MELCOR Best Practices - An Accident Sequence Walkthrough L. … · 2020. 1. 9. · SRV seizure...

Vg# 1

MELCOR Best Practices - An Accident Sequence Walkthrough

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.

Larry Humphries, K. Wagner, J. Jun, R. Gauntt (SNL)

and

Hossein Esmaili (NRC)

Vg# 2

Best Practices adopted for NRC SOARCA Program

• State of the Art Reactor Consequence Analyses (SOARCA)

– Realistic evaluation of severe accident progression, radiological releases and offsite consequences• Provide a more accurate assessment of potential offsite consequences

– Focus on a spectrum of scenarios most likely to contribute to release and subsequent offsite consequences, using a risk-informed approach

• SOARCA expert review panel meeting– Solicit discussion from experts

• Experts also supplied additional recommendations– Discussion of base case approach on some key complex

and uncertain events for MELCOR calculations– Best Practices distilled from these findings

• Model defaults updated as result of this work• Uncertainty recognized as important

– Separate task evaluting uncertainty using uncertainty engine

•Introduction•BWR•PWR•Other Best Practices

Vg# 3

BWR Topics for Consideration

1. Thermal response and seizure of cycling S/RVs during late phase of in-vessel fuel damage

2. Criteria for representing mechanical failure of highly-oxidized but erect fuel assemblies

3. Volatile fission product speciation

4. Structural (non-radioactive) aerosol generation

5. Aerosol deposition on reactor and containment surfaces

6. Debris heat transfer in reactor vessel lower plenum

7. RPV failure mode and criteria in heads with varied and multiple penetrations

8. Hydrogen combustion and ignition

9. Debris spreading and Mark I shell melt-through

10. Under-cutting of reactor pedestal wall via long-term molten corium-concrete interaction

•Introduction•BWR

– LTSBO– Nodalization1.S/RV2.Fuel rod Failure3.Volatile FP

speciation4.Structural aerosol5.Aerosol Deposition6.Debris HTF in LP7.RPV failure with

penetrations8.H2 combustion9.Debris Spreading

(Cavity)10.MCCI

•PWR•Other Best Practices

Vg# 4

BWR Walk-through: BWR/4 Mark I LT-SBO

• Total loss of off-site power

• RCIC operation on batteries for 8 hrs

• Manual S/RV control available, but partial depressurization not reflected in the example calculation

• Containment venting not available due to loss of power





(Cavity)10.MCCI


Vg# 5

BWR/4 Reactor Vessel Model

LOOP A

FL387

FL383

FL385

LOOP B

FL384

FL382

FL614

CSTCV360

Steam Dome

CV320Lower Plenum

FL304

CV310Downcomer

CV310Downcomer

CV

383

CV

385

CV

384

CV

382

FL386

FL312FL312

CV

300

CV

300

FL310FL311

FL356

FL3

57

FL370 CV391Turbine / Hotwell

(time independent)

InboardMSIVs

FL371

FWPump

CV392Feedwater source(time independent)

CRDPump

RCIC

Core Spray(Loop 1)

CV600

FL372

FL702

FL706

FL606

CV370 (Steam Lines)

FL399(RV Breach)

CV350 Steam Separators

SVs(2 valves)

FL9

10(W

etw

ell

Ven

t)

to drywellatmosphere

CV200Drywell

CV220

CV901Environment

FL359 - FL369

FL358

FL653

RHR-2 RHR-1

HPSW

FL6

48

FL6

49

FL652

SPRSR01

CV652

CV

651

CV

650

CV

700

ReactorBuildingRWCU return

(not modeled)

CV374 CV372

FL611

FL376 FL374

CV220

CV653FL656 (LPCI)

FL655(supp.poolcooling)

FL657(LPCI)

FL654(supp.poolcooling)

CV394(time

independentkeep-full at

steady state)

S/RV (typical)11 parallel valves

TurbineBuilding

FL6

00

FL6

13

CV611

FL351

FL699

FL391(RWCUbreak)

FL6

51

FL6

50

A CB D

CV355Steam Dryers

FL355FL352

FL704

SPRSR02CV631

HPCI

FL6

33

FL631

FL626

FL634

CV345 Shroud Dome

FL345

• BWR/4 Reactor Vessel Model

– Important features & components

– Nodalization

• Reactor Coolant System

• Cavity Model

– Elevation View

– Aerial View





(Cavity)10.MCCI


Vg# 6

0

100

200

300

400

500

600

700

0 5 10 15 20 25 30

time [hr]

Wat

er L

evel

[in]

Top of Jet Pumps

Lower core plate failure:debris relocation

into lower head

DowncomerCore Region

Top of Active Fuel

Bottom of Active Fuel

Automatic operation of RCIC

Base of downcomer

RPV lower head failure

LT-SBO: Early Thermal-Hydraulic Response

Sequence characteristics:

• 0 – 8 hrs: RCIC operates to maintain water level

• Controlled depress. does not occur to maintain RCIC steam supply

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30

time [hr]

Pre

ssur

e [p

si]

Containment Failure(drywell shell melt -through)

S/RV seizes open

Local failure of lowercore support plate(initial debris relocationinto lower head)

Cycling of lowest setpoint S/RV

Cooling from automaticcycles of RCIC

RPV lower head failure

1•Introduction•BWR




(Cavity)10.MCCI


Vg# 7

S/RV Seizure at High Temperature

• Automatic S/RV actuation after battery depletion

• Typically a single cycling valve

• Demand frequency: One cycle every 3-4 min at onset of core damage

• Steam/H2 discharge with variable temperatures

• Gas temperature exceeds 1000 K close to time of lower core plate failure

500

600

700

800

900

1000

1100

1200

1300

1400

1500

0 5 10 15 20 25 30

time [hr]

Tem

pera

ture

[K]

Core Exit Gas

Gases discharged through S/RV(s)

S/RV seizes (10 cycles over 1000K) 1


–LTSBO–Nodalization1.S/RV

1.Seizure @ high temperature

2.Valve designs1.depressurization rate

2.FP transport

2.Fuel rod Failure3.Volatile FP speciation

4.Structural aerosol5.Aerosol Deposition6.Debris HTF in LP7.RPV failure with penetrations

8.H2 combustion9.Debris Spreading (Cavity)

10.MCCI


Vg# 8

Valve Design Affects Response

• BWR/5 and /6: Spring-actuated, direct-acting relief valves [Crosby or Dikkers]

– Disk opens to position proportional to pressure against spring

– Model: Seize in last position based on residual lifetime

• 60 min @ 1000 K

• 30 min @ 1500 K

• BWR/3 and /4: 2- or 3-Stage Target Rock Pilot-Operated relief valves

– Valve disk cycles between full-open & full-closed

– Model: Seize in open position at 10th

cycle above 1000 K

PBAPS (3-stage TR) GGNS





2.FP transport




10.MCCI


Vg# 9

0

0.2

0.4

0.6

0.8

1

1.2

-2 -1 0 1 2 3 4 5 6

time [hr]

Fra

ctio

n of

Ful

l-Ope

n P

ositi

onLowest Setpoint SRV

Stem Position

time [hr]

Depressurization Rate Depends on Valve Position at Seizure

0

200

400

600

800

1000

1200

1400

-2 -1 0 1 2 3 4 5 6

time [hr]

Pre

ssur

e [p

si]

GGNS (Dikkers spring-actuated)

PBAPS (3-stage T-R)

Reactor Vessel Pressure

SRV seizure





2.FP transport




10.MCCI


Vg# 10

Pressure History Influences Fission Product Transport / Deposition

0

0.1

0.2

0.3

0.4

-2 -1 0 1 2 3 4 5 6

time [hr]

Fra

ctio

n of

Initi

al C

ore

Inve

ntor

y

PBAPS

Iodine Released from RCS(to suppression pool via open SRV)

SRV seizure

GGNS

[Release fraction normalized to zero at time of SRV seizure]

GGNS

Vessel breach

PBAPS

RPV dryout





2.FP transport




10.MCCI


Vg# 11

Core Response to Oxidation Transient

500

1000

1500

2000

2500

10 11 12 13 14 15 16 17 18

time [hr]

Tem

pera

ture

[K]

Top of Core (axial level 15)

Middle of Core (axial level 12)

Bottom of Core (axial level 8)

Ring 1

Water level in shroud below

2/3 core height

Fuel assembly'failure' at this location(conversion to particulate debris)

2


–LTSBO–Nodalization1.S/RV2.Fuel rod Failure

1.Core Oxidation2.Damage function3.Failure model4.New input

3.Volatile FP speciation



10.MCCI


Vg# 12

Damage Function for Local Collapse of Fuel Rods

• Mechanical failure of fuel rods assumed to result from combination of:

– Loss of intact, unoxidized clad materal

– Thermal stress

• Molten Zr ‘breaks out’ from ZrO 2 shell at 2400 K

• Standing fuel rods collapse (forming particulate debris) based on a cumulative damage function

– Concept: Swelling, thermal expansion and mechanical stresses increase with temperature. Insults to fuel integrity build with time at temperature.







10.MCCI


Vg# 13

Fuel Degradation Modeling

• Molten metallic Zr breakout temperature (2400K)

• Fuel rod collapse– Time-at-temperature damage

function

– Similar to MAAP model

– Eliminates single temperature criterion

ZrO2 oxideShell

Oxidizing ZrMetal held underOxide shell

Release of Molten Zr (2400K)







10.MCCI


Vg# 14

Fuel Collapse Model Implementation

• The logic has been implemented within the code (MELCOR 2.1 & 1.8.6)

– Require new input records to activate the logic (set of CFs no longer needed)

– Different input format between two versions of the code

• Added input record: COR_ROD (CORROD in 1.8.6)

– Requires two fields• (1) IRODDAMAGE: tabular function name for the

residual lifetime of fuel as a function of cladding temperature (tabular function number (integer) in 1.8.6)

• (2) RCLADTHICKNESS: minimum un-oxdized clad thickness under which the rod collapse model supplants the default temperature based criterion (default = 1.0E-4 m)







10.MCCI


Vg# 15

The Phebus Experiment Facility

• Irradiated fuel heated in test package by Phebus driver core

– Fuel heatup

– Zr oxidation, H 2

– Fission product release

• Circuit (700 C) transports FP through steam generator tube

– Deposits in circuit and SG

• Containment receives FP gas and aerosol

– Settling

– Iodine chemistry

3



speciation–Phebus Facility–Validation–Vapor Pressures–FPT1 Deposition–Booth

Parameters

4.Structural aerosol5.Aerosol Deposition6.Debris HTF in LP7.RPV failure with


(Cavity)10.MCCI


Vg# 16

Validation of Fission Product Release Models

VERCORS 4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2000 4000 6000 8000 10000 12000

time (sec)

Rel

ease

Fra

ctio

n

0

500

1000

1500

2000

2500

3000

Tem

pera

ture

(K

)

ORNL-BoothdataCORSOR-MTemperature

VERCORS 4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2000 4000 6000 8000 10000 12000

time (sec)

Rel

ease

Fra

ctio

n

0

500

1000

1500

2000

2500

3000

Tem

pera

ture

ORNL BoothCORSOR MI dataCOR-TFU.102

VERCORS 4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2000 4000 6000 8000 10000 12000

time (sec)

Rel

ease

Fra

ctio

n

0

500

1000

1500

2000

2500

3000

Tem

pera

ture

(K

)

ORNL BoothCORSOR MTe dataTemperature

VERCORS 4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2000 4000 6000 8000 10000 12000

time (sec)

Rel

ease

Fra

ctio

n

0

500

1000

1500

2000

2500

3000

Tem

pera

ture

(K

)

ORNL BoothCORSOR MMo dataTemperature

Cs Release I Release

Te Release Mo Release

Temperature•Introduction•BWR



Parameters



(Cavity)10.MCCI


Vg# 17

Vapor Pressures of Some Important Species

• Molybdenum vapor pressure extremely low

• Cs2MoO4 considerably higher, but…

• Less volatile than CsOH or CsI

• MELCOR treatment– Cs and Mo treated as

Cs2MoO4 with respect to volatility

– CsI left unchanged

1000 1500 2000 2500 3000 35001 .10 4

1 .10 3

0.01

0.1

1

1010

0.0001

P Cs Ti( )atm

P CsI Ti( )atm

P CsMo Ti( )atm

P Mo Ti( )atm

3.5 103×1.025 103× Ti

K

Mo

Cs2MoO4

CsI

CsOH

fuelk

fuel

kv A

RT

P

D

Num )

0(

−

= D

&Vapor transport rate

vapo

r pr

essu

re -

atm

Temperature – K




Parameters



(Cavity)10.MCCI


Vg# 18

Cs Distribution as Fraction of Bundle Inventory: OR NL-Booth (modified)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

5000 7500 10000 12500 15000 17500 20000

time [sec]

frac

tion

of in

vent

ory

bundleplenumhot legsteam generatorcold legcontainmentTotal

- Plenum

- Hot Leg

- Stm Gen

- Containment

- total

FPT-1FinalDist

FPT-1 Deposition using Modified ORNL-Booth Release Model

• Distribution of transported fission products– Predictions versus experiment

– Performance reasonable for application




Parameters



(Cavity)10.MCCI


Vg# 19

CORSOR-Booth ORNL-Booth Adjusted

ORNL-Booth Diffusion coeff. D o 2.5x10-7 m2/sec 1x10-6 m2/sec 1x10-6 m2/sec

Activation Energy Q 3.814x105 joule/mole 3.814x105 joule/mole 3.814x105 joule/mole

Grain radius, a 6 µm 6 µm 6 µm Class Scale Factors --- --- ---

Class 1 (Xe) 1 1 1 Class 2 (Cs) 1 1 1 Class 3 (Ba) 3.3x10-3 4x10-4 4x10-4

Class 4 (I) 1 0.64 0.64 Class 5 (Te) 1 0.64 0.64 Class 6 (Ru) 1x10-4 4x10-4 0.0025 Class 7 (Mo) 0.001 0.0625 0.2 Class 8 (Ce) 3.34x10-5 4x10-8 4x10-8 Class 9 (La) 1x10-4 4x10-8 4x10-8 Class 10 (U) 1x10-4 3.6x10-7 3.2x10-4

Class 11 (Cd) 0.05 0.25 .25 Class 12 (Sn) 0.05 0.16 .16

Booth Parameters for Different Data Fits




Parameters



(Cavity)10.MCCI


Vg# 20

Release of Structural Aerosols

• For BWRs, principal source is tin (alloy material in Zircaloy)

– Approx. 70+ MT of Zircaloy in fuel clad + canister

– 1.45% of which is Sn

• Direct experimental measurements are very limited, but general observations from Phebus tests suggest:

– Sn levels greatly reduced in unoxidized Zr

– No Sn found in remnants of ZrO2

– Total quantity of Sn on downstream surfaces roughly half of total available mass



speciation4.Structural aerosol

–Background–Modeling

5.Aerosol Deposition6.Debris HTF in LP7.RPV failure with


(Cavity)10.MCCI


Vg# 21

Release of Structural Aerosols-- Modeling Approach (BWRs) --

• Create special RN class to track released mass separately from fission product Sn

• Invoke ‘non-fuel’ release model in COR Package

– Associate new RN class with releases from core components with Zr and ZrO 2

– Release rates scaled from CORSOR model for FP Sn

1

10

100

1000

10000

100000

0 1 2 3 4 5time (hr)

Mas

s [k

g]5

195

505

Sn as Fission Product

CORSOR-Booth

CORSOR-Booth

16,700

CORSOR-M

Sn from Zircaloy

CORSOR-M 34,600

Birchley FPT-1 multiplier

CORSOR multiplier = 1.0

2

CORSOR-Booth

CORSOR-M

3200%

1550%

47%

18%

ReleaseMass (kg)

Percent ofSn in Zirc

• Sensitivity calculations performed to determine appropriate release rate scalar

– Results for full-scale plant model compared to similar work by Birchley at PSI



speciation4.Structural aerosol

–Background–Modeling

5.Aerosol Deposition6.Debris HTF in LP7.RPV failure with


(Cavity)10.MCCI


Vg# 22

MELCOR Aerosol MechanicsMAEROS

• MAEROS sectional model of Gelbard– 10 sections [.1 - 50 µµµµm]– Condensed FP vapor sourced into

smallest section• Particles grow in size

– Agglomeration– Water condensation

• Particle fallout by gravitational settling• Particle deposition processes

– Thermophoresis– Diffusiophoresis– Brownian motion

• BWR structural aerosol release (Sn) from Zr cladding and canister

– Significant aerosol mass– Affects agglomeration, growth and

fallout• Cs chemisorption in RCS modeled

– Iodine from CsI revolatilizes when reheated

0.1 1 10 100

aerosol diameter [µm]

sect

ion

mas

s

0.1 1 10 100

aerosol diameter [µm]

sect

ion

mas

s

Aerosol size distribution evolves in time, depending on sources, agglomeration and removal processes

Time 1

Time 2



speciation4.Structural aerosol5.Aerosol Deposition

–MAEROS Aerosol mechanics

–Deposition–Pool Scrubbing

6.Debris HTF in LP7.RPV failure with


(Cavity)10.MCCI


Vg# 23

Aerosol Deposition on Reactor and Containment Surfa ces

• All deposition and retention mechanisms available in MELCOR are active in all regions of plant models

– Settling, phoretic processes, chemisorption, etc.• Special features added to address mechanisms not captured by

default models– “Filters” with filtration efficiencies designed to reflect:

• Impaction losses on elbows and surfaces of long-length piping upstream of rupture location in LOCAs

• Vapor scrubbing in water pools for species other than iodine

• Reactor, containment and auxiliary building surfaces are represented in detail

– High level of nodalization: proper temperature distributions and competing transport pathways

– Sub-divide complex structures into linked but separate surfaces to properly reflect orientation








(Cavity)10.MCCI


Vg# 24

Enhanced Pool Scrubbing Model

• Current SPARC90 pool scrubbing model – Fission product decontamination calculated

• aerosol Particles• currently, Iodine is the only vapor that is scrubbed

• Removal of CsOH and CsI vapors– Typically enter the pool at high temperature in vapor form– Would deposit on the bubble/water surfaces and be scrubbed– Cooling offered by the pool would condense the vapor species to

form aerosol particles– Treatment for the scrubbing of these vapor species now available

in MELCOR 1.8.6 and 2.1• Usage

– MELCOR 1.8.6: IBUBT or IBUBF field on FLnnn02 must be 2• e.g., FL10002 0 0 2 2

– MELCOR 2.1: ‘AllScrubbing’ (or 2) accepted as a vaild input for IBUBT or IBUBF on FL_JSW

• e.g., FL_JSW 0 AllScrubbing AllScrubbing








(Cavity)10.MCCI


Vg# 25

Debris Mass and Composition in Lower Head

0

20

40

60

80

100

120

140

160

180

10 15 20 25 30 35 40

time [hr]

Deb

ris M

ass

[MT

]

Failure of Lower Head

Failure of LowerCore Plate

UO2

ZrO2

Unoxidized steel

Zr

SS

0

20

40

60

80

100

120

140

160

180

15 15.5 16 16.5 17

time [hr]

Deb

ris M

ass

[MT

]

UO2

ZrO2

Zr

SS


– LTSBO– Nodalization1.S/RV2.Fuel rod Failure3.Volatile FP speciation4.Structural aerosol5.Aerosol Deposition6.Debris HTF in LP

–Debris mass in LH–Debris & LH

Temperatures–Falling debris

quench–Stable debris in LH–HT to LH

7.RPV failure with penetrations

8.H2 combustion9.Debris Spreading

(Cavity)10.MCCI


Vg# 26

Debris and Lower Head Temperature

500

700

900

1100

1300

1500

1700

1900

2100

2300

2500

10 15 20 25 30 35 40

time [hr]

Tem

pera

ture

[K]

Lower head dryout

Lower head wal l Inner surfaceOuter surface

Ring 1Early 'dribble' of Inconel

Lower core plate failure(bulk of core debris pours into lower head)

Creep rupture of hemispherical head

Debristemperature








(Cavity)10.MCCI


Vg# 27

MELCOR Framework for Debris-Coolant Heat Transfer i n Lower Head

• Step 1: “Falling Debris Quench”– Parametric model of fragmentation and cooling of a

molten jet pouring into pool of water

– Free parameters• Vfall (effective fall velocity)

• Heat transfer coefficient

• Dpart (Dh of final particles)

– Dpart and HTC developed from FARO data

– Vfall selected to mimic end-state temperature of debris in deep-pool FARO tests.








(Cavity)10.MCCI


Vg# 28

MELCOR Framework (continued)

• Step 2: Stable Debris Bed Heat Transfer

– Stable debris bed cooling limited by 1-D Lipinsky CCFL correlation

• Historically limited heat transfer to uppermost region of debris bed

– Coarse nodalization required to expose entire debris bed to water

• Proposed approach: restore detailed nodalization and disable1-D CCFL to reflect lateral in-flow of water from adjacent ‘rings’ of the debris bed.

– Permits calculation of debris temperature distribution

– Permits more accurate representation of heat transfer to control rod guide tubes

Top Guide &Upper tie plate

Lower tie plate& nose pieces

105

101

205

201

305

301

405

401

505

501

Hei

ght

of F

uel A

sse

mbl

ies

Hea

ted

Len

gth

Lower Core Plate &"Elephant's Foot"

Con

trol

rod

guid

es t

ube

s

BWR/4 Core Nodalization

106 206 306 406 506

117 217 317 417 517

104 204 304 404 504

103 203 303 403 503

102 202 302 402 502

108

208

308

408

508

107

207

307

407

507

109

209

309

409

509

110

210

310

410

510

111

211

311

411

511

112

212

312

412

512

113

213

313

413

513

114

214

314

414

514

115

215

315 41

5

515

116

216

316 416

516

Pen

etra

tion

- R

1

CRD stub tubes

Pe

netr

atio

n -

R2

Pe

netr

atio

n -

R3

Pen

etra

tion

- R

4

Pe

netr

atio

n -

R5

Lower head

TAF

BAF

0.0 m

3.086 m

3.619 m

4.152 m

4.685 m

5.218 m

5.494 m

5.875 m

6.256 m

6.637 m

7.018 m

7.399 m

7.780 m

8.161 m

8.542 m

8.923 m

9.304 m

9.669 m








(Cavity)10.MCCI


Vg# 29

MELCOR Framework (concluded)

• Step 3: Heat Transfer to (and failure of) Lower Head

– New 2-D curved head model in MELCOR 1.8.6

– Solid debris heat conduction to vessel wall

– Heat transfer coefficient between debris & head sensitive to debris temperature and morphology

– Creep rupture of hemispherical head based on Larson-Miller parameter and life-fraction rule applied to a 1-D mechanical model








(Cavity)10.MCCI


Vg# 30

Effect of Penetrations on Failure Criteria

• Penetration failure can be represented with the following tools:– Failure criteria specified via user-defined control function

– Distinct temperature of lumped parameter steel mass in contact with debris and inner surface of lower head




penetrations–Modeling–Justification


(Cavity)10.MCCI


Vg# 31

Baseline Analyses will Not Exercise Penetration Fai lure Model

• Reasons:

– Experimental/analytical work for BWR penetrations does not conclusively demonstrate high probability of failure at a time that significantly precedes creep rupture of the head

– Melt penetration into penetration/stub tube structure does not necessarily result in debris ejection from RPV

– Lumped-parameter penetration model in MELCOR does not account for complexities of melt penetration into structure and local changes in debris state

– MELCOR sensitivity studies with active model (using reasonable range of

penetration masses)indicate penetration failure has small impact on event chronology




penetrations–Modeling–Justification


(Cavity)10.MCCI


Vg# 32

Hydrogen Combustion & Ignition

• MELCOR (HECTR) combustion models will be active in all calculations

– Apply default criteria for steam inerting, combustion efficiency, flame speed, etc.

– One non-default option: • Time required for a flame to propagate to neighboring

control volume specified on an individual CV basis

• Ignition criteria

– Use default for sequences with well-defined ignition sources (generally all cases with active ac power)

– Defer ignition until vessel breach for total loss of power scenarios.





(Cavity)10.MCCI


Vg# 33

Lateral Debris Spreading in Mark I Drywell

• Potential for early drywell failure often dominated by drywell shell melt-through in Mark I containment

– Not a factor in some Mark I plants due to deep sumps or curbs

• Modeling approach follows basic conclusions of NRC issue resolution

– Potential for failure dominated by lateral debris mobility





(Cavity)–Mark I drywell–Debris spreading–Contact with

drywell liner

10.MCCI


Vg# 34

Debris Spreading / Shell Melt-through Criteria

• Debris mobility tied to debris temperature and static head (height differential between neighboring areas):

– Overflow not allowed if Tdebris < Tsolidus

– Above solidus:• CAV0 to CAV1: 0.5 m when Tdebris > Tsolidus

0.15 m when Tdebris = Tliquidus

• CAV1 to CAV2: 0.5 m when Tdebris > Tsolidus

0.10 m when Tdebris = Tliquidus

• Spreading rate expressed in terms of transittime across single CAV

– When Tdebris = Tliquidus: 10 min for CAV130 min for CAV2

– When Tdebris = Tsolidus: infinite

• 5 min delay to shell failure after debris contact with T > 1811 K






drywell liner

10.MCCI


Vg# 35

Debris Spreading & Contact with DW Liner

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

20 30 40 50

time [hr]

Deb

ris D

epth

[m]

In-pedestal(CAV 0)

90o sector outside pedestal doorway

(CAV 1)

Balance of drywell floor (CAV 2)

CAV 2CAV 1CAV 0

0

500

1000

1500

2000

2500

20 30 40 50

time [hr]

Tem

pera

ture

[K]

In-pedestal (CAV 0)

90o sector outside pedestal doorway

(CAV 1)

Balance of drywellfloor (CAV 2)

T-ablation(1750K)

(S)

(L)

Time delay between Vessel Breach and DW

melt-through:14 min






drywell liner

10.MCCI


Vg# 36

Coriu m Cru st to W ater Hea t F lu x

0

5 00

10 00

15 00

20 00

25 00

30 00

35 00

40 00

45 00

50 00

0 0 .1 0.2 0 .3 0 .4 0 .5

T im e (h r )

Hea

t Flu

x (k

W/m

**2)

1*K2*K

5*K10 *K

20 *K50 *K

10 0*K

MCCI Modeling

• Corium assumed to be well mixed (default)

• Enhanced effective corium thermal conductivity (10x)

– produces 1 to 5 MW/m2

heat flux

– Accounts for cracks and fissures and crust failure

– Consistent with interpretation of MACE tests

d d

concrete

corium

water

Range observed In MACE Tests

δδδδδδδδ





(Cavity)10.MCCI


Vg# 37

Summary of Main Points for PWR Discussion

• Pump seal leakage and blowout• RCS natural circulation treatment• Core plate failure

•Introduction•BWR•PWR

– Nodalization– SBO1.Pump seals2.RCS natural

circulation 3.Core plate

failure

•Other Best Practices

• Safety relief valve cycling and failure• Fission product release, speciation, and volatility• Fuel degradation and relocation treatment• Debris/coolant heat transfer• Vessel head failure and debris ejection• Hydrogen combustion• MCCI

Issues Specific to PWR reactors

Issues Previously discussed (Treated the Same as for BWR reactors)

Vg# 38

Plant and NSS Nodalizations

• Plant Buildings– Containment

• Elevation View

• Aerial view

– Other Buildings

• Detailed nodalizations of RCS and Core

– Capture important 2-D effects

– Natural circulation patterns

• Core

• RCS

• Steam generators

• Loop seals




failure


Vg# 39

Walkthrough of Station Blackout Accident in a PWR

• Short term station blackout

• Loss of ac power

• No feedwater injection

• No ECCS

• Leaking pump seals

• Key modeling issues identified in walkthrough


– Nodalization– SBO

• SBO definition• Initiation to SG

dryout• SG dryout• SG dryout to

pump seal failure

• Core uncovery to hotleg failure

• Core Waterlevel

1.Pump seals2.RCS natural

circulation 3.Core plate failure


Vg# 40

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7 8

Time (hr)

Pre

ssur

e (M

Pa)

PressurizerSG ASG CSG B

Hot leg C creep rupture

SG dryout

Station Blackout High Pressure PWR SequenceAccident Initiation – SG dryout

• Initial full loop RCS water circulation removes energy

• Main coolant pump seals leak water

• Pressurizer safety valve cycling stops





pump seal failure


• Core Waterlevel




Vg# 41

Steam Generator Secondary WaterAccident Initiation – SG dryout

• Full loop RCS natural circulation period

• Good decay heat removal

• Secondary dry at ~1.2 hr

• Primary RCS pressurization follows

SG Downcomer LevelsSTSBO

0

2

4

6

8

10

12

14

0 0.5 1 1.5 2 2.5 3

Time (hr)

Leve

l (m

)

SG ASG BSG C

Bottom of the downcomer





pump seal failure


• Core Waterlevel




Vg# 42

Station Blackout High Pressure PWR SequenceSG dryout – Pump Seal Failure

• SG dryout starts RCS re-pressurization to relief valve setpoint• RCS becomes steam-filled challenging pump seals

– Seal blowout at 2.8 hrs• Seal failure increases coolant mass loss rate• Cycling relief valve

– Same treatment as BWR SRV

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7 8

Time (hr)

Pre

ssur

e (M

Pa)



SG dryout

pump sealfailure leads todepressurizationcycling

reliefvalve

PumpSeal

failure





pump seal failure


• Core Waterlevel




Vg# 43

Station Blackout High Pressure PWR SequenceCore Uncovery – Hotleg failure

• Coolant loss and low core water level leads to RCS depressurization

• Core damage phase

• PWR valves less susceptible to high temperature conditions

Primary and Secondary PressuresSTSBO - No Mitigation

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7 8

Time (hr)

Pre

ssur

e (M

Pa)



SG dryout

pump seal failure leads todepressurization

PumpSeal

failure





pump seal failure


• Core Waterlevel




Vg# 44

Core Water Level

• Hot leg and SG natural circulation• Hot leg failure depressurizes vessel

– Accumulators dump• Partial core quench and second vessel boildown• Core damage and hydrogen generation as water in core falls

Vessel Water LevelSTSBO

-4

-2

0

2

4

6

8

10

0 1 2 3 4 5 6 7 8

Time (hr)

Tw

o-P

hase

Lev

el (

m)

Accumulators

BAF

TAF

Lower head

Vessel top

Vessel failure





pump seal failure


• Core Waterlevel




Vg# 45

Seal LeakageSTSBO - No Mitigation

0

20

40

60

80

100

120

140

160

180

0 1 2 3 4 5 6 7 8

Time (hr)

Flo

w R

ate

(gpm

)

Total Seal LeakageSeals fail

Pump Seal Leakage

• Model based on Rhodes analysis of leakage and likelihood and degree of seal failure

– Seals initially leak on loss of site power and back pressure• 21 GPM

– Saturation conditions in RCS (high temperature) produces seal failure• Failure can range between 170 and 250 GPM

• Assume:– 21 GPM initially– 170 GPM at saturation




failure


Vg# 46

Natural Circulation Modeling

• SCDAP/RELAP5 Studies from mid-1980’s to present

• COMMIX CFD, 1987

• 1/7th-Scale Westinghouse Test, 1989-1993

• Fluent CFD Work, 2003 to present– Numerical CFD extends work

• 1/7th-scale

• Full-scale

• Westinghouse designs

• CE designs

• SCDAP/RELAP5 SGTI analysis– FLUENT support



circulation 1.Background2.Assessment3.MELCOR

modeling4.Hotleg

modeling5.Tube flow

modeling6.Other

modeling considerations

3.Core plate failure


Vg# 47

• 1/7th Westinghouse Assessment

– Steady state tests

– Safety valve cycles

– Hot leg fission product heating

– Hydrogen binding

• Comparison to experiment and SCDAP/RELAP5 (where available)

– In-vessel

– Hot leg

– Steam generator

Natural Circulation ModelingMELCOR Approach




modeling4.Hotleg

modeling5.Tube flow

modeling6.Other




Vg# 48

• MELCOR vessel and RCS models developed from SCDAP/RELAP5 natural circulation models

– 5 ring vessel with 2-D core and upper plenum

– Geometry and loss factors from RCS

– Zion, Surry, and Calvert Cliffs SCDAP/RELAP5 models

– New modeling approach to hot leg and steam generator natural circulation flows

• SCDAP/RELAP5 renodalizes model when natural circulation conditions are expected

– Special 2-D hot leg and steam generator model

• Application of MELCOR includes calculation of source term beyond RCS failure

– S/R5 used to predict timing and location of creep rupture failure and not subsequent events

Natural Circulation ModelingMELCOR Approach4




modeling4.Hotleg

modeling5.Tube flow

modeling6.Other




Vg# 49

• Hot leg counter-current natural circulation tuned to a Froude Number correlation using results from FLUENT CFD analysis

where

g acceleration due to gravity.

Q volumetric flow rate in a horizontal duct

ρρρρ average fluid density (ρ)

∆ρdensity difference between the two fluids

CDhot leg discharge coefficient





modeling4.Hotleg

modeling5.Tube flow

modeling6.Other




Vg# 50

• Steam generator tube to hot leg flow ratio tuned results from the FLUENT CFD analysis

• Inlet plenum subdivided into 3 regions for hot, mixed, and cold regions from plume analyses

• Steam generator mixing fractions based on FLUENT CFD analysis

– M-ratio(steam generator tube to hot leg flow ratio) = 2





modeling4.Hotleg

modeling5.Tube flow

modeling6.Other




Vg# 51

• Explicit modeling of structures in hot leg and steam generator– Convective heat transfer

• Augmented in hot leg based on FLUENT turbulence evaluations

– Gas to structure radiative exchange in the hot leg and steam generator

– Ambient heat loss through the piping and insulation

• Individual modeling of relief valves– When the valves are lumped, it creates a very large flow that

non-physically disrupts natural circulation flow patterns and the timing of the valve openings

• Creep rupture modeling– Hot leg nozzle carbon safe zone

– Hot leg piping

– Surge line

– Steam generator inlet tubes





modeling4.Hotleg

modeling5.Tube flow

modeling6.Other




Vg# 52

Westinghouse PWR Core Plate

• Weight of core material mass• Engineering stress formulae used (e.g.

Roark)• Failure based on exceeding yield stress at

temperature• Sequential failure of multiple supporting

structures treated

CL

Lower core plate

Flow mixer plate

Core plate Support Columns

1

Level

5

4

3

2

1

6

Ring 2 3 4 5

PLATEG (Level 6)

PLATEG (Level 5)

COLUMN (Level 4)

PLATE (Level 3)

Lower core plate

Flow diffuser plate

Core plate support columns

Core support forging




failure


Vg# 53

Other MELCOR Best Practices

• Some standardize some non-default input– Porosity of particulate debris

• CORZjj01 PORDP 0.4

• Some Numeric in Nature– SC-4401(3); Maximum number of iterations permitted

before solution is repeated with a decreased (subcycle) timestep.

• Some enable some previously non-default models– RN1002 – enable Hygroscopic model– FLnnnFF – KFLSH=1 enables flashing model

• Some new models activated– FLnnn02 IBUBF & IBUBT

• -1 Vapor heat transfer in pools for RCS FLs• +2 SPARC scrubbing in pools for spargers, quencher,

vents, and BWR downcomers.


– Nodalization– SBO1.Pump seals2.Loop seal 3.RCS natural


failure


– Overview– Default

Templates– Tables 1– Tables 2– Tables 3– Tables 4– Tables 5– Tables 6– Tables 7– Tables 8– Tables 9– Tables 10

Vg# 54

MELCOR Default Templates

! The following records updates the default by individual packageCOR_DFT 1.86COR_DFT 1.86COR_DFT 1.86COR_DFT 1.86CAV_DFT 1.86CAV_DFT 1.86CAV_DFT 1.86CAV_DFT 1.86RN1_DFT 1.86RN1_DFT 1.86RN1_DFT 1.86RN1_DFT 1.86HS_DFT 1.86HS_DFT 1.86HS_DFT 1.86HS_DFT 1.86CVH_DFT 1.86CVH_DFT 1.86CVH_DFT 1.86CVH_DFT 1.86

! This record restore ! This record restore ! This record restore ! This record restore original defaults all at original defaults all at original defaults all at original defaults all at onceonceonceonceEXEC_GLOBAL_DFT 1.86EXEC_GLOBAL_DFT 1.86EXEC_GLOBAL_DFT 1.86EXEC_GLOBAL_DFT 1.86

• New defaults enabled automatically in 2.1

• M1.8.6 defaults enabled as follows:

! The following records ! The following records ! The following records ! The following records updates the default by updates the default by updates the default by updates the default by individual packageindividual packageindividual packageindividual packageCORDEFAULT 2.0CORDEFAULT 2.0CORDEFAULT 2.0CORDEFAULT 2.0CAVDEFAULT 2.0CAVDEFAULT 2.0CAVDEFAULT 2.0CAVDEFAULT 2.0RN1DEFAULT 2.0RN1DEFAULT 2.0RN1DEFAULT 2.0RN1DEFAULT 2.0HSDEFAULT 2.0HSDEFAULT 2.0HSDEFAULT 2.0HSDEFAULT 2.0CVHDEFAULT 2.0CVHDEFAULT 2.0CVHDEFAULT 2.0CVHDEFAULT 2.0

! This record restore ! This record restore ! This record restore ! This record restore updates the default all updates the default all updates the default all updates the default all at onceat onceat onceat onceDEFAULT 2.0DEFAULT 2.0DEFAULT 2.0DEFAULT 2.0

• New defaults disabled automatically in 1.8.6

• M2.1 defaults enabled as follows:

Note: See User Guide for list of those default items changed in M2.0 default template




failure




Vg# 55

Other Common Best Practices

Item Record Field Value(s) Description

1. BUR000 IACTV 0 (Active) Burn package activation

2. BUR1xx

(xx = CV)

IGNTR 86 for CVs where ignition is to be prohibited.

Apply to RCS control volumes to preclude combustion.

3. BUR1xx

(xx = CV)

TFRAC 1.0 Time fraction of burn before propagation to neighboring CV is allowed. Value of 1.0 means a flame must travel the radius of the control volume before propagating to its neighbor.

4. FLnnn0T ZBJT0,

ZTJT0

ZTJT0 = ZBJT0 + ∆∆∆∆z

(For axial containment flow paths only)

To insure that MELCOR properly estimates vertical burn propagation in containment, drywell, reactor building, and auxiliary building, it is necessary to define “vertical” flow path “from” and “to” elevations with a small dZ. If the “from” and “to” elevations are set equal (which has been historical practice to ensure complete vertical pool drainage), the MELCOR burn package uses criteria for horizontal burn propagation.

5. FLnnnFF KFLSH 1 Calculate superheated pool flashing for all liquid LOCA connections to initially dry containment regions. KFLSH activates the model. Activate RN1Ikkk as needed for impact into specified heat structures.

6. FLnnn02 IBUBF & IBUBT -1

+2

Vapor heat transfer in pools for RCS FLs.

SPARC scrubbing in pools for spargers, quencher, vents, and BWR downcomers.

7. RN2FLTXX00 FPVAPOR Various geometric values MELCOR SPARC pool scrubbing model was modified to scrub all gaseous RN classes for

8. COR00001 DRGAP 0.0 Thickness of gas gap between fuel pellets and cladding set 0.0 to account for swelling of operating fuel.

9. COR00001A ILHTYP

ILHTRN

0

BWR =0, PWR =1

Lower head is a hemisphere

Transition is at RCOR (BWR)

or RVES (PWR)




failure




Vg# 56



10. COR00009 HDBPN

HDBLH

MDHMPO

MDHMPM

TPFAIL

CDISPN

100 W/m2-K

100 W/m2-K

‘MODEL’

‘MODEL’

9999 K

1.0

This record activates the internal molten pool to lower head heat transfer models and provides reasonable solid debris to lower head heat transfer coefficient.

11. COR00012 HDBH2O

VFALL

2000 W/m2-K

0.01 m/s

HTC in-vessel falling debris to pool (W/m2-K)

Velocity of falling debris (m/s). ). Perhaps not correct for shallow pools and not necessary in deep pools since adoption of no 1-D CCFL limitation via the one-dimensional Lipinski model.

12. CORCR0 IAICON 2 For PWRs only

Activate control rod release model, 2 = Model is active, vaporization is allowed from both candling material and conglomerate.

13. CORZjj01 PORDP 0.4 Porosity of particulate debris

14. CORijj04 DHYPD Core - 0.01 m

LP - 0.002 m

Particulate debris equivalent diameter (LP values for DHYPD, HDBH2O, VFALL tuned to get appropriate end-of-pour debris temperature. 2mm based on FAERO fragmented debris size). Perhaps not correct for shallow pools.

15. CORZjjNS TNSMAX 1520 K

1700 K

Control blades failure temperature (BWR)

Core top guide failure temperature (BWR)




failure




Vg# 57



16. CORijjDX FBYXSS Calculated. For BWRs only. Fraction of lower head COR cells normally displaced by control rod guide tubes should be ‘excluded’ from volume available to particulate debris. Volume recovered when tubes (as supporting structure) fails.

17. SC-1131(2) TRDFAI 2800 K Fuel rod collapse temperature (addressed with CORijjFCL records)

18. SC-1141 (2) GAMBRK 0.20 kg/m-s Molten Zr breakout flowrate parameter to yield 2 mm/s as evidenced in CORA experiments

19. SC-1701 (1) 0.01 Open volume fraction for subnode blockage criterion. This is the default setting.

20. SC-4401(3) XPASMX 15 Maximum number of iterations permitted before solution is repeated with a decreased (subcycle) timestep.

21. DCHNEMnn00 ELMNAM

ELMMAS

Use ORIGEN results for core, if available.

Elemental fission product mass at shutdown for calculation of decay heat.




failure




Vg# 58



22. DCHNEMnnmm DCHEAT Use pre-combined methodology for Cs, I, and

Mo

Elemental fission product decay heat per unit mass (based on shutdown RN inventory).

•Define specific decay heat for CsI (Class 16) as 0.51155 of value for Class 2 (Cs) plus 0.48845 of value for Class 4 (I).

•Define specific decay heat for Cs2MoO4 (Class 17) as 0.7348 of value for Class 2 (Cs) plus 0.2652 of value for Class 7 (Mo).

If ORIGEN results are not available for the core, perform an input deck with BE burn-up and cycle history. Redistribute RN mass as follows,

•Class 2 initial mass represents the NUREG-1465 Cs gap mass not already included in Class 16.

•Class 4 initial mass is empty (10-6 kg)

•Class 7 initial mass is remaining Mo mass not included in Class 17.

•Class 16 has all I and an appropriate amount of Cs mass for CsI stoichiometry.

•Class 17 has the remaining Cs not included in Classes 2 and 16 plus Mo for Cs2MoO4 stochiometry.

23. DCHCLSnnn0,

DCHCLSnnnm

RDCNAM,

CLSELM

New RN

definitions for

Classes 1-12, 16-18

If ORIGEN results are available, synthesize ORIGEN data to define a single representative element for each class with decay heat data that reflects decay heat for all elements within the class (DCHNEMxxxx input.) Redefine each class to include only the representative element.




failure




Vg# 59



24. DCHDEFCLS0 DEFCLS 13, 14, 15 Specifies that MELCOR DCH default classes are to be used.

25. DCHCLNORM CLSNRM ‘No’ when ORIGEN results are available.

‘Yes’ when MELCOR is used to estimate initial inventories.

New ORIGEN input for elements/classes defines the total core decay heat.

Otherwise, let MELCOR normalize the elemental decay heats to the rated power.

Do not use RN1DCHNORM. Default behavior normalizes Class 10 (Uranium).

26. HSccccc400 &

HSccccc600

CPFPL

CPFAL

See discussion Minimum value of CVH pool fraction such that heat transfer is calculated to Pool/Atmosphere. For heat structures within the RPV, use 0.9. For PWR SG Tubes, use 0.1. All other structures modeled use default value of 0.5.

27. HSccccc401

HSccccc601

EMISWL

RMODL

PATHL

0.27

EQUIV-BAND

0.1 m

Mean emissivity of SS type 316

Equivalent band radiation model.

Nominal optical distance in steam (m).

For SS heat structures within the reactor vessel and those being monitored for creep-rupture failure.

28. HSDGccccc0 ISRCHS

ISDIST

GASNAM

HS #

1

SS

Heat structure for application of degas model.

Degassing model requires 1 mesh.

Name of released gas.

For SS boundary structures modeled with the HS package that are coupled to the core.




failure




Vg# 60



29. HSDGccccc1 RHOSRC

HTRSRC

TEMPL

TEMPU

7930 kg/m3

2.68x105 J/kg

1695 K

1705 K

Gas source density.

Gas source heat of reaction.

Lower temperature for degassing.

Upper temperature for degassing.

For SS boundary structures modeled with the HS package that are coupled to the core.

30. MPMATxxxx MLT 2800 K

2800 K

Uranium-dioxide

Zirconium-oxide

Because of the interactions between materials, liquefaction can occur at temperatures significantly below the melt point. The interaction between ZrO2 and UO2 results in a mixture that is fluid at above about 2800 K (compared to the melting temperatures of

3113 K and 2990 K, respectively, for the pure materials). Similarly, although pure B4C melts

at 2620 K, interaction with steel produces a mixture that is fluid at above about 1700 K.

31. RN1001 NUMSEC

NUMCMP

NUMCLS

10

2

20 (PWR)18 (BWR)

Default

Default

For BWR & PWR: 16 = CsI, 17 = Cs2MoO4

Now Class 17 includes default settings for Cs2MoO4.




failure




Vg# 61



32. BWR structural tin release RN/DCH data for RN Class 18

For BWR: RN Class 18 = SnO2 (non-radioactive)

Define SnO2 (DCHCLSnnn0)

18 = ‘SnO2’

SnO2decay heats (DCHNEMnn00)

0 W/kg (no decay heat)

SC(7110) vapor pressures

SnO2: Log10(P(mm Hg)) = 15400/T + 8.15

SC(7111) diffusion coefficients

SnO2: Sigma = 3.617, E/K = 97

SC(7120) elem./compound molecular weights

Sn: MW = 150.7 kg/kg-mole




failure




Vg# 62



33. PWR control rod RN data for RN Classes 18, 19, and 20

For PWR RN Class 18 = Ag, 19 = In, 20 = CdDefine Ag, In, Cd (DCHCLSnnn0)

18 = ‘Ag-CR’, 19 = ‘In-CR’, 20 = ‘Cd-CR’

Ag, In, Cd decay heats (DCHNEMnn00)

0 W/kg (no decay heat)

SC(7110) vapor pressures

Ag: Log10(P(mm Hg)) = 1000/T + 1.26x104 + 7.989

In: Log 10(P(mm Hg)) = 400/T + 1.27x105 + 8.284

Cd: Log10(P(mm Hg)) = 500/T + 5.31x103 + 7.99

SC(7111) diffusion coefficients

Ag: Sigma = 3.48, E/K = 1300

In: Sigma = 3.61, E/K = 2160

Cd: Sigma = 3.46, E/K = 1760

SC(7120) elem./compound molecular weights

Ag: MW = 107.8 kg/kg-mole

In: MW = 114.8 kg/kg-mole

Cd: MW = 112.4 kg/kg-mole

34. RNCA100 ICAON 1 (Active) Chemisorption model is active (default).

35. RN1002 IHYGRO 1 (Active) Hygroscopic model activation. (RNACOND set to default, 0 = condensation of water onto all aerosols.)




failure




Vg# 63



36. RNCRCLxx

SC7100

ICRMT / ICLSS / FRAC

(2) Zr

(3) ZrO2

(4) steel

(5) steel ox.

(6) B4C

2 / 18 / 0.0145

3 / 18 / 0.0145

0.1

1.0

0.0

0.0

0.0

For BWRs, apply the non-fuel release model. Assign aerosol generated from Zr and ZrO 2 to RN Class 18 (SnO2). The mass will be added as a non-radioactive mass to this class. The fraction of material mass available for release as an aerosol from these materials is 0.0145 (Sn fraction in Zirc-2 and -4.)

Note: must also add input for the release rate (SC7103) for RN Class 18. Values should be identical to those used (default) for Class 12 (fission product Sn).

Multipliers for various structural material types

37. RNFPNijjXX NINP

RINP1

RINP2

Use ORIGEN results, if available.

NINP = RN Class, RINP1 = mass, RINP2 = axial peaking factor. Distributes mass based on distribution developed with ORIGEN.

If ORIGEN results are unavailable, NINP = 0, RINP1 = axial peaking factor, RINP1 = radial peaking factor. Where,

ΣΣΣΣiΣΣΣΣj RINP1 * RINP2 = 1.




failure




Vg# 64



38. RNGAPijjnn NINP

RINP1

RINP2

1 (Xe) = 0.05

2 (Cs) = 1.00

3 (Ba) = 0.01

5 (Te) = 0.05

16 (CsI) = 0.05

Where, NUREG-1465 recommends the following gap quantities,

•Xe = 5%

•Cs = 5%

•Ba = 1%

•Te = 5%

39. RN2FLTXX00 FPVAPOR Various geometric values For all flow paths entering pools via quenchers or spargers, specify the flow path to scrub all gaseous RN classes.




failure




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