activities:Completed activities:

––– Core damage surrogate comparisonsCore damage surrogate comparisonsCore damage surrogate comparisons


––– 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


– 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


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


• 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


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

evaluation of system success criteria using melcorusing melcor

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