nrc-ge meeting 03-08-06-confirmatory melcor analysis of … · 2012. 11. 21. · fl812 fl813 fl814...

ERIEnergy Research, Inc.

CONFIRMATORY MELCOR CONFIRMATORY MELCOR ANALYSIS OF SEVERE ACCIDENTS ANALYSIS OF SEVERE ACCIDENTS

FOR ESBWRFOR ESBWR

by:by:Z. Yuan, M. Zavisca, A. Krall and M. KhatibZ. Yuan, M. Zavisca, A. Krall and M. Khatib--RahbarRahbar

Energy Research, Inc.Energy Research, Inc.6167 Executive Blvd.6167 Executive Blvd.

Rockville, Maryland 20852Rockville, Maryland 20852

U. S. Nuclear Regulatory Commission Meeting With General Electric Company On ESBWR Severe Accident Sequences and

Thermal-Hydraulic Uncertainties

March 8, 2006

2


OUTLINEOUTLINEObjective of the NRC MELCOR analysesMELCOR Modeling of ESBWR

• Nodalization• Other modeling aspects• StatusPre-Accident Initialization/Steady-State

3


OUTLINE (Cont.)OUTLINE (Cont.)

Results of Preliminary Calculations• Accident Scenario• Simulated Cases

Case 1: With MCCI! Lower Head Sensitivity Calculations

Case 2: Without MCCI

Remaining Data NeedsList of Plant Calculations

4


OBJECTIVESOBJECTIVESTo support the design certification review of severe accident risk by NRC in

Independent assessment of severe accident responseConfirmatory assessment of representative radiological release estimatesDevelopment of uncertainties in the initial and boundary conditions for analysis of selected severe accident issues (e.g., ex-vessel steam explosion)

5


MELCOR Model DevelopmentMELCOR Model DevelopmentDeveloped initial input deck for MELCOR 1.8.6 using GE design data (November 18, 2005)This deck subjected to an independent QA and review Due to problems with MELCOR 1.8.6, model was converted to MELCOR 1.8.5 and revised based on QA & review comments.Plan to perform limited calculations for ESBWR using MELCOR 1.8.6 when the code is ready.

6


MELCOR Model Development (Cont)MELCOR Model Development (Cont)Deck conversion to MELCOR 1.8.5:

Flat-bottom RPV instead of the new hemispherical LHMinor changes to core nodalization (to enhance running time)Minor changes to the suppression pool (water) nodalization in response to QA & review commentsUpdated design data based on MFN05-142, 06-003, 06-009, 06-029

7


CORE/RPV NODALIZATIONCORE/RPV NODALIZATION• The core nodalization:

5 radial rings, 13 axial levels (9 for active fuel, 1 above top of active fuel, 1 between bottom of active fuel & top of the core plate, 2 in the lower plenum).

• Separate Control Volumes (CV) used for each ring, heated channels and the bypass regions• 1 CV used for every 3 axial levels of active fuel region, plus

another level of CV for regions above the active fuel.• As a result, a total of 25 CVs for the core (4 levels x 5 rings

for the core channels plus 5 for the bypass).

8


101102103104105

106

107

108

109

110

111

112

113

114

115

116

117

118

Ring 1 Ring 2 Ring 3 Ring 4 Ring 5

Low

er P

lenu

mA

ctiv

e Fu

el

Core Plate

CV135

CV134

CV133

CV132

CV131

CV120

Upper Core Structure (e.g., top guides)

Cor

e Sh

roud

RPV Lower Head

ORIGINAL MELCOR

1.8.6 Model

9


101

102

103

104

105

106

107

108

109

110

111

112

113

Ring 1 Ring 2 Ring 3 Ring 4 Ring 5

Low

er P

lenu

mA

ctiv

e Fu

el

Core Plate

CV134

CV133

CV132

CV131

CV120

Upper Core Structure (e.g., top guides)

RPV Lower Head

LATEST MELCOR

1.8.5 Model

10


CORE/RPV NODALIZATION (Cont.)CORE/RPV NODALIZATION (Cont.)• Other CVs used inside RPV to represent:

• Lower plenum;• Separators (inside volume of the steam separators) and mixing

plenum/partitioned chimney;• Dryers and steam dome region;• Separator return to upper downcomer, combined with the liquid

drain area outside the steam separators; and• Lower downcomer.

• 2 CVs used to represent 4 main steam lines (1 CV for one of the lines, and 1 CV combines the remaining 3 lines, allowing simulation of a break in one line).

• Feed water system has been modeled (using external mass and energy sources in the CV package and CFs)

11


Dryer / Steam Dome

Sepa

rato

r Ret

urn

to

Upp

er D

ownc

omer

Separators /Chimney Plenum

Chimney Partition

Core / Bypass

Lower Plenum

Low

er D

ownc

omer

190

134

180185

1xx 2xx

120

110

139

149

159

169

179

191

180

185139 149 159 169 179

11014

4

154

164

174

134 234 144 244 154 254 164 264 174 274

334 344 354 364 374

133

143

153

163

173

133

143

153

163

173

333 343 353 363 373

132

142

152

162

172

132

142

152

162

172

332 342 352 362 372336 346 356 366

131

141

151

161

171

131

231

141

241

151

251

161

261

171

271

331 341 351 361 371

130 230 140 240 150 250 160 260 170 270

FeedwaterInlet

190

12


CONTAINMENT NODALIZATIONCONTAINMENT NODALIZATION• Each of the 4 divisions of the 3 GDCS pools is

represented individually (also modeled the 2 divisions existing for GDCS #2). One CV used for each of 3 GDCS pools, along with controlled flow paths for injection, equalization & deluge lines.

• 6 units of PCCS are represented by 2 sets of CVs & FLs. (1 single & 5 combined).

• 4 units of IC are represented by 2 sets of CVs (1 single & 3 combined).

13


CONTAINMENT NODALIZATION (Cont)CONTAINMENT NODALIZATION (Cont)

• PCCS & IC modeled mechanistically• Condensation and drainage of water inside

tubes modeled inside the MELCOR HS package, using a film tracking network.

• PCCS and IC inlet lines modeled as CVs and HSs.

• Heat transfer from drywell (upper head) to the “reactor well” water is included.

14


Lower Drywell

Lower Plenum

Dow

ncom

er

Core / Bypass

Chimney Partition

Separators /Chimney Plenum

Dryer / Steam Dome

Wetwell

GDCS-1MSL

MSL

Turb

ine

Build

ing

Drywell Head

IC Pool

PCCS Pool IC-1 IC-2/3/4 PCCS Pool

Envi

ronm

ent

GDCS-2 GDCS-3

Dry

wel

l Shi

eldw

all A

nnul

us

Upp

er D

ryw

ell

DW

Dow

ncom

er

Vent

Wetwell

400

120

190

180

110

185

524524

522

610

195

196

198

430

420

410

900

620 630

440

515

511

512

513514

521

522

523524

810

817

816815814813812811

710

717

716715714713712711

720

727

726725724723722721

820

827

826825824823822821

FL51

5FL

514

FL51

3FL

512

FL554

FL553

FL552

FL551

FL52

5FL

524

FL52

3FL

522

FL441

FL451

FL461

FL440

FL411 (vacuum break)

FL895

FL728

FL829

FL631

FL633

FL630 FL632FL622

FL620

FL621

FL623

FL820FL810

FL410

FL415

FL495(DPV)

FL100 (FW in)

FL400

FL420

FL729

FL720

FL199 (VB)

FL198 (BDL)

850

FL719

FL710

FL718FL819

FL818

FL593(Eq. Line)

FL193

FL194

FL590(break to CV410)

FL195

FL196

FL592

FL591

FL613

FL612(from

CV410)

FL811FL812

FL813

FL814

FL815

FL816

FL817

FL711FL712

FL713

FL714

FL715

FL716

FL717

FL721FL722

FL723

FL724

F725

FL726

FL727

FL821FL822

FL823

FL824

FL825

FL826

FL827

FL611

FL614(from GDCS-1)

FL615(from GDCS-1)

Dry

/ S

epar

ator

Sto

rage

Tan

k

890

750

850

FL795

FL890FL890

FL901FL902

FL632

Mid

dle

Dry

wel

l

405

FL412

FL418(Leakage)

FL498(Normal Containment

Leakage)

FL629FL594(Eq. LineBreak)

Reactor Well 892FL

809

FL83

9 FL494(CIS)

FL499(Cont.Rupture)

809

819

15


OTHER MODELING ASPECTSOTHER MODELING ASPECTS• Containment spray system and venting system

have been included (noting that the missing design data need to be requested from GE).

• Refill of PCC/IC pool is included via a control function to maintain coverage of PCCS tubes.

• BiMAC system has not been explicitly modeled (the intended impact of BiMAC may be investigated through a parametric representation within MELCOR; otherwise, specific design information may be required).

16


STATUSSTATUS

• All aspects of the model, peer review and QA comments have been documented.

• NRC staff have been involved in all aspects of this work (including direct involvement in steady-state calculations).

17


STATUS (Cont.)STATUS (Cont.)• A complete 1.8.5 model is available and

initial confirmatory calculations are underway.• Results of a representative accident scenario with

limited comparisons to the GE submittal completed (not yet documented).

• List of representative scenarios to be analyzed has been prepared and discussed with the NRC staff.

• Baseline MELCOR calculations should be completed, pending the receipt of requested data from GE.

• Anticipate completion (MELCOR) within 2-3 months.

18


PREPRE--ACCIDENT INITIALIZATIONACCIDENT INITIALIZATION• Approach developed in collaboration with NRC.• Set full power (4500 MW) and the design feedwater flow

rate (2451 kg/s) for the duration of simulation.• Approach to steady-state was relatively smooth• Iterated with specified loss coefficients to arrive at

pressure drop and flow rates (feedwater, recirculation and steam) listed in the DCD:• Additional work is needed to resolve the apparent differences with

DCD conditions• Clarification on the physical locations of the referenced pressure

differentials needed from GE• Need detailed information on the various form loss coefficients

from lower plenum to the chimney region (along the core), the leakage flow paths from the chimney and separators to the downcomer.

19


PRELIMINARY RESULTS (PREPRELIMINARY RESULTS (PRE--ACCIDENT ACCIDENT INITIALIZATION)INITIALIZATION)

0

2000

4000

6000

8000

10000

12000

14000

16000

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0

time [sec]

Mas

s Fl

ow R

ate

[kg/

s]

Total flow rate through the core (CFVALU.910)Feedwater flow rate (CFVALU.127)Flow rate from outside the separators to DC (FL-MFLOW.191)Total flow rate through the main steam lines

20


RPV PressureRPV Pressure

7

7.05

7.1

7.15

7.2

7.25

7.3

7.35

7.4

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0

time [sec]

Pres

sure

[MPa

]

Steam dome (CVH-P.190)Separators (CVH-P.180)Chimney (CVH-P.139)Core region (CVH-P.134)Core region (CVH-P.131)Lower plenum (CVH-P.120)Downcomer (CVH-P.110)

21


Pressure Drop Between Various Core Pressure Drop Between Various Core Control VolumesControl Volumes

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

8.0E+04

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0

time [sec]

Pres

sure

dro

p (P

a)

CV120-CV131CV131-CV132CV132-CV133CV133-CV134CV134-CV139CV134-CV120

22


Fuel TemperatureFuel Temperature

0

200

400

600

800

1000

1200

1400

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0

time [sec]

Tem

pera

ture

[K]

COR-TFU.103COR-TFU.104COR-TFU.105COR-TFU.106COR-TFU.107COR-TFU.108COR-TFU.109COR-TFU.110COR-TFU.111COR-TFU.112COR-TFU.203COR-TFU.204COR-TFU.205COR-TFU.206COR-TFU.207COR-TFU.208COR-TFU.209COR-TFU.210COR-TFU.211COR-TFU.212

23


MELCOR SteadyMELCOR Steady--State Results vs. GE DCD State Results vs. GE DCD ValuesValues

Parameters Design value Simulated value Steam flow rate (kg/s) 2433 2437 Feedwater flow rate (kg/s) 2451 2439 Core coolant flow rate (kg/s) 9034-10584 9454 System pressure, nominal in steam dome (kPa) 7171 7179 System pressure, nominal core design (kPa) 7240 7243 Core inlet temperature (°C) 543-545 543 Total core pressure drop (from bottom of the core support plate to top of the core) (kPa) 70.0 47.0

Core plate pressure drop (kPa) 41.3 31.5 Core maximum exit void fraction 0.916 0.90 Downcomer liquid level (m) 17.27 17.6

24


MELCORMELCOR--Simulated Accident ScenarioSimulated Accident ScenarioTransient event initiated by a loss of feedwater (i.e., scenario T_DP_nIN of the ESBWR PRA):

Short or long-term coolant injection to RPV not available (i.e., GDCS injection to RPV & wetwell injection through equalization lines not available).ADS is assumed to be actuated if downcomer water level drops below 11 m.Heat removal by ICs not credited.PCC & PCC/IC pool makeup available (thereby allowing long-term containment heat removal).GDCS deluge system is also available for injection onto the lower drywell floor.

25


MELCORMELCOR--Simulated Accident Scenario Simulated Accident Scenario (Cont.)

Two cases considered:Case 1: MCCI allowed to occur (assuming MELCOR standard basaltic concrete composition).Case 2: MCCI suppressed

26


Preliminary Results Preliminary Results (Case 1: With MCCI)(Case 1: With MCCI)

Event Value

RPV depressurization starts (DPVs open), hour 0.33

Start of core uncovery, hour 0.86

Start time of gap release from fuel, hour 1.08 Range of relocation periods in various core regions (i.e., fuel temperature exceeds 2500 K), hour 1.69 – 3.82

Local failure of the lower core plate (i.e., T=1273K), hour 2.26 – 2.52

Gross failure (melting) of the lower core plate (i.e., T> 1700K), hour N/A

RPV lower head penetration failure, hour 3.91

Start of MCCI, hour 4.20

27


Preliminary Results Preliminary Results (Case 1: With MCCI) (Cont.)(Case 1: With MCCI) (Cont.)

Event Value

Water in reactor cavity reaches saturation, hour 4.36

Actuation of the cavity deluge system, hour 7.26

Time of GDCS water depletion, hour 9.0

Total in-vessel hydrogen generation, kg 603 Percentage of total core zirconium oxidized prior to vessel breach, % 18.0

Pressure in upper drywell at 24 hours, bar-abs 12.5

Maximum atmosphere temperature in upper drywell, K 801 Water level in drywell at 24 hours (relative to bottom of the RPV), m 11.5

Total combustible gas generation due to MCCI at 24 hours, kg 4426 kg of CO3038 kg of H2

Axial concrete erosion at 24 hours, m 1.42

28


RPV Pressure (Case 1: With MCCI)RPV Pressure (Case 1: With MCCI)Pressure in the RPV

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25

time [hr]

Pres

sure

[MPa

]

RPV pressure (CVH-P.190)

29


RPV Water Level (Case 1: RPV Water Level (Case 1: with MCCI)with MCCI)

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25

time [hr]

Wat

er L

evel

[m]

Water level in the vessel

30


Fuel TemperatureFuel Temperature

(Case 1: with MCCI)(Case 1: with MCCI)

0

500

1000

1500

2000

2500

3000

0 2 4 6 8 10

time [hr]

Tem

pera

ture

[K]

COR-TFU.104COR-TFU.112COR-TFU.204COR-TFU.212COR-TFU.304COR-TFU.312COR-TFU.404COR-TFU.412COR-TFU.504COR-TFU.512

31


Temperature of Debris on the Core Temperature of Debris on the Core PlatePlate (Case 1: with MCCI)(Case 1: with MCCI)

0

500

1000

1500

2000

2500

3000

0 2 4 6 8 10 12 14

time [hr]

Tem

pera

ture

[K]

COR-TPD.103COR-TPD.203COR-TPD.303COR-TPD.403COR-TPD.503

32


Debris Temperature in the Lower Debris Temperature in the Lower PlenumPlenum (Case 1: with MCCI)(Case 1: with MCCI)

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12 14

time [hr]

Tem

pera

ture

[K]

COR-TPD.101COR-TPD.201COR-TPD.301COR-TPD.401COR-TPD.501

33


Total InTotal In--Vessel Hydrogen Vessel Hydrogen GenerationGeneration (Case 1: with MCCI)(Case 1: with MCCI)

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25

time [hr]

Mas

s [k

g]

COR-DMH2-TOT

34


Total Gas Generation Due to CoreTotal Gas Generation Due to Core--Concrete Interaction (Case 1: with MCCI)Concrete Interaction (Case 1: with MCCI)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 5 10 15 20 25

time [hr]

Mas

s [k

g]

CAV-MEX.CO.1CAV-MEX.CO2.1CAV-MEX.H2.1CAV-MEX.H2O.1

35


Upper Drywell and Wetwell Pressure Upper Drywell and Wetwell Pressure (Case 1: with MCCI)(Case 1: with MCCI)

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

0 5 10 15 20 25

time [hr]

Pre

ssur

e [P

a]

CVH-P.410CVH-P.515Containmnet rupture pressure

36


Containment Concrete Floor Containment Concrete Floor Temperature Temperature (Case 1: with MCCI)(Case 1: with MCCI)

300

350

400

450

500

550

0 5 10 15 20 25

time [hr]

Tem

pera

ture

[K]

HS-TEMP.4000105Deluge system activation setpoint

37


Debris Pool Temperature in the Lower Debris Pool Temperature in the Lower Drywell (Case 1: with MCCI)Drywell (Case 1: with MCCI)

0

500

1000

1500

2000

2500

0 5 10 15 20 25

time [hr]

Tem

pera

ture

[K]

CAV-T.HMX.1Basaltic Concrete Decomposition Temperature

38


Water Level on the Containment Water Level on the Containment Floor (Drywell)Floor (Drywell) (Case 1: with MCCI)(Case 1: with MCCI)

-10

-5

0

5

10

15

0 5 10 15 20 25

time [hr]

Wat

er L

evel

[m]

Water level in the drywellBottom of drywell

39


MELCOR 1.8.5 CPU TimeMELCOR 1.8.5 CPU Time

(Case 1: with MCCI)(Case 1: with MCCI)

0

5

10

15

20

25

30

0 5 10 15 20 25

time [hr]

CPU

Tim

e (h

r)

CPU Time

40


Sensitivity to MELCOR Lower Head Sensitivity to MELCOR Lower Head Model ParametersModel Parameters

Cases

HTC (debris-

LH) (W/m2K)

Debris

quenching HTC

(W/m2K)

Debris dryout HTC

(W/m2K)

Debris fall velocity

(m/s)

Particulate debris size

(m)

Porosity of

particulate debris

Conduction enhancement

for molten components

Radiation exchange

factor

Candling HTC

(W/m2K)

Case 1 1000 (def.) 100 (def.) ~11 (def.

C1242) 1.0 (def) 0.001 0.3 3200K/0.01 (def) 0.25 (def) 1000 (def)

Case 2 100

Case 3 10000

Case 4 0.5

Case 5 20(2) 220 0.025 0.4 FCELR and FCELA=0.1 others=0.25

7500 for UO2, Zr,

ZrO2 others=2500

Case 6 Best Estimate

200 1300 0.025 0.5 FCELR and FCELA=0.1 others=0.25

7500 for UO2, Zr,

ZrO2 others=2500

41


Sensitivity to MELCOR Lower Head Sensitivity to MELCOR Lower Head Model Parameters (Cont.)Model Parameters (Cont.)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 (Bestestimate)

Scenario

Tim

e (h

r)

Start time of MCCITime of RPV lower head penetration failureStart time when melt mass relocates to the lower plenum

42


Comparison With MAAP Results (Case 2: Comparison With MAAP Results (Case 2: Without MCCI)Without MCCI)

Event MAAP* MELCOR

RPV depressurization starts (DPVs open), hour 8.6×10-3 0.33

Start of core uncovery, hour 0.36 0.86 Onset of core damage (i.e., fuel temperature exceeds 2500 K), hour 0.97 1.69

RPV lower head penetration failure, hour 6.3 3.91

Deluge system actuated, hour 6.3 7.9

Containment (upper drywell) pressure at 24 hours, bar-abs 5.0 4.8

Containment (lower drywell) temperature at 24 hours, K 425 427

Containment fail/vent, hour N/A N/A

PCCS heat removal at 24 hours, MW 18.5 22.7 Water level in drywell at 24 hours (relative to bottom of the RPV), m 13.1 12.5

Axial concrete erosion in 24 hours, m 0.07 0.0

Mass fraction of noble gases released to environment 9.0×10-4 8.7×10-4

Mass fraction of CsI released to environment 7.4×10-5 1.8×10-5

*MAAP results taken from NEDC-33201P (Rev 0)

43


RPV Pressure (Case 2: Without MCCI)RPV Pressure (Case 2: Without MCCI)

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25

time [hr]

Pres

sure

[MPa

]

CVH-P.190MAAP Results

MAAP results taken from NEDC-33201P (Rev 0)

44


Upper Drywell and Wetwell PressureUpper Drywell and Wetwell Pressure

(Case 2: Without MCCI)(Case 2: Without MCCI)

0.0E+00

1.0E+05

2.0E+05

3.0E+05

4.0E+05

5.0E+05

6.0E+05

0 5 10 15 20 25

time [hr]

Pres

sure

[Pa]

CVH-P.410CVH-P.515MAAP Results


45


Lower Drywell TemperatureLower Drywell Temperature


0

100

200

300

400

500

600

0 5 10 15 20 25

time [hr]

Tem

pera

ture

[K]

CVH-TVAP.405MAAP results


46


Decay Heat Generation and Heat Removal by Decay Heat Generation and Heat Removal by PCCS (Case 2: Without MCCI)PCCS (Case 2: Without MCCI)

0

50

100

150

200

250

300

350

0 5 10 15 20 25

time [hr]

Pow

er [M

W]

Decay heatHeat removal by PCCSMAAP results


47


Water Level in the Drywell Water Level in the Drywell


-10

-5

0

5

10

15

0 5 10 15 20 25

time [hr]

Wat

er le

vel [

m]

Water level in drywellMAAP results


48


Release of Noble Gases to the EnvironmentRelease of Noble Gases to the Environment


1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25

time [hr]

Xe

rele

ase

frac

tion

[-]

MELCOR results (RN1-TYCLT-1-2.9)MAAP results


49


Release of CsI to the Environment Release of CsI to the Environment

(Without MCCI)(Without MCCI)

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25

time [hr]

CsI

rele

ase

frac

tion

[-]

MELCOR results (RN1-TYCLT-16-2.9)MAAP results

MELCOR calculations use the CORSOR-BOOTH option for in-vessel releasesMAAP results taken from NEDC-33201P (Rev 0)

50


SUMMARYSUMMARY

Generally, MELCOR and MAAP results are in reasonable agreementDesirable to have a discussion of MAAP modeling/parametric assumptions to better resolve some of the observed differences, e.g.,

Debris/water/LH interactions

Comparison of calculated source term

51


• Containment spray system• The elevation of the containment spray header inside

the drywell;• Spray water temperature; and• Spray mean droplet diameter.

• Containment venting system• Elevations of containment venting system in both the

suction and the discharge sides; and• Length of various pipe sections in the vent lines.

REMAINING DATA NEEDSREMAINING DATA NEEDS

52


REMAINING DATA NEEDS (Cont.)REMAINING DATA NEEDS (Cont.)

• PCCS and IC system• The pipe wall thickness of the PCCS and IC inlet lines.• The inlet pipe location relative to PCCS/IC pool and if it is

insulated

• Additional BiMAC system design data may become necessary, after the DCD information is more carefully examined.

53


Planned CalculationsRationale for selection of scenarios:o To provide initial & boundary conditions for NRC

confirmatory analyses (e.g., FCI, DCH, BiMAC, etc.)o To enable limited comparison to MAAP predictionso To assess sensitivity to design/operational aspects (e.g.,

sprays)o To support other NRC objectives

“Frequency-dominant”, “risk-dominant” and “consequence-dominant” scenarios will be examined, together with influence of various assumptions and sensitivity cases

54


Case MELCOR SCENARIO

ACC. CLASS

COMMENTS

EXPLORATORY OR

CONFIRMATORY SENSITIVITIES

1 T_DP_nIN I High CDF,

Representative of low pressure sequences

Confirm BiMAC availability, PCCS damage/failure after core

damage

2a T_IRV_DP_nIN_nD I

Highest societal risk &

3rd highest societal consequences &

individual risk

Confirm Concrete types, overlaying water pool

2b T_IRV_DP_nIN_nDv I

3rd highest individual risk Confirm

2c T_IRV_DP_nIN_nD_M I

2nd highest risk & consequences &

individual risk Confirm

2d T_IRV_DP_nIN_nD_1in I

3rd highest societal

consequences Confirm

3a T_DP_nIN_W 2 II

Containment failure prior to CD, CHR fails @ 24

hrs Confirm

4 T_IC24_nD III

Representative of high-

pressure scenarios. Add DCH, HPME/creep rupture of MSL nozzles

and/or SRV

Explore Drywell spray activation impact on LDL water level

5

n/a (similar to #3, 15 cm GDCS

equalization line break)

II

Frequency-dominant

low-pressure sequence. Highest CDF LOCA

with initially intact containment

Explore

6a T_AT_DP_2x IV

3rd high societal risk Confirm

7a BOC_SD_nECC V

Highest societal consequences

Confirm

nrc-ge meeting 03-08-06-confirmatory melcor analysis of … · 2012. 11. 21. · fl812 fl813 fl814...

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