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Activation Analysis

A comparison between FLUKA and FISPACT

results

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Gabriele FirpoReactor and Safety Dept. Phone: +39.010.655.83.42gabriele.firpo@ann.ansaldo.it

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• Background – The Activation Analysis approach in:

• FLUKA • FISPACT

• Comparison between FLUKA and FISPACT calculations:

• Methodology• Results

• Summary and Conclusions

CONTENT

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DEFINITION

Activation Analysis

In the framework of this presentation, it is intended as, and limited to:

The evaluation of the total activity concentration of a material slab being irradiated by monoenergetic projectile particles.

The evaluation of other physical quantities, related to the «activation analysis» as typically intended, like:• Nuclide inventories at different cooling times;• Corresponding radiation fields following the material activationare actually foreseen as a FLUKA/FISPACT comparison issue, but they are out of scope of the present analysis.

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The Bateman Equations

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THE ACTIVATION ANALYSIS APPROACH IN

FLUKA AND FISPACT

Item FISPACT FLUKA

Method Numerical Solution of Bateman Equations

• Full Monte Carlo approach;

• «Mixed» Monte Carlo/Analytical

solution of Bateman Equations.

Geometry 0-D approach* Full 3-D approach*

Parameters of Bateman Equations

Evaluated Data (EAF libraries)

Evaluated Data / Models**

Limitations No build-upNo self-shielding

No build-up

* = See next slide**= Depending on the projectile type/energy

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• Homogeneous and isotropic irradiating flux;

• No flux attenuation: The effective

volume/mass is just a normalization factor.

• «Real» irradiating flux profile;

• Flux attenuation: The effective

volume/mass and dimensions do impact on the activation results.

Φ

x

0-D approach (FISPACT) 3-D approach (FLUKA)

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In order to compare FLUKA and FISPACT approaches, the problem is:

How to make a 0-D (FISPACT) geometrical approach equivalent to a 3-D (FLUKA) one?

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SOLUTION

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Noting that:• The 0-D (FISPACT) approach is rigid: no «degrees of

freedom» to reproduce any kind of irradiating scenario;• The 3-D (FLUKA) approach lets the user to define any kind

of irradiating scenario; many «degrees of freedom» to define it also «whatever the user likes».

It is then envisaged to:1. Define an irradiating scenario—in principle, as simple as

possible—suitable for the 0-D (FISPACT) approach;2. Define, consequently, the corresponding and equivalent

irradiation scenario in FLUKA.

HOW?

Let’s see a practical example…

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1. Fill the list of parameters to completely define a 0-D irradiation scenario in the FISPACT input files:

• Particle type t and energy E;• Homogeneous and isotropic flux Φ;• Material Mat with Volume V (or Mass M);• Irradiation time(s) Ti;• Cooling time(s) Ci.

2. Fill the equivalent FLUKA/FLAIR «decay» input file as follow:• Define an extended isotropic source of particle t with energy E; the

source region must correspond to the detector region;

• Define the material Mat with volume V in the detector region;• Define the IRRPROFI and DCYTIMES cards with the irradiation

parameters Ti and Ci. In particular, the beam intensity—WHAT(2),(4),(6) of the IRRPROFI card—must be equal to the number of particle/s causing an average total flux equal to Φ. This value can be evaluated by another dedicated FLUKA run with USRTRACK card.

OPERATIVE EXAMPLE

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CONSIDERED SCENARIOS

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Case ID Particle type

Energy Flux Target geom.

Material Irrad. Time

Cooling times

1 Proton 50 MeV 1E8 p/cm2/s

Cylinder (r=1 cm, h=1 µm)

SS316LN 90 days 0 s

2 Proton 20 MeV 1E8 p/cm2/s

Cube (1x1x1 cm3) SS316LN 15 years From 0 s

up to 20y

3 Neutron 50 MeV 1E8 n/cm2/s

Cylinder (r=1 cm, h=1 µm)

SS316LN 90 days 0 s

4 Neutron 50 MeV 1E8 n/cm2/s

Cylinder (r=1 cm, h=50 cm)

SS316LN 90 days 0 s

5 Neutron Thermal 1E8 n/cm2/s

Cube (1x1x1 cm3) Cobalt 90 days 0 s

6 Neutron Thermal 1E8 n/cm2/s

Cube (1x1x1 cm3) SS316LN 15 years From 0 s

up to 20y

Note 2: Only neutrons, protons and deuterons projectiles with energies from 0 up to ~55 MeV can be defined with FIPACT 2010 (many other particle types and higher energies, up to ~1 GeV, are available in FISPACT II by CCFE).

Note 1: Available code versions: FISPACT 2010, FLUKA 2011.2b trial.

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Case ID Total activity concentration [Bq/cm3]

Ratio FLUKA/FISPACT

FLUKA FISPACT

1 3.35E6 1.86E6 1.80

2 See graph in the next slide 0.46 (average)

3 1.55E6 1.22E6 1.27

4 9.92E5 1.22E6 0.81

5 3.47E8 4.72E8 0.74

6 See graph in the next slide 1.83 (average)

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LTS 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

SS316LN Total Specific Activity following 15 years of 20 MeV proton irradiation - proton flux 1e8 p/cm2/s

FISPACTFLUKA

Cooling time [s]

Tota

l Spe

cific A

ctivi

ty [B

q/cm

3]

1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+091.00E+04

1.00E+05

1.00E+06

1.00E+07

SS316LN Total Specific Activity following 15 years of thermal neutron (2.5e-8 MeV) irradiation - neutron flux 1e8 n/cm2/s

FISPACTFLUKA

Cooling time [s]

Tota

l Spe

cific A

ctivi

ty [B

q/cm

3]

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• A methodology to make FISPACT and FLUKA activation calculations comparable has been setup;

• Several test runs have been perfomed, showing compatible results within a factor of a few.

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• The phase space of the irradiation scenario parameters has many dimensions: sensitivity analyses are envisaged to understand/find correlations (if any);

• For example, it is expected that, as the linear dimensions of the material slab increase becoming larger than the mean free path of the projectile particle, the effect of flux attenuation in energy becomes not negligible.

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QUESTIONS? COMMENTS?

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MANY THANKS

FOR YOUR ATTENTION

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