loca analysis
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C. GRANDJEANIRSN, Cadarache
NRC / IRSN Meeting, Bethesda, January 24-26, 2007
LOCA Analysis-----------
Physical Phenomenato be Taken into Consideration
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 2/11
FUEL RELOCATION
HIGH PRESSURE OXIDATION
SECONDARY HYDRIDING IN HIGH BU BALLOONED CLADDING
OXYGEN DIFFUSION FROM AN INITIAL OXIDE LAYER
Physical Phenomena to be Taken into Consideration
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 3/11
FUEL RELOCATION
Fuel relocation occurrence during LOCA is widely admittedas it has been observed in all burst tests with irradiated fuel rods
FR2 results
ANL integral test
HALDEN IFA-650
PBF/LOC (INEL)
FR-2 (KFK)
FLASH-5 (CEA)
ANL ICL-2 results
At low and medium burn-up : At high burn-up :
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 4/11
FUEL RELOCATION
Halden IFA-650.4
extended relocation of fuel
in the balloon and out of the test rod
Potential impact on clad balloon :
- increase of PCT and maximum ECR
Potential consequences of fuel dispersal :
- increase in radiological release
- possible impact on the integrity of structural materials
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 5/11
FUEL RELOCATION Pending issues (1)
Instant of relocation
close to burst time (FR-2/E3 and E4 tests, Halden IFA-650.4)
Filling ratio of clad balloon
Few available data from PBF/LOC and FR-2
Expected data from HALDEN/IFA-650 tests
What is the impact of fuel micro-structure ?MOX or Gd fuel (High BU structures)Doped fuel (-> in EPR)
Properties of relocated fuel
Granulometry : Expected data from HALDEN
Thermal conductivity
Heat exchange between clad and fuel fragments
Balloon filling rate (%) by relocated fragments
20 30 40 50 60 70 80Ballooning (%)
PBF/LOC-gammascanningPBF/LOC-micrographiesFR-2Upper boundIRSN sensitivity calculation
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IRSN reference calculation
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 6/11
FUEL RELOCATION Pending issues (2)
Main consequences of the relocation process
Local increase in lineic and surfacic powers
Local decrease in fuel/clad gap (heat transfer increase)
Modification of steam access to the balloon inside
What is the impact of these consequences
On coolability around balloonned region with fuel relocation
On peak clad temperature and final oxidation ratio ?
On hydrogen uptake and consequences for quenching and post-quench embrittlement ?
EASY NOT SO EASY
these questions are particularly important for end-of-life MOX fuel
for which power generation is not reduced, unlike for UO2 fuel !
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 7/11
FUEL RELOCATION Calculations
Few studies published on the impact of relocation under LB LOCA conditions
Bergquist et. al (1978-79) ; INEL (1981) : limited simulation of PBF/LOC results
IRSN (2004) : sensitivity studies with CATHARE-2 code
IRSN (2006) : simulation of IFA-650.4 test with ICARE-CATHARE code
Assumptions on parameters
Filling ratio of the balloon
Thermal conductivity of fuel fragments
Heat transfer coef. fuel fragments / clad
Main results
Increase of PCT and ECR
Decrease of Zr-β layer thickness
High sensitivity to filling ratio
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 8/11
HIGH PRESSURE OXIDATION
Data base of results :
(Pawel et al., Park et al., Bramwell et al., Vrtilkova et al.)
from the existing results, the increase in oxidation kinetics (weight gain and layers thickness growth) remains moderate (factor < 2) in the SB LOCA pressure range (< 50 bar) and should not make an additional issue,
providing that the hydrogen absorption does not increase significantly
However, secondary hydriding in HP conditions has not yet been investigated
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 9/11
SECONDARY HYDRIDING IN HIGH BU BALLOONED CLADDING
ECR and H profiles in unirradiated rod OCL#11 ECR and H profiles in irradiated rod ICL#3
The peaks of hydrogen absorption appear located nearer the burst opening in irradiated rods, likely in relation to local optimal S/V values on clad inner side after fuel relocation, promoting H pickup.
Need to better quantify the hydrogen pickup axial profile in view of evaluating the embrittlementconditions in and around the ballooned regions
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 10/11
OXYGEN DIFFUSION FROM AN INITIAL OXIDE LAYER
At temperatures ≤1000 °C, oxygen diffusion through the monoclinic oxide is slower than oxygen diffusion into the metal. Therefore, an initial pre-oxide layer may partially dissolve in the underlying prior β-Zr, and result in clad embrittlement, before a significant rise of the transient ECR
Residual ductility ( 900°C )
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ECRCath-Paw [%]
Res
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2 um A1 2 um A210 um A1 10 um A235 um A1 45 um A2
(V. Vrtilkova, SEGFSM Meeting, Paris, April 2005)
Pre-oxidised standard ASTM Zircaloy-4 (950°C)
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ECRCath-Paw [%]
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0 µm 2 µm 10 µm 50 µm
C. Grandjean NRC / IRSN Meeting, January 24-25, 2007 11/11
OXYGEN DIFFUSION FROM AN INITIAL OXIDE LAYER
An appropriate simulation of the partial dissolution of the initial oxide scale requires the calculation of O diffusion within the moving-boundary system, with taking account of the different diffusion properties in the dual phase (monoclinic/tetragonal) oxide
Such calculational tool is under development at IRSN (DIFFOX code)
900 C (35 um, 600 wppm H2)
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Time [s]
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1/1 Dx ZrO21/2 Dx1/3 Dx1/1 Dx Alpha1/2 Dx1/3 DxExp ZrO2Exp Alpha
α-Zr(O)
ZrO2 12
3
Simulation of an UJP test with the DIFFOX code
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