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Decay Heat Uncertainty due to Modeling and Nuclear Data Uncertainties

Germina IlasHenrik Liljenfeldt

Oak Ridge National Laboratory

SCALE Users’ Group Workshop 2017

2 Decay heat uncertainty due to nuclear and modeling data uncertainties SCALE Users Group Workshop, September 28, 2017

Outline

• Background• Decay heat analysis methodology• SCALE validation for spent fuel decay heat analysis• Uncertainty in BWR spent fuel due to modeling data uncertainties


Relevance

• Decay heat in spent fuel is critical for the design, safety, and licensing analyses of spent nuclear fuel storage, transportation, and repository systems

• Estimation of decay heat relies in general on code predictions and on available measurements

• Decay heat measurements can be expensive or impractical for covering the multitude of existing fuel designs, operating conditions, and specific application purposes

• Gap of knowledge is heavily supplemented through computer simulations• Well-validated codes and uncertainty analysis are essential


What is Residual Decay Heat?

• Decay heat generated in spent nuclear fuel = all contributions of recoverable energy released from the decay of radionuclides in fuel after its discharge from the reactor

• Decay heat is driven by the isotopic composition in fuel at the end of irradiation

• Decay heat varies with the decay time after discharge (cooling time)

• Calculation of decay heat can be performed with computational tools that simulate – the nuclide transmutations and decay processes during fuel

irradiation in the reactor– the decay from discharge to a designated cooling time


Methodology for Decay Heat ValidationStep 1 – Generation of ORIGEN cross-section libraries

TRITON ModelDesign Data

Depletion Calc.ORIGEN Library

Libraries

Collection + Documentation


Assembly irradiation and decay history

ORIGEN library

Nuclide contentsDecay heatActivities

Sources and spectra

0 1000 2000 3000 4000 5000

103

104

105

Tota

l dec

ay h

eat (

Wat

ts)

decay time (days)

Methodology for Decay Heat ValidationStep 2 –ORIGEN simulations

ORIGEN


Decay Heat Validation Data (Clab Measurements)


Data

set

No. of

measurements

C/E

mean σ

Residual (W)

mean σ

PWR 71 1.002 0.012 0.57 4.91

BWR 50 0.997 0.024 -0.25 3.36

PWR+BWR 121 1.000 0.017 0.23 4.34

Summary of results

Decay Heat Validation Results (SCALE 6.1.3 / ENDF/B-VII.0)

0 100 200 300 400 500 600 700 8000

100

200

300

400

500

600

700

800

PWRBWR

Cal

cula

ted

deca

y he

at (W

)

Measured decay heat (W)

Calculated vs. measured decay heat


Decay heat residual (calculated – measured)

Histogram plot of decay heat residual

100 200 300 400 500 600 700 800-20

-15

-10

-5

0

5

10

15

20

Ringhals 2Ringhals 3

-2σ measurement uncertainty

Resid

ual (

W)


+2σ measurement uncertainty

2σexp [SKB Report R-05-62, 2006]± 9.2 W (3.7%) at 250 W ± 18.8 W (2.1%) at 900 W

-15 -10 -5 0 5 10 150

5

10

15

20

25

30

Cou

nt

Residual bin (W)

Decay Heat Validation - PWR Results


Decay heat residual (calculated – measured)

Histogram plot of decay heat residual

2σexp [SKB Report R-05-62, 2006]± 4.2 W (8.4%) at 50 W ± 6.2 W (1.8%) at 350 W

50 100 150 200 250-15

-10

-5

0

5

10

15

Ringhals 1Oscarshamn 2

-2σ measurement uncertainty

Resid

ual (

W)


+2σ measurement uncertainty

-15 -10 -5 0 5 10 150

5

10

15

20

25

30

Cou

nt

Residual bin (W)

Decay Heat Validation - BWR Results


Decay Heat Uncertainty Estimation

• Perform decay heat simulations for a measured assembly to estimate– Effect of nuclear data uncertainties – Effect of selected manufacturing and operating

parameters uncertainties

• Compare calculated and measurement data and uncertainties

• Selected assembly has multiple measurements Burnup at discharge 36.9 GWd/MTUAverage enrichment 2.9 wt% 235U 63 fuel rods (4 gadolinia) and 1 water rodCorner rods with smaller diameter


Perturbed Modeling Data• Nuclear data (cross sections and fission yields)• Modeling parameters

– Fuel design data

– Operating data

Parameter 1 σ Units

Parameter 1 σ (%)


Computational Model and Tools

SAMPLER – TRITON depletion500 samples for each perturbed set

ORIGEN – decay only

Post-processing, analysis


Assembly Decay Heat

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

% to

tal d

ecay

hea

t

cooling time (years)

am241 pr144 rh106 cs134 eu154 cm244 pu239 pu240 sr90+y90 ba137m+cs137 pu238

Nuclide contribution to assembly decay heat vs. cooling time


Effect of Uncertainty in Fuel Design and Operating Data

177 178 179 180 181 182 183 184 185 186 187 188 189 1900

50

100

150

200

250Operating data

mean=183.35 W 1σ=1.56 W

Assembly decay heat (W)

Cou

nt

177 178 179 180 181 182 183 184 185 186 187 188 189 1900

50

100

150

200

250mean=182.83 W 1σ=0.37 W

Fuel data


Cou

nt

Histogram of calculated decay heat variation at time of measurement


Effect of Uncertainty in Nuclear Data

177 178 179 180 181 182 183 184 185 186 187 188 189 1900

50

100

150

200

250


mean=183.28 W 1σ=1.62 W

Cross section data

Cou

nt

Histogram of calculated decay heat variation at time of measurement

177 178 179 180 181 182 183 184 185 186 187 188 189 1900

50

100

150

200

250


mean=183.08 W 1σ=0.47 W

Fission yield data

Cou

nt


Uncertainty in Major Contributors to Decay Heat at Measurement Time

ba137m y90 pu238 cm244 am2410.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

isot

ope

mas

s un

cert

aint

y (%

)

operating data design data cross-section data fission yield data

ba1

37m

y90

pu

238

cs13

7

cm24

4

am24

1

sr90

pu

240

eu15

4

pu

239

cs13

4

0

5

10

15

20

25

30

dec

ay h

eat

con

trib

uti

on

(%

)


Decay Heat Uncertainty vs Burnup and Cooling Time

2.01.81.6

1.41.2

1.0

0 10 20 30 40 50 60 70 80 90 1005

10

15

20

25

30

35

burn

up (G

Wd/

MTU

)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

uncertainty (%)

0.4

0.3

0.2

0.1

0 10 20 30 40 50 60 70 80 90 1005

10

15

20

25

30

35

burn

up (G

Wd/

MTU

)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

uncertainty (%)

Fuel data perturbationOperating data perturbation


Decay Heat Uncertainty vs Burnup and Cooling Time

Fission yield data perturbationCross-section data perturbation

0.9 1.1

1.0

0.90.8 0.7

0.6

0.5

0.4

0.3

0.2

0 10 20 30 40 50 60 70 80 90 1005

10

15

20

25

30

35bu

rnup

(GW

d/M

TU)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

uncertainty (%)

0.4

0.3

0.2

0 10 20 30 40 50 60 70 80 90 1005

10

15

20

25

30

35

burn

up (G

Wd/

MTU

)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

uncertainty (%)


Conclusion• SCALE/ORIGEN has well-established, well-validated capabilities for spent fuel M&S,

including evaluation of uncertainties in calculated decay heat due to both modeling and nuclear data uncertainties

• Calculated decay heat agrees well with measurement data for PWR and BWR– average C/E is 1.002 (σ =0.012) for PWR and 0.997 (σ =0.024) for BWR

• Uncertainty in calculated decay heat – dominated by uncertainty in cross-section data (σ= 0.9%) and operating data (σ= 0.8%) – small effect of uncertainty in fuel data (σ= 0.2%) and fission yield data (σ= 0.3%)

• Decay heat uncertainty values are driven by uncertainty in isotopic masses of a handful of important decay heat contributors

• Uncertainty in calculated decay heat (separate effects) is comparable to measurement uncertainty (σ= 0.9%) for this assembly

• Quantifying uncertainty can provide useful information and inform decisions on design and operation of spent fuel storage facilities, particularly in regimes where measurement data are not available or are not practical to obtain.


References

• G. Ilas and H. Liljenfeldt, "Decay heat uncertainty for BWR used fuel due to modeling and nuclear data uncertainties”, Nuclear Engineering and Design, vol.319, p. 176-184 (2017) https://doi.org/10.1016/j.nucengdes.2017.05.009

• Williams, M., G. Ilas, M. A. Jessee, B. T. Rearden, D. Wiarda, W. Zwermann, L. Gallner, M. Klein, B.Krzykacz-Hausmann, and A. Pautz, 2013. A statistical sampling method for uncertainty analysis with SCALE and XSUSA, Nuclear Technology, vol.183, no.3, p 515-526 (2013). http://dx.doi.org/10.13182/NT12-112

• G. Ilas, I. C. Gauld, and H. Liljenfeldt, "Validation of ORIGEN for LWR used fuel decay heat analysis with SCALE”, Nuclear Engineering and Design, vol.273, p. 58-67 (2014) https://doi.org/10.1016/j.nucengdes.2014.02.026

https://doi.org/10.1016/j.nucengdes.2017.05.009

http://dx.doi.org/10.13182/NT12-112

https://doi.org/10.1016/j.nucengdes.2014.02.026


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