TAPIRO fast spectrum research reactor for neutron radiation damage - - PowerPoint PPT Presentation

• M. Carta*, K. W. Burn, P. Console Camprini, V. Fabrizio, L. Falconi, A. Santagata

(ENEA – Italy)

• S. Dulla, P. Ravetto

(Politecnico di Torino – Italy)

*mario.carta@enea.it

TAPIRO fast spectrum research reactor for neutron radiation damage analyses

IGORR 18 3-7 December 2017, Sydney Australia

IGORR 18 3-7 December 2017, Sydney, Australia

Layout of the presentation

2

1. Introduction 2. ASTM standard damage functions 3. The TAPIRO reactor 4. TAPIRO neutronic characterization 5. TAPIRO damage parameters 6. Roundup

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Introduction

• Although Material Testing Reactors (MTRs), having powers greater than 5÷10 MW, are

usually selected as radiation fields for neutron radiation damage analysis, nowadays an increasing attention is paid also to low power research reactors because they can provide very qualified, in terms of both intensity and energy spectrum, neutron radiation fields.

• The ENEA low power fast spectrum TAPIRO research reactor, located in the Casaccia

Research Center near Rome, Italy, complies with the above quality requirements.

• This paper describes how the neutron flux characterization has been performed in the

past at TAPIRO.

• Characteristics of some main ASTM standard damage parameters, such as 1 MeV

equivalent neutron flux and hardness parameter, are provided for different positions along the main irradiation channels.

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A A A A A A A A A

En Rate of displacements produced by a Primary Knock-on Atom (PKA) after elastic (for example) collision with neutrons having energy En PKA

ASTM standard damage functions The damage mechanism

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A A A A A A A A A

En

) E (

n el



) E ( ) E ( ) E ( dpa

n n el n

   

ASTM standard damage functions The damage mechanism

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A A A A A A A A R

T             

n 2 n

E ) A 1 ( A 4 E T

   

        cos 1 E ) A 1 ( A 4 2 1 cos 1 E 2 1 T

n 2 n

n

θ

ASTM standard damage functions The damage mechanism

) E ( ) E ( ) E ( dpa

n n el n

   

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0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 50 100 150 200 250 <T>/En A

Mean transferred energy <T> to an atom by elastic collision with a neutron having energy En

ASTM standard damage functions The damage mechanism

IGORR 18 3-7 December 2017, Sydney, Australia

average threshold displacement energy for an atom

8

T

D

d

E

A A A A A A A R

d d

E 2 T E  

) E ( ) E ( ) E ( dpa

n n el n

   

ASTM standard damage functions The damage mechanism

IGORR 18 3-7 December 2017, Sydney, Australia

average threshold displacement energy for an atom

9

T

D

) T ( 

d

E

A A A A A A R D

d

E 2 T  …

 

dT ) T ( T ; E P ) E ( ) E ( ) E ( dpa

n E E n n el n

n d

       





ASTM standard damage functions The damage mechanism

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                

n d d d d d

E T E 8 . 2 for E 2 T 8 . E 8 . 2 T E for 1 E T for ) T (

0.0 5.0 10.0 15.0 20.0 25.0 0.00E+00 2.00E+02 4.00E+02 6.00E+02 8.00E+02 1.00E+03 1.20E+03 1.40E+03 ν (T ) T (eV)

ν (T)

En = 1 keV En = 10 keV

ASTM standard damage functions The damage mechanism

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An approximate relation is:

11

t E 4 E ) t ( dpa

el d n

          

For example, assuming for 27Al <σel> = 3 barn, <En> = 0.5 MeV, Ed = 25 eV, Δt = 1 year we

• btain the figure below for different flux intensities.

0.01 0.10 1.00 10.00 100.00 1.00E+11 1.00E+12 1.00E+13 1.00E+14 1.00E+15 dpa*year φ (n∙cm-2∙s-1)

JHR 100 MW TRIGA 1 MW

ASTM standard damage functions The damage mechanism

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In general a PKA will generate a cascade of ν displacements. This cascade will deposit in the lattice a damage energy ED(T), also indicated as partition energy, proportional to the PKA energy T, given by:

12

) T ( L T ) T ( ED  

where L(T) is the Lindhard partition function. It can be defined a displacement KERMA (Kinetic Energy Released in MAterials) function (units [barn∙eV]) for neutron collisions. This function FD provides the rate, following neutron collisions, of deposit in the lattice of a damage energy ED(T), for unit atom and unit flux.

eV] [barn dT ) T ( L T ) T ; E ( P ) E ( ) E ( F

n n el n D

     



ASTM Standards

ASTM standard damage functions KERMA functions

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1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Fd (mb·MeV) E (eV)

28Si Damage functions

JANIS JEFF 3.1 ASTM

ASTM standard damage functions KERMA functions

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In general we’ll have for a certain neutron flux, being N the atomic density of the material:

14

where wD is the rate, following neutron collisions, of deposit in the lattice of the damage energy density. wD has units [eV∙cm-3∙s-1]. It can be noticed that wD is a “damage” power

• density. For an interval time Δt we have:

] s cm [eV dE ) E ( ) E ( F N w

• 1
• 3

n n n D D

      ] cm [eV dE ) E ( ) E ( F t N D

• 3

n n n D

     



ASTM standard damage functions KERMA functions

IGORR 18 3-7 December 2017, Sydney, Australia

For a certain position of the system we can define a monochromatic flux with energy Eref given by : having the properties to produce the same damage power at the same position of the system: This flux it’s named the Eref equivalent flux. In particular, if Eref=1 MeV, we’ll have: Or: and this flux it’s named the 1 MeV equivalent flux.

15

) E E ( ) E , (

ref n n eq

   r

n n n D D ref eq ref D ref , eq , D

dE ) E , ( ) E ( F ) ( W ) E , ( ) E ( F ) ( W r r r r       



n n n D eq D

dE ) E , ( ) E ( F ) MeV 1 , ( ) MeV 1 ( F r r     



) MeV 1 ( F dE ) E , ( ) E ( F ) MeV 1 , (

D n n n D eq

r r    



ASTM standard damage functions 1 MeV equivalent flux

IGORR 18 3-7 December 2017, Sydney, Australia

We can define a neutron spectrum hardness parameter as:

16 n n eq

dE ) E , ( ) MeV 1 , ( ) ( H r r r   



n n eq

dE ) E , ( ) MeV 1 , ( 1 H r r     



We need less 1 MeV neutrons to produce the same damage produced by the system neutron

• spectrum. The system neutron spectrum tends

to be “softer ” respect 1 MeV eq.

n n eq

dE ) E , ( ) MeV 1 , ( 1 H r r     



The same 1 MeV or system neutron spectrum neutrons are needed to produce the same

• damage. The system neutron spectrum tends

to be “damage analogous” respect 1 MeV eq.

n n eq

dE ) E , ( ) MeV 1 , ( 1 H r r     



We need more 1 MeV neutrons to produce the same damage produced by the system neutron spectrum. The system neutron spectrum tends to be harder ” respect 1 MeV eq.

ASTM standard damage functions Spectrum hardness parameter

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          



k k k

t ) t ( dpa ] s cm [eV dE ) E ( ) E ( F N w

• 1
• 3

n n n k , D k D

    

 

] cm [eV dE ) E ( ) E ( F t N D

• 3

n n n k , D k

     

 

To accurately evaluate these damage parameter we have to accurately know:

• Reactor spectrum, which in turns

depends on reactor materials and geometrical complexity, plus nuclear data

• Damage mechanisms, including

annealing times The challenge for LPRRs, providing largely less damage respect to High Power Research Reactors, is to try to compensate this lack in damage level by a higher accuracy in experimental data.

ASTM standard damage functions The role of low power research reactors (LPPRs)

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The TAPIRO reactor What it means TAPIRO?

TAPIRO (Tapir in English)? Taratura Pila Rapida a potenza zerO Calibration Fast Pile at Zero Power

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The TAPIRO reactor Origins

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The TAPIRO reactor Core layout

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The TAPIRO reactor Experimental channels

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Φ ≈ 3∙1012 n/cm2∙s @ 5 kW Φ ≈ 5∙1011 n/cm2∙s @ 5 kW Φ ≈ 2∙1010 n/cm2∙s @ 5 kW

The TAPIRO reactor Neutronic features

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For a given position k in the reactor and for the i detector all integral experimental techniques measure quantities of the type:

dE ) E ( ) E ( r I

k i E k , i

  

Where ri(E) is the differential-energy response of the i detector and Ii,k is the integral response. TAPIRO neutronic characterization Theoretical basis

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Two broad classes of integral data need to be distinguished: 1. Integral reaction rates where: 1. Equivalent fission fluxes where (in case of fast reactors):

) E ( ) E ( r

i i

 

235 235 235

, i i E i E i i

) E ( dE ) E ( dE ) E ( ) E ( ) E ( ) E ( r

  

       

 

dE ) E ( ) E ( r I

k i E k , i

  

In the second relation denotes a pure 235U fission spectrum.

235





TAPIRO neutronic characterization Theoretical basis

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In the first case we have: In the second case we have:

dE ) E ( ) E ( R I

k i E k , i k , i

   



235 235

, i k , i k , i i E EQ k , i k , i

R dE ) E ( ) E ( I

 

       



TAPIRO neutronic characterization Theoretical basis

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If the observed counting rates from the detectors are given by: And if the efficiencies ε are equal we can write:

dE ) E ( ) E ( N c dE ) E ( ) E ( N c

235 235 235

i E i , i , i k i E i k , i k , i   

       

 

dE ) E ( ) E ( dE ) E ( ) E ( c c

235 235

i E k i E , i k , i  

    

 

Or:

      

    

235 235 235 235

, i k , i E , i k , i EQ k , i

c c dE ) E ( c c

TAPIRO neutronic characterization Theoretical basis

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This is the base concept of “Benchmark-Field Referencing” (inter-laboratories experimental campaign). Reaction rates in TAPIRO have been obtained by:

               

   

235 235 235 235

, i , i k , i EQ k , i , i k , i

c c R

TAPIRO neutronic characterization Benchmark-Field Referencing

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The activity “Flux Maintenance” (at SCK•CEN Mol – Belgium) allowed the certification of the value in cooperation with US NBS (National Bureau of Standards).

2 Cf , i ) R ( Cf , i ) R ( Cf , i , i

R 4 S c c

235 235 235

      

  

NBS (USA)

               

   

235 235 235 235

, i , i k , i EQ k , i , i k , i

c c R

235





TAPIRO neutronic characterization Flux Maintenance

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               

   

235 235 235 235

, i , i k , i EQ k , i , i k , i

c c R

SCK•CEN Mol Cavity 235U Fission Spectrum Standard Neutron Field

TAPIRO neutronic characterization Detectors calibration at SCK•CEN Mol

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               

   

235 235 235 235

, i , i k , i EQ k , i , i k , i

c c R

TAPIRO neutronic characterization TAPIRO measurements

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Benchmark-Field Referencing

    

 

235 235

, i k , i EQ k , i

c c

TAPIRO Flux Maintenance NBS (USA) MOL – BR1 MOL - BR1

TAPIRO neutronic characterization Overall philosophy

IGORR 18 3-7 December 2017, Sydney, Australia

0.00E+00 5.00E+10 1.00E+11 1.50E+11 2.00E+11 2.50E+11 3.00E+11 3.50E+11 4.00E+11

• 45.00
• 35.00
• 25.00
• 15.00
• 5.00

5.00 15.00 25.00 35.00 45.00 ϕ equivalent 1 MeV at 1 kW (n·cm-2·s-1) Radius (cm)

Core Reflector Reflector

32

TAPIRO damage parameters Equivalent 1 MeV neutron flux ) MeV 1 ( F dE ) E , ( ) E ( F ) MeV 1 , (

D n n n D eq

r r    



Diametral channel

IGORR 18 3-7 December 2017, Sydney, Australia

0.00E+00 2.00E+10 4.00E+10 6.00E+10 8.00E+10 1.00E+11 1.20E+11 1.40E+11 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 ϕ equivalent 1 MeV at 1 kW (n·cm-2·s-1) Radius (cm)

Reflector Core

33

TAPIRO damage parameters Equivalent 1 MeV neutron flux ) MeV 1 ( F dE ) E , ( ) E ( F ) MeV 1 , (

D n n n D eq

r r    



Radial 1 channel

IGORR 18 3-7 December 2017, Sydney, Australia

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90

• 45.00
• 35.00
• 25.00
• 15.00
• 5.00

5.00 15.00 25.00 35.00 45.00 Hardness parameter Radius (cm)

Core Reflector Reflector

34 n n eq

dE ) E , ( ) MeV 1 , ( ) ( H r r r   



TAPIRO damage parameters Hardness parameter Diametral channel

IGORR 18 3-7 December 2017, Sydney, Australia

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 Hardness parameter Radius (cm)

Reflector Core

35 n n eq

dE ) E , ( ) MeV 1 , ( ) ( H r r r   



TAPIRO damage parameters Hardness parameter Radial 1 channel

IGORR 18 3-7 December 2017, Sydney, Australia 36

Roundup

• Usually MTRs, having significant powers up to hundreds of MW, are selected as

radiation fields for neutron radiation damage analysis. However when a high quality is needed in terms of knowledge of both intensity and energy spectrum of the neutron field, LPRRs can play their role.

• ENEA TAPIRO fast neutron source reactor has particular features which match

with the above quality requirements, thanks to the neutronic characterization performed following the so-called "Benchmark-Field Referencing” approach.

• TAPIRO damage parameters, in particular 1 MeV equivalent neutron flux and

hardness parameter, show that TAPIRO is well suited for neutronic irradiation damage analyses (at low power).

• Also 1 MW TRIGA RC-1 reactor at ENEA – Casaccia is candidate to perform

neutron irradiations for damage analysis, especially at the core center, and feasibility studies are currently going on.

IGORR 18 3-7 December 2017, Sydney, Australia

Thank you for your attention! mario.carta@enea.it