ANALYSIS OF CABRI DRIVER CORE NEW SAFETY DEMONSTRATION FOR FUEL - - PowerPoint PPT Presentation

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ANALYSIS OF CABRI DRIVER CORE NEW SAFETY DEMONSTRATION FOR FUEL RODS INTEGRITY DURING FAST POWER TRANSIENTS F. Ecrabet, C. Pelissou, A. Moal IGORR 12, Beijing, China October 20 th , 2009 IRSN : technical support of the French Nuclear Safety

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SLIDE 1

ANALYSIS OF CABRI DRIVER CORE NEW SAFETY DEMONSTRATION FOR FUEL RODS INTEGRITY DURING FAST POWER TRANSIENTS

  • F. Ecrabet, C. Pelissou, A. Moal

IGORR 12, Beijing, China October 20th, 2009

S ystème de management de la qualit é IRS N certifié

IRSN : technical support of the French Nuclear Safety Authority

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IGORR 12, Beij in, China, 30 October 2009 Page 2

CABRI reactor

DRIVER CORE

  • Power of 25MW cooled with water in

forced convection

  • Enriched UO2 fuel rods, 6%

in 235U, stainless steel cladding material, fissile zone = 60 x 60 x 80 cm,

  • 6 control and safety rods
  • 4 transient rods (gaseous absorber rods –

Helium 3) EXPERIMENTAL LOOP

  • Located at the center of the driver core
  • Fast power transients simulated by nuclear

pulses

  • 3 $ of mean increasing reactivity with a

50 $/ s ramp

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SLIDE 3

IGORR 12, Beij in, China, 30 October 2009 Page 3

Outline

  • IRSN assessment of new CABRI driver core safety

criteria

  • SPERT and NSRR integral experiments
  • Conclusion
  • Comparison of the new CABRI criteria to integral

experiments

 Thermomechanical simulations : SCANAIR code

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IGORR 12, Beij in, China, 30 October 2009 Page 4

CABRI driver core new safety criteria

  • CEA criteria
  • IRSN approach

Two possible failure modes of the clad

  • Clad melting
  • Ductile rupture

Past experiments

  • Realized in S

PERT and NS RR facilities on fuel rods similar to CABRI ones

  • S

ingle fuel rod submitted to very short power transients

  • Identify the failure threshold as a

maximum inj ected energy To warrant the cladding integrity of the driver core during future tests :

  • Maximum clad temperature set to

1300°C (margin of 150°C to the melting temperature of the stainless steel cladding material)

  • Maximum clad hoop strain must be

lower than 3.65% (50%

  • f the lowest

value of the rupture elongation measured on samples representative

  • f the clad)
  • Fuel melting not allowed : maximum

fuel temperature should remain below 2800°C Comparison of the new criteria with this failure threshold

  • Use of S

CANAIR code

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SLIDE 5

IGORR 12, Beij in, China, 30 October 2009 Page 5

Integral experiments

  • SPERT experiments : description (United States 1960-70)
  • Many types of unirradiated UO2 fuel rods tested; among them 2

tests series with rods similar to CABRI ones (F-type and SPX)

  • Single power burst

 Objective : determine the approximate injected energy

(given at the axial flux peak) in fuel rods required to cause clad failure

0.05 800 He 800 0.025 460 He 530 0.076 910 He 1060

Fuel rod

Pellet-cladding gap (mm) Fuel lengt h (mm) Plenum gas Overall length (mm) Al Si 304-SS 10.0 0.4 304-SS 6.35 0.356 304-SS 11.84 0.508

Cladding

Material Outer diameter (mm) Wall thickness (mm) 9.19 11.5 94 6 Chamfered 5.59 11.4 95 3 / 10 flat 10.67 15.2 92 4.8 flat

UO2 pellet

Diameter (mm) Lengt h (mm) Density (% T.D.) Enrichment (% ) End shape

CABRI driver fuel rod SPX fuel rod F-type fuel rod Characteristics

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SLIDE 6

IGORR 12, Beij in, China, 30 October 2009 Page 6

Integral experiments

  • SPERT experiments : results

 7 fuel rod tests out of 54 had failed

[200, 570] [50, 300] Injected energy (cal/g) 7 47 Number of tests Fuel rod type SPX Fuel rod type F-type

  • Failure mechanism : mainly cladding melting
  • Important cladding oxidation of failed rods
  • Failure threshold for stainless steel clad rods :

[244, 278] cal/g with reactor period [3ms, 6ms]

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IGORR 12, Beij in, China, 30 October 2009 Page 7

Integral experiments

  • NSRR experiments : description (Japan 1970)
  • Same conditions as SPERT

 Objective :

  • study different fuel rods behavior during fast power transients
  • define an injected energy failure threshold for each type of

rod

0.05 800. He 0.5 800. 0.095 135. He 0.1 279.

Fuel rod

Pellet-cladding gap (mm) Fuel lengt h (mm) Plenum gas (MPa) Overall length (mm) Al Si 304-SS 10. 0.4 304-SS 10.53 0.40

Cladding

Material Outer diameter (mm) Wall thickness (mm) 9.19 11.5 94. 6. Chamfered 9.54 10. 94.4 10. Chamfered

UO2 pellet

Diameter (mm) Lengt h (mm) Density (% T.D.) Enrichment (% ) S hape

CABRI driver fuel rod stainless steel clad fuel rod Characteristics

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SLIDE 8

IGORR 12, Beij in, China, 30 October 2009 Page 8

Integral experiments

  • NSRR experiments : results
  • 10 tests were conducted with injected energies

ranging from 114 to 457 cal/g

Oxygen-induced embrittlement Cladding melting Failure mechanism (same test condition) 260 [221, 258] => 240 Failure threshold energy (cal/g) Zircaloy clad fuel rod S tainless steel clad fuel rod NS RR results

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IGORR 12, Beij in, China, 30 October 2009 Page 9

Discussion : Integral experiments

  • Integral experiments (S

PERT&NS RR) were used to define failure criteria based on inj ected energy in rod during transient

  • Characteristics of the rods close to those of CABRI reactor rods (UO2

fuel, stainless steel clad)

  • Thermal hydraulic conditions were similar : stagnant water at ambient

temperature, atmospheric pressure

  • Difference on pulse width : 5ms (NS

RR) < 10ms (CABRI) < 20ms (S PERT)

  • The obtained results are consistent between the 2 studies
  • Identified failure mechanism : cladding melting

240 cal/g [244, 278] cal/g Failure threshold energy NSRR study Failure threshold energy SPERT study

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SLIDE 10

IGORR 12, Beij in, China, 30 October 2009 Page 10

SCANAIR IRSN Code

Input data

  • Irradiation software
  • Characterization

examinations

  • Power pulse

Thermal behavior Mechanics Fission gases Gap width

  • r contact

pressure

Temperature

Hydrostatic pressure S welling strain Fission gas release Temperature

  • Devoted to thermal mechanical simulation of one fuel rod (UO2 or MOX) during

fast power transient (RIA)

  • Qualified on integral tests performed in CABRI reactor, NS

RR reactor and PATRICIA CEA thermal hydraulic facility

  • Three implicitly coupled modules

DESCRIPTION

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IGORR 12, Beij in, China, 30 October 2009 Page 11

SCANAIR IRSN Code

free volumes : plenum, gap fuel clad coolant loop shroud

10 cm to 4 m

  • Fuel rod in a fluid channel
  • Pellet and clad fine meshed axially and radially

Example of temperature field in fuel rod

GEOMETRY MODELISED BY SCANAIR

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IGORR 12, Beij in, China, 30 October 2009 Page 12

Comparison of new CABRI criteria to integral experiments

CABRI DRIVER CORE FUEL ROD CALCULATIONS

  • Only 10ms power transients are considered (most penalizing case)
  • Three calculations performed with different sets of hypothesis (uncertainties on

power, rod geometry, physical properties… )

  • to maximise clad temperature (clad temperature criterion)
  • to maximise clad strain (clad hoop strain criterion)
  • Best-estimate
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IGORR 12, Beij in, China, 30 October 2009 Page 13

CALCULATIONS TO REACH THE NEW SAFETY CRITERIA

287 cal/ g Clad hoop strain = 3.65% 246 cal/ g Fuel temperature = 2800°C 236 cal/ g Clad temperature = 1300°C Inj ected energy 10 ms pulse

Comparison of new CABRI criteria to integral experiments

T=860°C | eps=1.36% eps=2.50% T=1274.1°C Maximum values 195 cal/ g Best-estimate calculation 231 cal/ g Conservative calculation (clad strain) 231 cal/ g Conservative calculation (clad temperature) Inj ected energy 10 ms pulse

  • Cladding melting comes

first

  • S

afety criteria proposed by CEA in the same range as the limit found in the past, based on integral experiments

  • Tuning power to reach the criteria values

MOST SEVERE TEST FORESEEN IN CABRI

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IGORR 12, Beij in, China, 30 October 2009 Page 14

Conclusion

 CEA proposed an innovative analytical approach to insure the

cladding integrity of the CABRI driver core

  • S

et limits of physical values representative of the fuel rod failure mode

 IRSN used an integral approach based on past experiments (NSRR

and SPERT facilities)

  • Identify a failure threshold energy for stainless steel clad fuel rods

similar to CABRI ones

  • Comparison of this threshold to CEA criteria thanks to S

CANAIR computations

 This study shows the consistency of new criteria with the failure

limit of past integral experiments

  • It constitutes one of the important items which leads French

Nuclear Safety Authority to accept the safety demonstration of the driver core fuel rods for the new experimental program in CABRI facility

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IGORR 12, Beij in, China, 30 October 2009 Page 15

Thank you for your attention

Fabrice ECRABET fabrice.ecrabet@irsn.fr +33 1 58 35 79 07