wir schaffen wissen – heute fÜr morgen
TRANSCRIPT
WIRSCHAFFENWISSEN– HEUTEFÜRMORGEN
Shielding – High Energy Neutrons – Spallation vs. Fission
UweFilges, PaulScherrer InstitutPhilBentley,EuropeanSpallationSource
20th September 2018,
Neutron Energy Classification
Page2
thermal
epithermal
fast
High energy neutrons
<0.15to 0.625eV
> 0.1– 1MeV
Page3
Spallation vs Fission
Spallation
Neutron energy average: 1.2MeVWatt-Fission Spectrum
Neutron energy distribution: depends from proton energy and target !!!
Neutron production – Proton energy
Page4
Goal: Increasing the proton energy
PSI
ESS
Pulsed spallation sources
Page5
ISISTS2– 800MeV proton beam
SNS– 1GeV proton beam
ESS– 2 GeV proton beam
Released Neutron Spectra
Page6
Bigdifference inshielding efforts !!!
Moderation ?
Page7
• Reactor facilities: bigvolumes – basedonhydrogen(heavywater &lightwater)
Goal: slowing downneutrons tothermal energy (notimedependency)
• Spallation sources: efficiently doneonlyinsmallvolumese.g.H2-ModeratorsBeryllium usedas reflector (moderation is50times worseasD2O)
Goal:keeping the timestructure of thereleased neutrons– minimizeabsorption/scattering between targetandsmallmoderator volume
Bigdifference inshielding efforts !!!
Continuous neutron flux
Pulsed neutron flux
Effects on Neutron Scattering Experiments
Page8
How you can shield high energy neutrons ?
Page9
Depends from the Material Cross Sections (Absorption & Scattering)
Goodscattering materials areworkingwell upto1MeV(scattering isdominating)
GEM applications outside high energy physics - Duarte Pinto, Serge Mod.Phys.Lett. A28 (2013)
Fast Neutrons > 10 MeV
Page10
Density of the materials becomes more and more important.
Tungsten – around4-5barn
Hydrogenhascross sections <1barn!!!
Datacanbefoundon: http://www.nndc.bnl.gov/sigma/
Copper – around2-3barn
Resonances !!!
Page11
Ironis nota„good“ shielding material for epithermal neutrons !!!!
High Energy Neutron Shielding
Page12
Shielding Design
Page13
Collimators along the beamline &Layeredstructure(repetition oflayers)ofshielding material
• McStas,aMonteCarloray-tracingcodeforneutronscatteringinstrumentation,simulatesveryefficientevents(neutrons)fromasourcesurfacetothedetectorposition(alternatives:VITESS&Restrax)
SINQ MCNPX-Model
Simulations-Tools• MCNPX (anadvancedMonte-CarloCodeforparticlephysics)isaperfecttoolto
describea3Dneutronsource,includingmoderator&shieldingmaterials …(alternatives:GEANT4&PHITS)
Input:protonbeamorreactorcoremodel
Input:neutron source description
SINQ CATIA-Model SINQ McStas-Model
( )λλ
λ
λλλ λ
λdIdf
iT
iTi
i
i
2
exp241
0
⎟⎟⎠
⎞⎜⎜⎝
⎛−=
=⎟⎟⎠
⎞⎜⎜⎝
⎛∗∗=∑
n- Maxwellian distribution
Examples – PSI & ESS
Page15
ICON– Imaging beamlineHowgoodwecan describe asource?
Eiger– thermal triple axes instrumentNon-magnetic /compact shielding
MAGiC – Single crystal diffractometer
ODIN– TOinvestigations
Zebra– thermal single crystal diffractometer ESTIA– Reflectometer
Cold Source Simulations/Measurements at SINQ
4.7 m7.2 m
11.8 m16.8 m
McStas
MCNPX
no supermirrors are installed, different pinhole geometries are possible,measurement positions are closed to the source with direct view
L.Giller, U.Filges, G.Kuehne, M.Wohlmuther, Nucl. Instr. and Meth. 586 (2008) 59-63
Measurement positions
ICONbeamline
-4 -3 -2 -1 0 1 2 3 4-4
-3
-2
-1
0
1
2
3
4
width [cm]
heig
ht [c
m]
-4 -3 -2 -1 0 1 2 3 4-4
-3
-2
-1
0
1
2
3
4
width [cm]
heig
ht [c
m]
first collimationsection
cold source
9x9 tally grid at collimation entrance
9x9 tally grid 50 cm inside offirst collimation
energy range: 1eV - 0.3 meV (200 bins) – 3000 h computing time
moderator
Simulated Neutron Flux Distribution at the ICON beamport
NEWInputforMcStas
Thermal flux distributionMCNPX results
-20 -15 -10 -5 0 5 10 15 20
0.0
0.2
0.4
0.6
0.8
1.0
Vertical Profile - 20 mm Setup
norm
aliz
ed in
tens
ity
vertical position [cm]
measurement simplified model improved model McStas-MCNPX model
-20 -10 0 10 20-20
-10
0
10
20
-15 -10 -5 0 5 10 15-20
-15
-10
-5
0
5
10
15
20
Comparison of horizontal and vertical beam profils at middle position (11.8m)
using the McStas-MCNPX model - 20 mm aperture
-20 -15 -10 -5 0 5 10 15 200.0
0.2
0.4
0.6
0.8
1.0
Horizontal Profile - 20 mm Setup
norm
aliz
ed in
tens
ity
horizontal position[cm]
measurement simplified model improved model McStas-MCNPX model
measurement
simulation
heig
th
[cm
]he
igth
[c
m]
width [cm]
width [cm]
Neutron flux distribution at ICON middle position
Measurement/simulation of cold source brightness at SINQ
Experiment – TOF setup with collimator system
- chopped : 0.15% duty cycle
- beam size : ø1 mm
- solid angel : 0.693 mStr
peak factor
simulation(detailed) 1.0
measurement(efficiency by MCNP)
1.2
collimator
Detector shielding with sapphire crystal
Cold source
ICON Beamline (MCNP model)
TOF-Setup
NIMAinpreparation
Background measurements with Bonner Sphere Spectrometer
Bonner spheres spectrometer (BSS) Response matrix of the Bonner spheres system
standard Bonner sphere system consists of a He-3 neutron detector and a set of 10 polyethylene spheres
of diameters from 2 to 15 inches (each sphere has a different energy response)
measurementposition
EPFL – Lausanne
Extension of BSS System
Page21
Extended energy range: >2GeV (interesting also for SwissFEL, ESS...)
Shielding Design for the Triple Axes Spectrometer EIGER
Thermal spectrometer EIGER at SINQ
EIGER Monochromator shielding design
water scatterer
MCNPX model
SINQ
target
Primary beamline layout
- Design of anon-magnet shielding with amaximum thickness of 85cm
Page23
• dose rate < 10 µSv/h with a shielding thickness of 85 cm
Calculated gamma and neutron dose rate distribution at the outer surface of monochromatorshielding – 17° position
MCNPX geometry layout for the shielding
calculations – 17° position
• developing/simulations of different compositions of heavy concrete (non-magnetic) with a density of approx. 5.1 g/cm3
• developing a special material composition (tungsten/paraffin) for absorbing (slowing down) fast neutrons
Gamma and Neutron Dose Rates behind the Shielding
Heavy concrete developments
Page24
• 7 different concrete compositions were tested and simulated (all are special PSI compositions)
• non-magnetic / magnetic samples for different applications
• Sample 1: special efforts - stainless steel balls with different sizes and thermal treatment
• In addition Sample 1 includes as mineral Barite – very good gamma shielding material
Comparison: normal concrete: < 0.13 cm-1
Heavy concrete Measurements
Page25
0 100 200 300 400 5001E-3
0.01
0.1
1
10
100
1000
10000
100000
1000000
˚
˚DoseRate˚(!Sv/h)
Thickness˚(mm)
˚E˚Measured˚Data˚B˚Fits˚to˚I0*exp(-bx)
M1(baryte+1.4301)
I0=52200˚˚b=0.313˚cm-1
Incoming spectrum at ICON beamlineAttenuation for the fast Neutrons
Sample with strong steel collimator (1m)
Shielding for background
reduction was needed
12 inch sphere detector
Page26
• design reduces the background by around a factor of 2
triangular spike-surfaces
Optimized neutron trap
neutron trap with flat surfaces
point of
interest
Original neutron trap proposal
Neutron Trap Design for Eiger
- triangular volume is filled with B4Cpowder
- inaddition Eiger uses aSapphire filter for background reduction
Neutron Filter Data for MCNPX/McStas
Page27
Sapphire crystals
within shielding
- Dimension: 26 mm x 26 mm x 10 mm
- Orientation: c-plan
- Precision of orientation: 1 deg
Sapphire filter setup on BOA
A.Freund NIMA 213(1983)495-501
Samples from three different suppliers(Stettler – 4crystals;Korth– 4crystals;Kyburz – 4crystals)
Page28
Sapphire - Neutron Filter Measurements at BOA
fast neutron flux can be reduced by a factor of 12.5 (120 mm sapphire) – Peak Intensity
fast neutrons (1eV - 1 MeV)
cold neutron flux is reduced by 30 –60% (120 mm sapphire)
Comparison MCNPX simulations and Measurements
Resonances ?
Page29
Sapphire - Neutron Filter Measurements at BOA
• Quality of the crystal are comparable between suppliers
• Signal-to-noise can be chosen depending from the application
• Performance of the crystals is relative non-sensitive to the alignment (< 5% within 1 deg)
Application at TRICS/Zebra
Page30
-40 -20 0 20 40-80
-60
-40
-20
0
20
40
60
80after optimisation of TRICS beam path
x [mm]
y [m
m]
-40 -20 0 20 40-80
-60
-40
-20
0
20
40
60
80
x [mm]
y [m
m]
present state at TRICS right after monochromator
NEU
39 cm2
47.5 cm2
(120 cm2)
Monochromator
additional beam reduction
OLD
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-5
0
5
10
15
20
25
30
35
40 sapphire 55 mm sapphire 57 mm sapphire 59 mm sapphire 61 mm
loss
es [p
erce
nt]
wavelength [Å]
intensity loss if Si-Filter (120mm) is replaced by a Sapphire Filter
improved beam reduction
new sapphire filter
Sapphire-Filter vs. Si-Filter
used neutrons
background
- fast neutron background reduced by a factor of 3
(only primary instrument)
- minimal intensity loss for the used thermal neutrons (1.2 & 2.4 Å)
TRICS to Zebra
Page31
Reference model (TRICS)
ZEBRA upgrade modelPoint of Interest
(entrance to secondary beam opening)
n-flux(n/s/cm2/mA)
n-DR(mSv/h/mA)
g-DR(mSv/h/mA)
2.4*105 4.2+/- 0.7 0.55+/- 0.1
A B Cn-flux
(n/s/cm2/mA)
n-DR(mSv/h/mA)
g-DR(mSv/h/mA)
1.25*105 1.39+/- 0.3 0.57+/- 0.2
Dose Rates (DR) are valid for 1500 μA – SINQ power
A – new Sapphire filter
B – new insert for the nitrogen-tank
C – new insert within Monochromator shieldingCollimator: B4C/borated PE/borated Steel
Comparison – Source Spectra
Page32
ESS – April 2016 (bunker report)
neutronspectruminsidecoldmoderator
Comparison SINQ / ESS – Nov. 2013
neutronspectruminfrontofthebeamports
Energy region
0.5 eV – 600 MeV
SINQ ratio: 8:1 (thermal to fast)
ESS ratio: 1:1 (thermal to fast)
ESS ratio: about 1:5 (thermal to fast)
MAGiC Beamline Layout
• polarizedsinglecrystaldiffractometer atbeamport W6
• Cold&thermalbeamextraction
• Ellipticguidesystemwithakinkat80m
Partners: LLB,FZ-Jülich and PSI
0.00E+00
2.00E+06
4.00E+06
6.00E+06
8.00E+06
1.00E+07
1.20E+07
1.40E+07
1.00E-01 1.00E+00 1.00E+01
-2.00E+07
0.00E+00
2.00E+07
4.00E+07
6.00E+07
8.00E+07
1.00E+08
1.20E+08
1.40E+08
1.60E+08
1.00E-09 1.00E-07 1.00E-05 1.00E-03 1.00E-01 1.00E+011.00E+03W6 – beam exit 30 mm x 38 mm
Energy (MeV)
Gamm
a dos
e rate
(muS
v/h)
Total: 27 Sv/h
Energy (MeV)
Neutr
on do
se ra
te (m
uSv/h
)
Total: 447 Sv/h
W6 – beam entrance 30 mm x 124 mm
Incomparison SINQ:around15Sv/h
Neutron and Prompt Gamma Dose Rate at 5.5 m
Neutron flux spectrum
Neutron flux: 8.4*E9 n/s/cm2
0.00E+00
5.00E+04
1.00E+05
1.50E+05
2.00E+05
2.50E+05
3.00E+05
1.00E-01 1.00E+00 1.00E+01
Page35
0.00E+00
2.00E+05
4.00E+05
6.00E+05
8.00E+05
1.00E+06
1.20E+06
1.40E+06
1.60E+06
1.00E-09 1.00E-07 1.00E-05 1.00E-03 1.00E-01 1.00E+01 1.00E+03
W6 – vacuum channel 10 cm x 10 cm (0.5 deg tilt)
Dose rates @ 24.5m
Energy (MeV)
Gamm
a dos
e rate
(muS
v/h)
Total: 0.79 Sv/h
Energy (MeV)
Neutr
on do
se ra
te (m
uSv/h
)Total: 13.8 Sv/h
New SDEF-card defined for guide shielding calculations
Neutron dose rate
Gamma dose rate
Neutron and Prompt Gamma Dose Rate at 24.5 m
High Energy Shutter
Page36
6 drums are positioned within the neutronbunker wall.
Drum Sequence:1. Borax (50% epoxy / 50% B4C)2. Standard steel3. Standard steel4. Borax5. Standard steel6. Tungsten/parafin (density 11.8 g/cm3)Effective thickness: each drum 20 cm
n-dose rate: 15.2 µSv/h
g-dose rate: 0.5 µSv/h (only prompt gammas from the drums)
N-Dose rate can be reduced more by replacing steel with tungsten drums.
Neutronic Background at Sample Position
Page37
F
Shielding around guidebehind 77m:
• 2m heavy concretewith vacuum tube belt
• 75m standard concrete(0.5 m thickness)
Neutron dose rates
E
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E-091.00E-071.00E-051.00E-031.00E-011.00E+011.00E+03
Neutron background at 170 m
@80m ouside guide shielding
tally E: 1.3 µSv/h
@150m inside guide shielding
tally F: 0.2 µSv/h
Fast Neutron flux
4.2 n/s/cm2
T0 – Chopper thickness
TO - Chopper
Page39
Position: @ 6.25 m
Materials:
• Inconel 750
• Tungsten
Thickness:
2 x 15 cm
@ 1 MeV -> reduction factor >100 (Inconel)
@ 1 MeV -> reduction factor >500 (Tungsten)
1.00E+00
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-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04
withoutT0
Inconel750
Tungsten
Energy (MeV)
Neutr
on do
se ra
te (m
uSv/h
)
Neutron dose rate
Prompt pulse
Page40
E2 – Estia beamport
• Reflectometer at beamport E
• Cold neutron beam line
• Elliptic guide system (Selene) – only 40 m long
41
Bunker Components – Detailed Simulations
Re-design of the MCNPX model (includes the geometry from CATIA)
42
Collimator Simulations
43
n - Dose Rates
Det.6
Det.7
Det.8
Det.6 – 40 muSv/h
Det.7 – 85 muSv/h !!
Det. 8 – 0.2 muSv/h
Shielding materials for ESTIA
New high-precision Shielding Material – Mineral Cast
Partner: RAMPF Machine Systems GmbH & Co. KG
Mineral cast is used as the base of high-precision machines EpumentEpustone
Epustone has the mechanical properties of granite – interesting for our ESTIA project
Epument has a high hydrogen content – (composition of quartz, basalt and epoxy)
First test series (14 compositions) on BOA@SINQ (activation, attenuation for diff. E) with BSS system
Optimisation: add a thermal neutron absorber (B4C) in the composition.
Comparison 1 – Standard mineral cast
1
10
100
1000
100 200 300 400 500 600 700 800 900
dos
erat
e [m
uSv/
h]
time [s]
mineralcastgranit
normal concrete
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 20 40 60 80 100 120 140 160
neut
ron
[cou
nts]
material thickness [mm]
mineralcastgranit
heavy concrete
0
5x106
1x107
1.5x107
2x107
2.5x107
3x107
3.5x107
0 20 40 60 80 100 120 140 160
neut
ron
[cou
nts]
material thickness [mm]
mineralcastgranit
normal concrete
Thermal neutron transmission Fast neutron transmission
Activation decay (irradiation time 10 sec)
The tested Granite
includes Thorium!
Mineral cast is better as
standard concrete or granite
12 inch spherebare counter
Comparison 2 – Borated mineral cast – Composition 6
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Thermal neutron transmission Epithermal neutron transmission
Fast neutron transmission
Mineral cast has similar
properties as
heavy concrete !!!
Best samples are: without ash and a high B4C (5%) content -> sample 6 and 9Next Step: increasing hydrogen in sample 6 (was measured in July 2018)
Vacuum tests
03.12.1P Seite48
EPUMENT 130/3 – Gas Treatment
Only for high vacuum environmentmineral cast shows a delayed behaviour, but neutron guides require only 1E-3 mbar
without sample
Page49
Attenuation of Concrete
Neutron Dose rate
Standard concrete: without Boron
Heavy concrete: without Boron, density: 4.4 g/cm3 66 wt% Fe
SINQ Upgrade
Page50
Thank you for your attention.