simulations of large break loca without safety … 2015, marseille march 24 – 26, 2015 simulations...

ERMSAR 2015, Marseille March 24 – 26, 2015

Simulations of large break LOCA without safety injection

for EPR reactor using MELCOR computer code

Piotr Darnowski, Eleonora Skrzypek, Piotr Mazgaj,

Michał Gatkowski

Warsaw University of Technology,

Institute of Heat Engineering, Poland

Session IV: SA Scenarios


Outline

1. Introduction

2. MELCOR model

3. Scenario and assumptions

4. Results

5. Conclusions

2


Introduction

Activities in the framework of the two projects: SARWUT (2013-2014)

and INSPE (2014-2015).

Initiation of the Severe Accident research – no activities in the field

before.

MELCOR 2.1 code. Models development: EPR, Zion PWRs and

BWR.

LBLOCA, SBO, Total Loss of AC Power and variations.

Cooperation with National Atomic Energy Agency (PAA), Areva NP,

GE-Hitachi NE and National Centre for Nuclear Research (NCBJ)

EPR selected because it is potential PWR design for the first polish

NPP (~ 3000 MWe, >2028).

3


MELCOR model

Model based on publicly available data, Ref. [1],[2].

Relatively simple nodalization (59 CVH, 74 FL, 117 HS).

Containment with single CV.

Model parameters, coefficient and setup based on SOARCA

recomendations Ref. [5].

4

LP

DC

UP

BYPASS

UH

Ring: 1 2 3 4 5 6

19181716151413121110987654321

Level:

CORE

Loop x3 Loop x1


MELCOR model

5

LP

DC

UP

BYPASS

UH

CORE

RPV and core model:

10 control volumes

19 axial levels and 6 rings

30 heat strucutres

EOC core


MELCOR model

6

CV

H 1

20

CV

H 1

40

CVH 130

FL 1

20

FL 1

10

FL 1

30

FL 507FL 5

02

FL 1

40

CVH 150

CVH 110

CV

21

0/2

40

CV

20

0/2

30

CV 220/250

FL 2

21

/24

2

FL 197/182

FL 2

21

/25

1

FL 198/181

FL 2

11

/24

1

FL 201/230

SG Secondary Side SG Primary Side

CV, FP & HS


MELCOR model

7

501502

510

50

8

511512

509

511

507 503

512 510

509 508

500501

502507

558

71

0

560

71

3

PDS

PSV

PRT Tank

1 Loop

HS4

06

00

559

71

2

Rupture disk

HS4

05

8

HS4055971

1

561

550

551

71

47

15

Containment

PRZ with single RCS loop and 1CV containment


Scenario

LBLOCA with complete loss of active safety injection - SA

for PWR type reactor.

Fast progressing sequence with core meltdown.

Comparison of two LB-LOCAs: 2A-LOCA (cold leg double

ended break) and SL-LOCA (surge line double ended

break).

Due to the Break Preclusion Principle 2A-LOCA is not a

design basis accident for the EPR reactor (Ref. [4],[6]).

Main motivation: to investigate differences between

2A-LOCA and SL-LOCA.

Only In-Vessel phase considered.

8


Assumptions

2A-LOCA (Cold-Leg) and SL-LOCA (Surge-Line).

Active safety injections (MHSI & LHSI) are not available.

Accumulators are available.

SCRAM at time zero, pumps cost-down starts at time zero.

MFW isolated at accident initiation.

MSIV closure at accident initiation.

EFWS available.

Secondary Partial Cooldown activated at SI signal (MSRV setpoint 95.5 bars to 60 bars in 20 min).

Pressurizer Discharge System (PDS) activated at core exit gas T=650 °C.

9


Results

10

SL-LOCA reference MAAP4.0.4 results available in

Ref. [3].

Containment peak pressure: 3.5 and 4.3 bar for SL-

LOCA and 2A-LOCA respectively. Reference [3] – 3.5

bar.

For 2A-LOCA Cathare V2.5 predicts 4 bars in

Ref. [8] and PAREO9 4.3 bars Ref. [7].

2A-LOCA SL-LOCA SL-LOCA (Ref. 3)

0 0 0

Start of core uncovery (S) 0.2 57 60

SI signal 7.2 148.5 N/A

ACC injection 11 152 120

ACC depletion 37.5 228.5 180

Containment pressure peak 103 183 100

PDS valves open 497 1702 1500

Start of oxidation 591 1587 1560

Core fully uncovered (C) 919 1926 N/A

Start of core melting 1024 1968 1740

Massive core relocation 4764 5834 7380

Vessel failure 6070 6732 10680

TIME [s]KEY EVENT

Pipe rupture


Results

11


0 0 0


SI signal 7.2 148.5 N/A

ACC injection 11 152 120

ACC depletion 37.5 228.5 180







Vessel failure 6070 6732 10680

TIME [s]KEY EVENT

Pipe rupture


12

2A-LOCA

Cladding Temperatures

for Inner Core Ring #1

SL-LOCA

Ref. [3]: 490 kg


Results

13

Mass in lower plenum before core plate failure (10-15 tons) – after ~160

tons.

16 minutes difference in massive relocation time.

11 minutes difference in RPV time-to-rupture.

RPV failure: 22 min and 15 min after relocation for 2A-LOCA and SL-LOCA

respectively.

SL-LOCA RPV breach – 1h 05min before MAAP4 (Ref. [3]).


0 0 0



7.2 148.5 N/A

11 152 120

37.5 228.5 180






6070 6732 10680

TIME [s]

SI signal

ACC injection

ACC depletion

Vessel failure

KEY EVENT

Pipe rupture


0 0 0



7.2 148.5 N/A

11 152 120

37.5 228.5 180






6070 6732 10680

TIME [s]

SI signal

ACC injection

ACC depletion

Vessel failure

KEY EVENT

Pipe rupture


Issues

Heavy Reflector is modeled as HS in MELCOR.

In EPR sideward reflector melt-through is expected and relocation through downcomer.

MELCOR allows relocation through core bypass (TMI like) but not through the downcomer.

New model with HR being a part of COR package is considered.

14

TMI

LP

DC

UP

BYPASS

UH

CORE

EPR


Conclusions

Containment pressure peak 0.8 bar difference for 2A-LOCA and SL-LOCA.

Similar H2 production.

10-15 minutes difference in core degradation phenomena beetwen 2A-LOCA and

SL-LOCA - core relocation and RPV rupture.

Vessel failure earlier in comparison to Ref. [3] results by one hour for SL-LOCA.

Model needs further development.

Uncertainty and sensitivity is recommended.

15


Future plans

Sensitivity and Uncertainty studies.

Presented model is under development.

Detailed containment modifications in progress.

Detailed RPV model in progress.

Simulations of Ex-Vessel phase.

Other activities (ASTEC code, RELAP/SCADAP code,

experiments, ISPs, Fukushima, TMI, Re-criticality

during SA).

16


References

17

[1] Areva & EDF, 2013. The Pre-Construction Safety Report (PSCR) for UK EPR Reactor, www.epr-reactor.co.uk.

[2] U.S. EPR Application Documents, Final Safety Analysis Report, 2014

[3] UK EPR GDA Submission, The Pre-Construction Safety Report (PCSR), Chapter 16.2 RCC-B – Severe Accident Analysis

[4] Chapuliot, S., Migné, C., Break Preclusion Concept and its Application to the EPRTM Reactor, Nuclear Engineering and Design,

Volume 269, 97-102, 2014

[5] Sandia National Laboratories, MELCOR Best Practices as Applied in the State-of-the-Art Reactor Consequence Analyses

(SOARCA) Project, Nuclear Regulatory Commission, NUREG/CR-7008, 2014.

[6] UK EPR GDA Submission, The Pre-Construction Safety Report (PCSR), Chapter 5.2 – Integrity of the Reactor Coolant Pressure

Boundary

[7] UK EPR GDA Submission, The Pre-Construction Safety Report (PCSR), Chapter 16.4 – Specific Studies

[8] UK EPR Fundamental Safety Overview, Volume 2: Design and Safety, Chapter F: Containment Systems and Safeguard

Systems, Subchapter: F.2 Section F.2.1., 2014


Acknowledgments

The publication was financed and partially created in the framework of a

project: Innovative Nuclear and Sustainable Power Engineering (INSPE) on

The Faculty of Power and Aeronautical Engineering at Warsaw University

of Technology. The INSPE is co-financed with EU funds by European

Social Fund.

Presented model was partially created in the framework of a strategic

project NCBiR: “Technologies for the development of safe nuclear energy”,

Research Task No. 9 entitled “Development and implementation of safety

analysis methods in nuclear reactors during disturbances in heat removal

and severe accident conditions”

18


Thank you for your attention

Contact:

[email protected]

[email protected]


Additional Slides

20


Break Preclusion Principle

21

Ref. [2]

Ref. [2]


22


Results

23


Additional slides

24


Additional Slides

25

LP

DC

UP

BYPASS

UH

CORE

LP

DC

UP

BYPASS

UH

Ring: 1 2 3 4 5 6

19181716151413121110987654321

Level:

CORE


Containment

IRWST – 2086 m3 of water

Containment RH=0.5, p=1 bar, V=78500 m3

47 PARS – default MELCOR

ACCx1 m=29667kg ACCx3 m=89334 kg water mass

ACC setpoint 45 bars

SI signal + Partial Cooldown = 115 bar

RT, TT – 135 bar

26


Steady State

27

Time [s]: -0.97

Pressurizer Pressure [Pa]: 15501700.00

HLx1 Flow [kg/s]: 5571.76

CLx1 Flow [kg/s]: 5574.31

HLx3 Flow [kg/s]: 16793.30

CLx3 Flow [kg/s]: 16789.60

CL Total Flow [kg/s]: 22363.90

HL Total Flow [kg/s]: 22365.00

RCS Water Inv. [kg]: 271151.00

PRZ Level [m]: 6.73

PRZ Water Mass [kg]: 22537.00

Feedwater Flow x1 [kg/s]: 657.51

Feedwater Flow x3 [kg/s]: 1972.52

SGx1 Outflow [kg/s]: 657.50

SGx3 Outflow [kg/s]: 1972.40

SGx1 Pressure [Pa]: 7706760.00

SGx3 Pressure [Pa]: 7708300.00

SGx1 Level [m]: 14.93

SGx3 Level [m]: 14.93

SGx1 Water Mass [kg]: 77970.60

SGx3 Water Mass [kg]: 233847.00


MAAP4 – Ref. [3] Results

28


MAAP4 – Ref. [3] Results

29


Additional Slides

30


Additional Slides

31

From: EMUG 2010, New ‚Best Practice’ Default Values for MELCOR 2.1

Several tons of debris material was spotted in LP, before core plate

failure.

It is not unusual in MELCOR simulations.

EPR


Additional Slides

32

SL-LOCA Fuel Temperatures


Additional Slides

33


Additional Slides

Simulation setup

34

No. Field(s) Type/Package Unit(s) SOARCA DFT186 DFT21

1 HFRZUO UO2 7500 1000 7500

2 HFRZZR Zr 7500 1000 7500

3 HFRZSS Steel 2500 1000 2500

4 HFRZZX ZrOX 7500 1000 7500

5 HFRZSX SSOX 2500 1000 2500

6 HFRZCP Poison 2500 1000 2500

7 FCELR Radial 0.1 0.25 0.1

8 FCELA Axial 0.1 0.25 0.1

9 4413(5) S.C. 1.00E-06 0.05

10 4414(1) S.C. 0.01 0.001 0.01

11 4415(1) S.C. 1 0.5 1

12 4055(2) S.C. 0.5 5.00E-04 0.5

13 1001(1,2) S.C. Zr - O2 reaction - low temp. range const coeff kg2/m4/s 26.7 50.4 26.7

14 1001(2,2) S.C. Zr - O2 reaction - low temp. range exp. constant K 17490 14630 17490

15 1001(3,2) S.C. Zr - O2 reaction - high temp. constant coeff kg2/m4/s 26.7 0 26.7

16 1001(4,2) S.C. Zr - O2 reaction - high temp. exp. constant 17490 0 17490

17 1001(5,2) S.C. Zr - O2 reaction - upper temp. Bound. For low range 9998 10000 9998

18 1001(6,2) S.C. Zr - O2 reaction - upper temp. Bound. For high range 9999 10000 9999

19 1004(1) S.C. Oxidation cutoff temperatures - minimum 1100 1100 1100

20 1250(1) S.C. COR package temp. For enhanced debris-LH conduction 2800 3200 2800

21 1505(1) S.C. - 0.05 0.001 0.05

22 1505(2) S.C. - 0.05 0.001 0.05

23 1600(1) S.C. - 1 0 1

24 1603(2) S.C. COR package min yield stress temperature K 1700 1800 1700

25 IACTV BUR -

26 KFLSH FL -

27 DRGAP COR m

28 HDBPN COR HTC from debris to penetration structures W/m2/K 100 1000 1000

29 HDBLH COR W/m2/K 100 1000 1000

30 MDHMPO COR - MODEL 1000 1000

31 MDHMPM COR - MODEL 1000 1000

32 TPFAIL COR Failure temp.of the penetrations or the LH K 9999 1273.15 1273.15

33 CDISPN COR Discharge coef. for debris through failed penetration - 1 1 1

34 HDBH2O COR W/m2/K 2000 100 100

35 VFALL COR m/s 0.01 1 1

36 IAICON COR - Not active Not active Not active

37 PORDP COR Porosity of particulate debris defaults N/A - 0.4 0.4 0.4

38 DHYPD COR Debris equivalent diamter Core/LP defaults N/A m 0.01/0.002 0.01/0.002 0.01/0.002

39 1132(1) S.C. K 2800 3100 3100

40 1141(2) S.C. kg/m/s 0.2 1 1

41 4401(3) S.C. Max numb. Of iter. Permitted before solution is repeated - 15 default default

42 CPFPL/CPFAL HS -

43 EMISWL HS - 0.27 Not active Not active

44 RMODL HS - EQ-BAND Not active Not active

45 PATHL HS m 0.1 Not active Not active

46 DEGAS HS DEGAS model - not active due to numerical problems -

47 MLT MP Material interactions parameters - nuemrical problems -

48 IRODDOMAGE COR - SOARCA Not active Not active

49 RCLADTHICKNESS COR Min. Unox. clad thick. under which Fuel Failure Table works m 5.70E-05 Not active Not active

50 DRZRMN COR m 1.00E-04 1.00E-04 1.00E-04

51 DRSSMN COR m 1.00E-04 1.00E-04 1.00E-04

COR package min. porosity for flow and HT

COR package 1-dim stress/strain distribution

HS temperature convergence criterion

CVH/FL direct versus iterative solution algorithm

COR package min. CVH volume fraction

COR_CHT W/m2/KCandling Heat transfer coefficient

Radiation heat transfer coefficientCOR_RF

Description

Not active

Not used

0.0/1.0 core; 0.5/0.5 elsewhere

BUR package was not active

Not active

Higher than 0

K

-

Burn package activation

Superheated pool flashing model

Thickness of gas gap

Flow blockage friction parameters

HTC from debris to LH

HTC from oxidic pool to lower head

HTC in-vessel failing debris to pool

Velocity of failing debris

Control rods release model

HTC from metalic pool to lower head

Nominal optical distatnce

Fuel Failure Table

Critical min. thickness of unox steel

Fuel rod collapse temeprature

Max. Molten Zr breakout flow rate

Pool fraction HS settings

Steel emissivity

Eq. Band radiation

Critical min. thickness of unox zircaloy


Additional Slides

35


Additional Slides

36


Additional Slides

37