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Evaluation of creep during dry storage in low and high burnup fuels

F. Feria, L.E. Herranz CONTENTS 1.

2.

3.

4.

Motivation and objective Extension of FRAPCON-3.3 creep law Creep assessment Final remarks Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

1. MOTIVATION AND OBJECTIVE

Safety objectives:

-

Radiation dose Subcriticality Confinement Retrievability Cladding integrity Degrading mechanisms IAEA meeting SCC Creep DHC Evaluation in low and high burnup Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

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2. EXTENSION OF FRAPCON-3.3 CREEP LAW

In-FRAPCON modelling

 i   i e   i p  d  i p   i T i   , z , r d  p  c  dt

Creep law:

  c  4  c ( f 1 (   )· f 2 ( T )· f 3 (  )) 2

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f 1 (   )     725.2

exp( 4.967·10 -8   ) f 2 ( T )  exp(  10000 / RT ) f 3 (  )  5.129·10 -29 

Vienna (Austria), 31.05-4.06.2010

2. EXTENSION OF FRAPCON-3.3 CREEP LAW

Creep law validity range IAEA meeting Restricted to in-reactor conditions Extension of the creep law is needed to apply the code to dry storage conditions Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

2. EXTENSION OF FRAPCON-3.3 CREEP LAW

Zircaloy-4 database (EDF) IAEA meeting Generic correlation Nuclear Safety Research Unit

 c   c p   c s  i c  f 1 i (   )· f 2 i ( T )· f 3 i (  t )· f 4 i ( t ) i  p , s

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2. EXTENSION OF FRAPCON-3.3 CREEP LAW

CIEMAT creep law

  f 1 (   )· f 2 ( T )· f 3 (  t )· t  0 .

5 f 1 (   f 2 ( T ) )  a 2  b   exp   T   c 273   f 3 (  t )  exp(  d ·  t )

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2. EXTENSION OF FRAPCON-3.3 CREEP LAW

CIEMAT creep law

0.2

CIEMAT EDF 0.1

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0 0 200 400

t(h)

600 800 1000 0.3

0.2

0.1

CIEMAT EDF 0.0

0 100 200 300

t(h)

400 500

Vienna (Austria), 31.05-4.06.2010

600

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2. EXTENSION OF FRAPCON-3.3 CREEP LAW

Implementation Together with a suitable logic that allows choosing between the “in-reactor” equation and the dry storage equation, according to the prevailing conditions at the calculation time The extension splits in two hoop stress ranges:

  

≥ 121 MPa → Creep law parameters derived from irradiated claddings data

  

≤ 121 MPa → Creep law parameters derived from non-irradiated claddings data No experimental data is available with irradiated material under low hoop stress Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

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3. CREEP ASSESMENT

40 35 30 25 20 15 10 5 0 0

Postulated scenarios a) Zircaloy-4 45 GWd/tU

500 1000

t(days)

1500 2000 0.8

0.6

0.4

0.2

0.0

0

Nuclear Safety Research Unit 1º) In-reactor irradiation 2º) Pool storage (1 year) 3º) Dry out (1 day) 4º) Dry storage (2 years)

200

Phases

400

t(days)

600 800 35 30 25 20 15 10 5 0 0 500

b) Zircaloy-4 63 GWd/tU

1000

t(days)

1500 2000 2500

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Trillo

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3. CREEP ASSESMENT

Results

0.2

0.1

0 -0.1

-0.2

-0.3

-0.4

-0.5

-0.6

-0.7

-0.8

0 400

a) Zircaloy-4 45 GWd/tU

In-pool cooling Dry storage Trillo2 800 1200

t(days)

1600 2000 2400 1.5

1 0.5

0 -0.5

-1 0 400 800

b) Zircaloy-4 63 GWd/tU

In-pool cooling Dry storage 1200

t(days)

1600 

Once dry storage starts hoop stress causes a creep-out situation

2000 2400

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3. CREEP ASSESMENT

Results

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 45 GWd/tU 63 GWd/tU 100 200 300 400

t(days)

500 600 700 800 

The creep main impact would take place during the first months



In no case creep reaches 1 % strain limit



Nearly 4 times higher hoop strain as burn-up is increased by 40 % Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

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4. FINAL REMARKS



High burn-up effect seems substantial and causes major differences in the nuclear fuel response in terms of creep



The results would have a conservative nature because the irradiation hardening effect is not considered at low stresses



Further work:

•

Extend CIEMAT creep law to irradiated fuel rods submitted to low stresses

•

Extend the study up to 100 years to estimate the final creep asymptotic value Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

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ACKNOWLEDGMENTS

The authors are indebted to ENRESA for their financial support and the technical discussions held and to the FRAPCON-3 developers for their technical support during this work Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010

IAEA meeting THANK YOU FOR YOUR ATTENTION Nuclear Safety Research Unit Vienna (Austria), 31.05-4.06.2010