ImpactsofCladdingBurstCriteriaonLOCASafetyAnalysis

September10,2017RamadaPlazaJeju,Korea

JoosukLeejslee2@kins.re.kr

Contents1. IntroducAon2. Analysisdetails

• appliedburstcriteria,modelingdetailsetc.

3. AssessedproperAes• Claddingtemperatures• ECR

4. Summary

‣ For the period of large break loss-of-coolant accident(LBLOCA), fuel rod can be ruptured due to the excessive plastic deformation of zirconium alloy cladding at high temperature(ballooning and burst).

‣ Cladding ballooning can reduce the sub-channel flow area. Heat conduction from fuel pellet to coolant is also strongly affected by the gap width, which can be varied with the extent of ballooning. Thereby prediction of cladding ballooning and burst is important.

‣ Typically, two types of cladding burst criteria at high temperature are established, a strain-based or a stress-based.

‣ In this work, effects of fuel rod burst criteria on the PCT and ECR for the LOCA period were assessed.

1. Introduction

✤ Appliedburstcriteria

2. Analysis Details

1000 1100 1200 1300 1400 1500

0

50

100

150

200

250

300

350

True

hoo

p st

ress

at b

urst

, MPa

Rupture temperature, K

+100 MPa

-40 MPa

900 1000 1100 1200 1300 1400 1500 1600

0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

+100%

Burs

t stra

in

Rupture temperature, K

-80%

NUREG-0630fast ramp

Stressbasedcriterion:-adaptedinFRAPTRAN

Strainbasedcriterion:-NUREG-0630

>10MPa

+40 MPa

2. Analysis Details✤ AnalysiscondiAons

‣ Initiation of LOCA was supposed to occur at the fuel burnup of 30MWd/kgU. PLHR before LOCA was set to 14.5 kW/ft. PLUS7 fuel with ZIRLO cladding was utilized, and 20 evenly spaced axial nodes were allocated at the fuel rod.

‣ Thermal-hydraulic boundary conditions, such as coolant heat transfer coefficient(HTC), coolant pressure and temperature during LOCA period were obtained from APR1400 LBLOCA analysis.

‣ LOCA analysis was performed by using the MARS-KS1.3, which is a regulatory auditing system code in Korea.

✤ AnalysiscondiAons

‣ Fuel rod ballooning and burst phenomena strongly depend on the rod internal pressure(RIP), heat transfer coefficient(HTC) of coolant, and fuel thermal conductivity(FTC).

• Thereby, uncertainties of RIP, HTC and FTC were also considered, and these were assumed as ±2σ, ±50%, and ±2σ, respectively.

‣ For the combined uncertainty analysis, 124 code runs based on simple random sampling were carried out.

‣ FRAPCON-4.0/FRAPTRAN-2.0 fuel performance code was used in this calculation.

• (pseudo)claddingtemperaturesinAPR1400LBLOCA;basecase

3. Assessed properties

1082K996.1K

100 120 140 160 180 200

200

400

600

800

1000

1200

1400

1 1 1 1

11

3 42

107

1

Cla

ddin

g te

mpe

ratu

re, K

Time, s

stress criterion base case

0 20 40 60 80 100 0

10

20

30

# of

faile

d ro

d

100 120 140 160 180 200

200

400

600

800

1000

1200

1400

13 2

7

2 3 2

15

5

1

0 20 40 60 80 100

Cla

ddin

g te

mpe

ratu

re, K

Time, s

strain criterion base case

0

10

20

30

# of

faile

d ro

d

Stressbasedcriterion:(withHTC,FTC,RIPuncertainty,butw/oburstcriteriauncertainty)

Strainbasedcriterion:(withHTC,FTC,RIPuncertainty,butw/oburstcriteriauncertainty)

124 SRS cladding temperatures

PCT distribution

900 1000 1100 1200 13000

4

8

12

16

20Burst criteria

strain stress

The 3rd highest PCTstress: 1288.6Kstrain: 1290.9K

Freq

uenc

y co

unt

Peak cladding temperature, K

0

20

40

60

80

100

120

Cum

ulat

ive

Cou

nt

900 1000 1100 1200 1300 1400 15000

4

8

12

16

20Burst criteria

strain stress

Freq

uenc

y co

unt

Peak cladding temperature, K

0

20

40

60

80

100

120

Cum

ulat

ive

Cou

ntThe 3rd highest PCTstress: 1238.8Kstrain: 1261.4K

BlowdownPCT: RefloodPCT:

ECR distribution

2 3 4 5 60

10

20

30

40

50

60

70

80

Burst criteria strain stress

Freq

uenc

y co

unt

ECR, %

0

20

40

60

80

100

120

Cum

ulat

ive

Cou

nt

The 3rd highest ECRstress: 4.38%strain: 4.34%

‣ BurstcriteriauncertaintydoesnotinduceanymeaningfuleffectsonthePCTandECRchanges.

‣ ThisisduetotheinherentnatureofFRAPTRANballooningmodelandcurrentfixedthermal-hydraulicboundarycondiAons.

‣ OncetheballooningmodelisacAvated,nofurtherstrainiscalculatedforanyaxialnodes.

100 120 140 160 180 200

200

400

600

800

1000

1200

1400

1 1 1 1

11

3 42

107

1

Cla

ddin

g te

mpe

ratu

re, K

Time, s

stress criteria base case

0 20 40 60 80 100 0

10

20

30

# of

faile

d ro

d

100 120 140 160 180 200

200

400

600

800

1000

1200

1400

13 2

7

2 3 2

15

5

1

0 20 40 60 80 100

Cla

ddin

g te

mpe

ratu

re, K

Time, s

strain criteria base case

0

10

20

30

# of

faile

d ro

d

900 1000 1100 1200 13000

4

8

12

16

20Burst criteria

strain stress

The 3rd highest PCTstress: 1288.6Kstrain: 1290.9K

Freq

uenc

y co

unt

Peak cladding temperature, K

0

20

40

60

80

100

120

Cum

ulat

ive

Cou

nt

900 1000 1100 1200 1300 1400 15000

4

8

12

16

20Burst criteria

strain stress

Freq

uenc

y co

unt

Peak cladding temperature, K

0

20

40

60

80

100

120

Cum

ulat

ive

Cou

ntThe 3rd highest PCTstress: 1238.8Kstrain: 1269.1K

Burst criteria uncertainty effects

‣ EffectsofcladdingburstcriteriatothefuelrodperformanceforaLOCAperiodwereassessed.Stress-based(adaptedinFRAPTRAN-2.0)andstrain-based(NUREG-0630fastramp)burstcriteriawereusedinthisanalysis.FollowingsareidenAfied.

• BurstcriteriaalmostdidnotchangetheblowdownPCTandECR.

• ButsmalldifferencesonrefloodPCTwerediscovered.

• BurstcriteriauncertaintyalsodidnotinduceanymeaningfuleffectsonthePCTandECR.

‣ AboveresultsarevalidwithincurrentanalysiscondiAons(ex,fixedthermalBC).Butiftheheattransfercoefficientswereinfluencedbytheextentofcladdingballooning,aboveconclusionsmightbechanged.

Summary

Safety together, Better tomorrow