NSRR High Burnup Fuel Tests for RIAs and BWR Power Oscillations without Scram

T. Nakamura, H. Sasajima, J. Nakamura and H. UetsukaFuel Safety Research Lab. JAERI, Japan

Prepared for NSRC 2002 Oct. 29, 2002 at Washington D.C., USA

JAERI 1

Objectives of the NSRR TestsClarify influence of fuel burnups on- Fuel failure threshold and its mechanism- Consequence of the failure

(Fission gas release, fuel fragmentation & dispersal, etc. )under Reactivity-initiated accident (RIA), and toExamine fuel behavior under cyclic power transient conditions

simulating BWR power oscillations without scram

Fuel fragmentation& dispersal

Steam generation

Cross section

Cracking

Fission gas bubbles

High burnup (rim) structure

Oxide

Hydrides

Cladding deformationdue to PCMI

Thermal and fission gasbubble expansion of the pellets

Fission gas release

JAERI 2

Mechanism to cause failure Consequences of failure

NSRR (Nuclear Safety Research Reactor)

Inlet of offset loading tube

Reactor pool

Offset loading tube

Control rod driving mechanisms

Vertical loading tube

Driver coreExperimentalcapsule

6 Regulating rods2 Safety rods

3 Transient rods149 Driver core fuels

Test fuel

Experimental capsule

Experimental cavity

272J/g(65cal/g)

0.23 0.24 0.25 0.26 0.27

542J/g(130cal/g)

0

50

100

150

Time (s)

Line

ar h

eat

rate

(M

W/m

)

JAERI 3

200 mm

1250

mm

OuterCapsule

Test FuelRod

InnerCapsule

Test Capsule Instrumentation

Test Fuel Rod

Rod InternalPressure Sensor

Cladding SurfaceTemperature

Water Temperature

ElongationSensors

Water ColumnVelocity Sensor

Irradiation Capsule and Instrumentation

Strain gage

JAERI 4

NSRR Test Fuel & Burnups

Fuel type

Highly enrichedUO2 Irradiated

in JMTR

PWR

ATR/MOX

BWR

Pellet Burnup (GWd/t)

10 20 30 40 50 60Number of tests

Remarks

16failure >62cal/g

at 61GWd/t

22, failure >667J/g(160cal/g) at 38GWd/t

24 failure >60cal/g

at 50GWd/t

5no failure <140cal/g

at 20GWd/t

Test plan in 2002-2006

UO2 EU [<74GWd/t] JP [60GWd/t]

MOX ALPS[59GWd/t]

MOX [30-45GWd/t]

70 80

MOX

MOX

UO2

UO2

MOX

UO2 EU [<75GWd/t] JP [61-65GWd/t]

MOX EU[<78GWd/t]

Tests to be conducted in 2002-2003

UO2

JAERI 5

Power oscillation [25GWd/t]

EU: European fuel, JP: Japanese fuel

Brittle

Ductile

Oxide Hydride clusters

Key Observations in NSRR/RIA Tests(1) Hydride-assisted PCMI failure at low enthalpies (2) Consequence of fuel failure

(i) Fission gas release(ii) Fuel fragmentation

PWR50GWd/t

(hydrogen: about 400ppm) failed at 250J/g(60cal/g) BWR

61GWd/t(Hydrogen: about 200ppm)

failed at 292J/g(70cal/g)

Brittle

Ductile Zr liner

RIA Test ResultsJAERI 6

Test FK-90

90

Top Bottom20 mm

Fue

l rod

pow

er (M

W/m

)

Cla

ddin

g te

mpe

ratu

re (?

C)

[Cal

cula

ted

with

FR

AP

-T6]

Rod

inte

rnal

pre

ssur

e (M

Pa)

0.25 0.26 0.27 0.280

50

100

150

200

0

5

10

15

20Test FK-9 Time of failure

at 359J/g(86cal/g)

Rod power ( x 2 MW/m)

Average

Surface

Time (s)

BWR fuel at 61GWd/tU

(1) Hydride-assisted PCMI failure at low enthalpiesJAERI 7

PCMI Failure Thresholds

HBO-1 50GWd/t 250J/g(60cal/g)HBO-5 44GWd/t 321J/g(77cal/g)TK-2 48GWd/t 250J/g(60cal/g)TK-7 50GWd/t 359J/g(86cal/g)

FK-6 61GWd/t 292J/g(70cal/g)FK-7 61GWd/t 259J/g(62cal/g)FK-9 61GWd/t 359J/g(86cal/g)FK-10 61GWd/t 334J/g(80cal/g)

0 10 20 30 40 50 60 700

50

100

150

200

250

Pellet Average Fuel Burnup (GWd/tU)

Ent

halp

y In

crea

se (

cal/g

)

PCMI failure threshold(by the Japanese Nuclear Safety Commission)

No failure Failure Test ID No failure Failure

NSRR

Test ID

PWR

BWR

SPERT, PBF

CABRI UO2

CABRI MOX

JMTR

ATR/MOX

0

200

400

600

800

1000

Ent

halp

y In

crea

se (

J/g)

PWR fuel burnupsand failure enthalpies

JAERI 8

BWR fuel burnupsand failure enthalpies

Failure Map in Terms of Hydrogen Content and Fuel Enthalpy for BWR Fuel

0

250

500

750

0 50 100 150 200 250

Hydrogen content (wtppm)

Fue

l ent

halp

y (J

/g)

FailureNo Failure

solid: failedopen: not failed

Fuel failure correlates well to hydrogen content in cladding in BWR fuel tests.

JAERI 9

Fresh PWR Fuel Tests with Hydrided Cladding

Brittle cladding fracture due to PCMI occurred in fresh PWR fuel tests with hydridedcladding, similar to high burnup fuel tests.

JAERI 10

0.0

1.0

2.0

3.0

0 500 1000

Hydrogen content (%)

Cla

dd

ing

ho

op

str

ain

(%

)[c

alc

ura

ted

pe

ak]

Fresh PWRfailureno failure

5 cm

0.3 mm

Fuel stack

1 cm

Cross section of crack

Longitudinal crack of about 10cm generated over the fuel stack

0.0

1.0

2.0

3.0

0 500 1000

Hydrogen content (%)

Cla

dd

ing

ho

op

str

ain

(%

)[c

alc

ura

ted

pe

ak] Fresh PWRfailureno failure

Failure Criteria of Hydrided CladdingEstimated peak strains to cause the failure was larger in fresh fuel tests, suggesting influence of the irradiation embrittlement of the cladding.

Failure threshold differs depending on cladding type, suggesting hydride precipitation morphology effects.

Irradiated PWR rod failure

Fresh PWR rod failureIrradiated

BWR rod failure

JAERI 11

Transient hoop deformation of irradiated fuel cladding by PCMI during early phase of RIA transient was measured for the first time.

The hoop deformation was about 0.4% at fuel enthalpy of about 80cal/g.

Transient Hoop Strain MeasurementJAERI 12

0.24 0.25 0.26 0.27 0.28 0.29

StrainReactor power

Time of failureat 334J/g (80cal/g)

0

0.1

0.2

0.3

0.4

0.23 0.25 0.27Time (s)

Cla

ddin

g ho

op s

train

(%

)

Strain

Reactor power

Rod internalpressure

Test FK-10 (61GWd/t BWR)

Peak fuel enthalpy: 359J/g (86cal/g)no fuel failure

Test TK-10 (46GWd/t PWR)

Time (s)

Detachment of strain gage

Cladding strains at failurePeak strain measured at 70-80cal/g was below 0.4%.Plastic hoop strain of the cladding failed was 0%.?(Elastic strain< 0.6%)

20 40 60 80 100 1200.0

0.5

1.0

1.5

2.0100 200 300 400 500

Fuel enthalpy (cal/g)

Cla

ddin

g ho

op s

trai

n (%

)

Fuel enthalpy (J/g)

Calculated strain due to pellet thermal expansion

Measured peak strain (by strain gages)

Measured plastic strain

Estimated peak strain from plastic strains

Deformation to cause the failure could be explained by thermal expansion of fuel pellets

JAERI 13

(2) Consequence of the fuel failure(i) Fission Gas Release in RIA Tests

JAERI

Considerable fission gas release during RIA transient was observed.

The release correlates with fuel enthalpy and burnup.

14

0 10 20 30 40 50 60 700

5

10

15

20

25

Fuel burnup (GWd/t)

Fis

sion

gas

rel

ease

(%

)

PWR

BWR

Peak fuel enthalpy about 70 cal/g

Peak fuel enthalpy about 130 cal/g

0 50 100 1500

5

10

15

20

25

Peak fuel enthalpy (cal/g)

Fis

sion

gas

rel

ease

(%

)

PWR

BWR

Burnup about 60GWd/t

Burnup about 45GWd/t

5µm

20µm

(ii) Fuel Fragmentation

Fine fuel fragmentation occurred when rod failed.

Average size of the fragments was smaller in tests at higher fuel enthalpy (as small as 0.04 mm).

Thermal interaction between fragments and coolant caused water hammer in the capsule.

BWR fuel (61GWd/t) test at 377 J/g (90 cal/g)

JAERI

0

5

10

15

20

25

30

35

????

(%)

FK-6 FK-9W

eigh

t Fra

ctio

n (%

)

0

5

10

15

20

25

30

35

????

(%)

FK-6 FK-9W

eigh

t Fra

ctio

n (%

)3535

Average 43, 81µm

Diameter < 0.026 0.026 0.07 0.122 0.4 0.51 1.02 >2.02(mm) 0.07 0.122 0.24 0.51 1.02 2.02

0

5

10

15

20

25

30????

(%)

Wei

ght F

ract

ion

(%)

0

5

10

15

20

25

30????

(%)

Wei

ght F

ract

ion

(%)

Diameter < 0.026 0.026 0.07 0.122 0.4 0.51 1.02 >2.02(mm) 0.07 0.122 0.24 0.51 1.02 2.02

BWR fuel (61GWd/t) tests 548 377 J/g(131 90 cal/g)

15

Fuel Behavior Tests under Conditions Simulating BWR Power Oscillations without Scram

BWR fuel test

Burnup: 56 GWd/t4 power oscillationsPeak power: 48kW/mFuel enthalpy: 256 J/g (61 cal/g)

Burnup: 25 GWd/t7 power oscillationsPeak power: 95kW/mFuel enthalpy: 368 J/g (88 cal/g)

High power test

JAERI 16

0

10

20

30

40

50

0 10 20 30Time (s)

Pow

er (k

W/m

)

0

100

200

300

400

500

Fue

l ent

halp

y (J

/g)

0

20

40

60

80

100

0 10 20 30Time (s)

Pow

er (

kW/m

)

0

100

200

300

400

500

Fuel

ent

halp

y (J

/g)

Transient Behavior in Power Oscillation Tests

Clear sign of PCMI (Cladding deformation fuel enthalpy) No plastic nor ratcheting deformation of claddingNo DNB (departure from nucleate boiling) No failure

JAERI 17

Cladding (mid)

Water (top)

Rod power(relative)

0 10 20 30Time (s)

0.0

0.1

0.2

0.5

0.4

0.3

Cla

ddin

g el

onga

tion

(%

)

0

50

100

250

200

150

Tem

pera

ture

(?C

)

High power test (25GWd/t)

Claddingelongation

Cladding Deformation in Power Oscillation & RIA Tests

0 50 100 150 200 2500

1

2

3

4

5

6 0 200 400 600 800 1000

Peak fuel enthalpy (cal/g)

Cla

ddin

g el

onga

tion

(%

) RIA High power

BWR

High power test

BWR fuel test

Thermal expansion ofpellets (MATPRO)

Peak fuel enthalpy (J/g)

Cladding deformation comparable to RIA tests (by PCMI in the two types of transients)

JAERI 18

Fission Gas Releases in Power Oscillation Tests & RIA Tests

0 50 100 150 200 2500

5

10

15

200 200 400 600 800 1000

Peak fuel enthalpy (cal/g)

Fis

sion

gas

rel

ease

(%

)

Peak fuel enthalpy (J/g)

PowerOscillation

RIARIA test with sibling BWR fuel (FK-5)

Power oscillation test of BWR fuel

0

500

1000

1500

2000

0.0 0.2 0.4 0.6 0.8 1.0Relative radius

Tem

pera

ture

() Power oscillation test

RIA test

Lower fission gas release during the power oscillation test?Lower temperature at fuel periphery?Smaller heat-up rate

JAERI 19

Radial temperature distributions at time of enthalpy peaked (Calculated with FRAP-T6)

RIA Tests• Brittle cladding failure occurred in high burnup PWR and BWR fuel tests at

fuel enthalpies as low as 60 cal/g. • Same type of failure occurred in fresh PWR fuel rods with hydrided cladding.

The failure thresholds, however, was higher in fresh fuel tests than irradiated fuel tests, suggesting the irradiation effects for the cladding embrittlement.

• Recent RIA tests with transient cladding hoop strain measurementsuggested that the PCMI failure was caused mainly by thermal expansion of pellets. Contribution of fission gases to the failure seems limited.

• Considerable fission gas release and fine fuel fragmentation were observed in the tests. Consequence of the fuel failure would be influenced by these phenomena which should depend on fission gases and fuel morphology at high burnups.

Power Oscillation Tests• First two tests under conditions of BWR power oscillations without scram

were conducted in the NSRR.• Cladding deformation was caused by PCMI and was comparable to those

observed in RIA tests.• Fission gas release was smaller than that observed in RIA test at a

comparable fuel enthalpy.• One more test in FY 2002 is planned under a condition with expected DNB.

SummaryJAERI 20

Future plan to be continued

Future Tests on High Burnup Fuels

NSRR/RIA Tests• Failure thresholds and its consequences

•Japanese UO2 at 45-65GWd/t (Zirlo, MDA, NDA, Zry-2)•Japanese MOX at 30-45GWd/t (Advanced Thermal Reactor type Zry-2)•European* UO2 at 70-74GWd/t (Zirlo, MDA, NDA, Zry-2)•European* MOX at 49-78GWd/t (Zry-4, Zry-2)

• Tests at high temperature high pressure (HT Tests) conditions, in addition to roomtemperature conditions

Cladding Mechanical Testing• Ring tensile, tube burst, etc.

*in ALPS (Advanced LWR Fuel Performance and Safety Research) program sponsored by METI of Japan

MDA, NDA: Zr-Sn-Fe-Cr-Ni-Nb alloy developed by Japanese fuel vendors

Test fuel rod

Pressure suppression tank

Heater

T initial < 286 ? CP initial < 7 MPa

HT Test

JAERI 21

Test Type

2002 2004 2005 2006 20072003

RIA/RT Test

RIA/HT Test

UO2 Fuel

MOX Fuel

FY

Japanese PWR&BWR PWR 17x17 [60 GWd/t]

MDA, Zirlo, NDA

BWR8x8 [61 GWd/t]9x9 [45-65 GWd/t]

PWR 17x17 [70-74 GWd/t] MDA, Zirlo, NDA

BWR 10x10 [75 GWd/t]European (ALPS)

European (ALPS)

PWR 17x17 [59 GWd/t]BWR 8x8, 9x9 [49-78 GWd/t]

ATR[30-45 GWd/t]

NSRR Test Schedule

NS

RR

Shu

t Dow

n fo

r M

odifi

catio

nPower osc. test

JAERI 22

Eu

rop

ean

Fu

el

Shi

pmen

t to

Japa

n