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7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
1/16
Instit
uteofIso
topes
HungarianAcademyofScien
ces
1
Gamma spectrometry for burnupdetermination of spent fuel assemblies at
the NPP Paks
I. Almasi, Z. Hlavathy, C. T. Nguyen, P. Nagy, L. Lakosi, T. Parko and I. Pos
TECHNICAL MEETING
ONHOT CELL POST-IRRADIATION EXAMINATION AND POOL-SIDE
INSPECTION OF NUCLEAR FUEL
23-27 May 2011
Smolenice, Slovakia
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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Instituteo
fIsotopes
HungarianAcadem
yofsciences
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Goal
Develop a method for determining the burnup of theassemblies.
Validate the calculation of burnup from the reactor
parameters
Should be independent measurement method
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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yofsciences
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Why is the measurement important?
If the results of the measurement correspond withcalculated values, the safety margin could be
decreased in the calculation, thus the assemblies
could be used for higher power output
Could be cecked anomalies in the core
Safeguards aspect more precise values
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Method description
Production of Cs-137 is linearly proportional to theneutron fluence, i.e. the number of U-235 fissiled.
Cs-134 is produced in two steps: the fission product
Cs-133, then, by neutron capture Cs-134
direct Cs-134 production from fission is of lowerprobability by orders of magnitude.
The production of Cs-134 is proportional almost the
square of neutron flux.
If the activity of Cs-134 and Cs-137 is known, theburnup can be calculated as
BU= k(ACs-134/ACs-137)
K calculated from reactorphysic parameters
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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Method description (cont.)
Why not used directly the activity of Cs-137?
CountrateCs-137(662 keV)=
ACs-137*Ig*f(AbsU)*f(Abscm)*f(Absw)*f(Abscol)*R-2*Deteff
well known or measurable
calculated good precision/can be only estimated.
The Cs-134 has two strong peaks 605 keV, Ig=97.6%,and 796 keV, Ig=85.5%.
The Cs-137 has one peak at 662 keV, Ig=85.1%
Peeks of Cs-134 determined the relative efficiency ofdetection the 662 keV gamma by intrinsic calibration
In this way the geometry dependent parameters will beeliminated
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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HungarianAcadem
yofsciences
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Equipment
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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HungarianAcadem
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Dependence of Cs ratio on the distance
y = 4E-05x + 0,5108
0,500
0,600
0,700
0,800
2700 2800 2900 3000 3100
Coordinate (mm)
Cs-134/Cs-137ratio
Only 1% changes at used measuring distance
Cs-134/Cs-137 activity ratio vs. distance
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Measurements
Four assembly groups /6 assemblies, as the core isdivided into 6 sectors same position in each sector
High burnup (44GWd/tU)
Low burnup (10GWd/tU)
39GWd/tU burnup 3,8% initial enrichment
26GWd/tU burnup 2,4% initial enrichment Two control assemblies
Two the neighbor of control assemblies
Altogether 28 assemblies were measured
Scanning of the assemblies of all the 6 sides 5-12 positions by side
measured ~1200 spectra 300-600s each
Took 5 weeks
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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HungarianAcadem
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Measurements
Burnup profile
0,2
0,3
0,4
0,5
0,6
0,7
1800 2300 2800 3300 3800 4300
vertical coordinate (mm)
Cs-134/Cs-137
ratio
A typical burnup profile and its measured points
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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Results
69260
0
0,25
0,5
0,75
11
2
3
4
5
6
69235
0
0,25
0,5
0,75
11
2
3
4
5
6
69249
0
0,25
0,5
0,75
11
2
3
4
5
6
69261
0
0,25
0,5
0,75
11
2
3
4
5
6
69248
0
0,25
0,5
0,75
11
2
3
4
5
6
69275
0
0,25
0,5
0,75
11
2
3
4
5
6
Azimuthal profiles of 39 GWd/tU
group at the center of pins
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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69249
0,5
0,6
0,7
0,8
0,9
1
1,1
1800 2300 2800 3300 3800 4300Vertical coordinate (mm)
Cs-1
34/Cs-1
37
-180
-120
-60
0
60
120
Burnup profile of a working fuel assembly
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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67835
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
1800 2300 2800 3300 3800 4300
Vertical coordinate (mm)
Cs-1
34/Cs
-137
-180
-120
-60
0
60
120
Burnup profile of a control fuel assembly
7/31/2019 1.3. ALMASI Gamma Spectrometry for Burnup Determination of Spent Fuel Assemblies at the Paks NPP
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67753
0,1
0,3
0,5
0,7
1800 2300 2800 3300 3800 4300
Vertical coordinate (mm)
Cs-134/Cs-137
calc. (-180)
meas. (-180)
calc. (-120)
meas. (-120)
calc. (-60)
meas. (-60)
calc. ( 0)
meas. ( 0)
calc. ( 60)
meas. ( 60)
calc. ( 120)
meas. ( 120)
The Cs-134/Cs-137 ratio from measurements and calculation
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Measured vs. calculated isotop activity ratio Cs-134/Cs-137
y = 1,0149xR
2= 0,9955
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8
Calculated ratio
Measuredratio
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Summary
By this method the burnup of assemblies can bedetermined.
Uncertainty of the method is around 4%. To decreasethe uncertainty the measurement time should beincrease by decreasing the number of measured
positions and/or assemblies. For the best results 2-4 years old assemblies should
be measured.
The method should be checked at other ponds in NPP
Paks first. Its also planned to modify the detector system to
measure ponds without built in collimator, to be ableuse the method for other reactors too.
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Thank You for Your attention!
www.iki.kfki.hu