Uncertainty Analyses Using the MELCOR Uncertainty Analyses Using the - PowerPoint PPT Presentation

Uncertainty Analyses Using the MELCOR Uncertainty Analyses Using the MELCOR Severe Accident Analysis Code Severe Accident Analysis Code Randall O. Gauntt Analysis and Modeling Department, Sandia National Laboratories, Albuquerque NM, 87112, USA +1 (505) 284 3989 rogaunt@sandia.gov CSNI Workshop on the Evaluation of Uncertainties in Relation to Severe Accidents and Level 2 Probabilistic Safety Analysis Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Outline Outline • Background • Methods and tools for uncertainty analysis • Example 1: Computationally intensive uncertainty analysis using LHS sampling • Example 2: Simplified fast running analysis using Monte Carlo sampling • Observations and Conclusions

How Did We Get Here ? How Did We Get Here ? Tier 1: MELCOR Consolidated Ti Tim eline of ne of Nu Nucl clear Integrated Code Codes Ti Tim eline of ne of Nu Nucl clear Tier 2: Mechanistic Codes Sa Safety Te Tech chno nology SCDAP, CONTAIN, VICTORIA Safety Te Sa Tech chno nology Phenomenological Experiments Evolut Ev ution Evolut Ev ution (PBF, ACRR, FLHT, HI/VI, HEVA) Phebus FP, VERCORS European Codes Deterministic Bounding Analysis Probabilistic Risk Informed Analysis Chicago Critical Pile Risk Informed Regulation Atomic Energy Act of 1946 (AEC) Atomic Energy Act of 1954 Chernobyl 9-11-2001 TMI-2 USS Nautilus AEC NUREG-1150 MOX LTA Shippingport revised 1465 1940 1950 1960 1970 1980 1990 2000 2010 NRC NUREG 1465 Windscale NPP Siting Study alternate source term TID 14844 NUREG 0772 source term NP-2010 and Gen-IV Nuclear Technology WASH 1400 Outlook Emerging Issues Optimistic MOX, High Burnup, Life Exension Guarded Environmental Concerns Pessimistic Global Warming and Where are we going ? Where are we going ? Vulnerability to Terrorism

MELCOR: Integrated Severe MELCOR: Integrated Severe Accident Analysis Code Accident Analysis Code • Integrated multi-physics treatment – RCS thermal hydraulic response to transients and loca’s – Core uncovering and heatup – Cladding oxidation and H2 generation – Fission product release from fuel – FP transport and deposition in RCS – Core melt progression and vessel failure – Molten core/concrete interaction – Containment thermal hydraulics – Aerosol mechanics, transport deposition – Hydrogen burns

MELCOR Users Worldwide MELCOR Users Worldwide Finland Russia Sweden Germany Canada Belgium Czech Rep England Slovenia France Hungary Japan USA Spain Italy S. Korea Switzerland Taiwan PRC S. Africa Argentina

MELCOR Uncertainty MELCOR Uncertainty Analysis Analysis Rich access to internal model parameters combined with flexible sequence control access lends MELCOR well to Monte Carlo Uncertainty Analysis Methods MELCOR Statistical MELCOR Batch Execution Analysis MELCOR Uncertainty Software Output Files Software MELCOR sample of distribution Input Files for figure of merit establish randomly uncertainty sample Output File 1 confidence intervals Input File 1 distributions uncertain using non-parametric Output File 2 MELCOR for uncertain parameters Input File 2 method Executable parameters N-times Output File 3 Input File 3 correlation analysis 1 1 1 Output File N Input File N 0 0 values values 0 values

Order Statistics and Order Statistics and Distribution Characterization Distribution Characterization • Monte Carlo sampling produces Percent of observations un-ordered (random) collection With value less than or equal to Z i of observations taken from the true distribution 1% 2% 3% 4% 100% • Z k is collection of rank-ordered Z 1 , Z 2 , Z 3 , Z 4 ,…….. Z 100 observations • Placing “observations” in rank Non-parametric Order Statistics order and calculating the fraction And Confidence Intervals… of observations less than or n equal to a given observation n ! ∑ < ξ = ⋅ − − i n i Pr( Z ) p ( 1 p ) forms an estimate of the CDF − k p i ! ( n i )! = i k • Confidence intervals are estimated based on number of < ξ < = − Pr( Z Z ) Pr( Z ) Pr( Z ) samples and non-parametric i p j i j statistics

Number of Samples Needed Number of Samples Needed • More samples Number of samples required enables greater for desired confidence… percentage of distribution to be − = − ⋅ + + ⋅ n 1 n 1 ( 1 ) C n p n p sampled with higher confidence • To have 95% confidence that Confidence Sample Size to span p = you have sampled Level 99 percent of the (%) 0.9 0.95 0.99 0.999 90 37 76 388 3888 distribution 95 46 93 473 4742 requires 473 99 64 130 661 6635 samples 99.9 88 180 919 9228

MELCOR Uncertainty MELCOR Uncertainty Software Software • User defined MELCOR input uncertainty – Wide range of available distributions • Software produces collection of MELCOR decks by sampling distributions • Batch processing software produces distribution of results

Example 1 Example 1 Computationally Intensive Example Computationally Intensive Example Hydrogen Production Uncertainty in Full System Hydrogen Production Uncertainty in Full System Analysis using LHS Sampling Analysis using LHS Sampling

Motivation for Study Motivation for Study • Hydrogen uncertainty analysis – Motivated by Hydrogen Rulemaking (10CFR50.44) – Provide estimate of range of in-vessel hydrogen expected in Station Blackout – Specific focus: Should hydrogen igniters have backup power in Station Blackout – Issue for Ice Condenser and Mark III plants – Resulted in recommendations for backup • Presentation focus on methodology and recommendations • Deterministic � Probablistic

MELCOR RCS Nodalization Nodalization MELCOR RCS for Station Blackout Sequences for Station Blackout Sequences MSIV MSIV • 3 lumped SG loops CV695 CV598 FL695 (Steam line/turbine) FL595 • 1 single loop with SRV FL690 SRV pressurizer Steam Line FL597 Steam Line FL697 CV599 CV690 FL685 CV590 (Environment) FL585 FL696 FL596 PORV/ADV PORV/ADV CV685 CV585 • Pump seal leakage 450 FL677 FL577 Pressurizer PORV SRV FL679 Relief PRT FL579 450 491 492 • Full loop water Tank CV680 CV612 CV580 CV512 FL607 FL606 F FL506 FL507 0 CV616 L 1 1 6 6 1 CV516 F 1 5 L L F 1 L 5 F 1 circulation 0 CV675 CV575 CV400 CV615 CV515 CV613 CV617 CV611 CV511 CV517 CV513 • Counter current Reactor Vessel FL410 natural circulation FL608 FL509 FL609 FL613 FL612 FL605 FL604 FL504 FL505 FL512 FL513 FL508 FL675 FL575 CV399 with steam CV490 CV510 CV619 CV610 CV519 CV61 CV614 CV518 CV514 8 FL502 FL503 FL6503 F SINGLE L 3 3 FL515 6 F FL615 FL614 0 3-LUMPED L 2 1 1 LOOP 5 FL406 FL405 1 • Creep failure LOOPS 0 0 4 CV500 CV501 CV601 CV600 FL600 FL500 FL501 FL601 CV503 CV502 FL516 CV602 CV603 FL520 FL530 FL517 modeled in SG, FL617 FL616 FL620 CV523 CV522 FL630 CV622 CV623 PUMP FL523 FL624 FL524 PUMP FL623 FL522 hot leg and lower FL622 CV632 CV633 CV534 CV532 PUMP PUMP FL633 FL632 FL532 FL5234 CV620 CV520 head FL533 CV521 CV621 CV320 CV530 CV531 CV630 FL621 CV631 FL521 FL631 FL531

Ice Condenser Containment Ice Condenser Containment Model Model • Multi- compartment containment • Ice beds modeled • Hydrogen burns suppressed

Primary System Pressure in SBO Primary System Pressure in SBO system pressure at relief valve low water in core setpoint reduces steam 18 production and Full loop pressure drops CVH-P.390 natural 16 circulation cools RCS pressurizer empty 14 Pressure [MPa] 12 core material relocation to 10 steam lower head generator dryout 8 accumulator injections 6 accumulator hot leg setpoint 4 nozzle fails by creep rupture 2 0 0 1 2 3 4 5 6 7 8 time [hr]

Vessel Water Level in SBO Vessel Water Level in SBO Hot leg fails and accumulators 7 dump Top of Fuel second 6 boildown of vessel water 5 Water Level [m] lower head failure 4 3 accumulators Bottom of Fuel dribble water in at setpoint 2 1 0 0 1 2 3 4 5 6 7 8 time (hr)

Uncertain Parameters Uncertain Parameters • Uncertain parameters selected based on experience • Parameters included: – Oxidation correlations – Cladding melt release parameters – melt progression – Fuel collapse parameters – Debris quenching parameters – Thermal radiation and heat transfer • LHS sampling of 8 uncertain parameters using 40 samples

Example of Uncertain MELCOR Input Example of Uncertain MELCOR Input Zr Melt Release Temperature 1 LHS Sampling 0.9 Specified Distribution 0.8 Cumulative Distribution 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 2100 2200 2300 2400 2500 2600 2700 Temperature [K]

Uncertainty Analysis for Hydrogen Uncertainty Analysis for Hydrogen Produced in Sequoyah SBO Produced in Sequoyah SBO • LHS sampling 800 produced 700 distribution of 600 results Hydrogen Mass [kg] 500 • Uncertainty 400 band increases 300 with accident progression 200 100 0 0 2 4 6 8 10 12 Time [hr]