Stefania Trovati EPFL - CERN
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Transcript of Stefania Trovati EPFL - CERN
S. Trovati - SATIF 10 1
Activation studies for a beta-beam Decay Ring : residual dose rates
during maintenance and airborne activity
Stefania Trovati
EPFL - CERN
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Outline Beta-beams Decay ring Activation studies:
residual dose rates○ collimation section○ arcs
airborne activity
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EURISOL Beta-beams(CERN, IPNO, CEA, GSI, MSL)
Neutrino Source Decay Ring
Ion production ISOL target &
Ion source
Proton Driver SPL
SPS
Acceleration to medium
energy RCS
PS
Acceleration to final energyPS & SPS
Experiment
Ion acceleration
Linac
Beam preparation Pulsed ECR
Ion production Acceleration Neutrino source
,
,
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26He→3
6Li e−ν Average Ecms =1.937 MeV
1018Ne→ 9
18F e+νAverage Ecms =1.86 MeV
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Objectives & Methods Radiological risk assessment for the beta-beam
facility at CERN: full evaluation of all radiation protection aspects of the machines feasibility at CERN.
Problem: no available experimental data for 18Ne and 6He Monte Carlo calculations, carefully…
MC calculations for prompt radiation and induced activity studies: shielding design for tunnels, residual doses and airborne doses.
MC code: FLUKA with BME nucleus-nucleus interactions below 100 MeV/u.
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30o 60o
Comparison study between data and FLUKA with BME
20Ne -> Copper target@ 100 MeV/u Work presented
at:ICRS11 - 2008
(T. NAKAMURA et al., “Measurements of secondary neutrons produced from thick targets bombarded by high
energy Neon ions”, J. Nucl. Sci. Tech., 36, 42 (1999))
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The Decay Ring (DR)
Primary beams: 6He and 18Ne ions at ~92 GeV/u. Decay losses in bumps and arcs (b± decays). Collimation losses in the collimation section. Total number of decays/s in the DR:
€
6He : 6.75E11 (total decayss
)
18Ne : 2.48E11 (total decayss
)
Loss maps: calculated by ACCSIM code. For collimation by ACCSIM+FLUKA.
Same length as
SPS6911.5 m
injection60
2 m
2510 m
Collimation sectionbumps
6He/s: 1.6 E+13 18Ne/s: 2 E+13
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Residual dose rates during maintenance
The beta-beam facility will work for 107 seconds 3 months.
Irradiation cycle: 3 month irradiation followed by 1 hour, 1 day, 1 week waiting times.
The residual H*(10) rate in mSv h-1 scored along the tunnel.
MC calculations: electromagnetic cascade off in prompt radiation, on in decay.
Radionuclide yields estimated.
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Collimation section and bumps
The collimation section stays in between the two bumps and foresees the combination of a primary and two secondary collimators, all made of carbon. In between the collimators and all along the section there are several carbon absorbers.
Collimators
Bump area
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Bump areas: magnet geometry in FLUKA
Magnet layouts from SESAME. Different lengths different massesQuadrupole: 2 m longDipole: 12 m longBeampipe: 8 cm aperture hor., 1.5 cm vert., 1mm thick.
76 cm
45.3 cm
4 cm
20 cm
WARM MAGNETS
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2nd BN3 in the first bump dipole+quadrupole+ long straight section25 m
2nd BN3
BN2 BN2
BN3 BN3Q Q
Q
QQ Q
Q~1010 parts s-1 over 25 m
Q Q
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6HeAfter
1 hourAfter 1 day
After 1 week
The dose rate doesn’t change much between a 1-day and a 1-week waiting
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WORST
CASEDominant residual radionuclides
and their specific activities in the bump magnets
PipeRadionuclide A (Bq g-1)
Cr-51 2.15E+05Mn-56 1.16E+05V-48 9.17E+04
Mn-52 4.91E+04Sc-44 4.62E+04Mn-54 4.05E+04
Sc-44m 2.50E+04Ti-45 2.50E+04Ni-57 1.32E+04Co-56 1.25E+04Na-24 8.13E+03
YokeRadionuclide A (Bq g-1)
Cr-51 7.50E+05V-48 3.11E+05
Mn-52 2.68E+05Mn-54 2.36E+05Mn-56 2.24E+05Fe-55 1.54E+05Sc-44 1.29E+05Ti-45 7.32E+04Co-56 2.87E+04
CoilsRadionuclide A (Bq g-1)
Cu-61 2.71E+05
Co-58 2.05E+05
Cr-51 8.81E+04
Co-57 5.88E+04
Co-61 4.92E+04
Co-56 4.89E+04
V-48 3.68E+04
Mn-52 2.81E+04
Mn-54 2.53E+04
Mn-56 2.19E+04
Ni-65 2.00E+04
Sc-44 1.93E+04
Ni-57 1.78E+04
after 1 hour for 6He
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Summary1h 1d 1w
6He 18Ne 6He 18Ne 6He 18Ne
1st Q- 1st BN2 10 0.72 6 0.36 3.60 0.18
2nd Q 1.51 20 0.61 11 0.45 6
3rd Q - 1st BN3 1.75 1.08 1.05 0.36 0.63 0.27
4th Q 1.50 8 0.60 3 0.45 1.8
2nd BN3 - 7th Q 90 1.81 50 1.08 30 0.54
2nd BN2 - 9th Q 54.41 1.8 30.20 1.08 18 0.54
BN2 BN2
BN3 BN3Q Q
Q
QQ Q
Q
Dump before 2nd BN3 – 7th Qand2nd BN2 – 9th Q
Dumps
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Collimation section: 18Ne
> 100 mSv h-1
•After 1 week the residual dose around the primary collimator is still above the prohibited area limit.
Power deposited in quadrupoles after the primary collimator absorbers required,
decrease of factor 4 on average
Courtesy of E. Bouquerel
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Arcs Arcs are composed of cold magnets, LHC-like. A large aperture allows to avoid losses in the
straight sections (ss) BUT high power deposited in the first dipole in the arcs (10 W/m in ss) dumps.
Worst case study here, with no dumps. Two configurations under study to avoid
magnet quench and high induced activity absorbers between the magnets open mid-plane magnets
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ArcsCase 1: layout for coils in the absorber configuration
•For dipoles: copper wedges implemented separately from cables.•For quadrupoles: compound material that includes copper wedges into cables.•Yoke material composition: 98% iron, 1% nichel, 0.4% manganese, 0.1 % silicon, 0.1% carbonium, 0.2 % copper.
*Courtesy of F. Cerutti ( specifications by J. Miles - N. Mokhov)
*
C. Hoa M. Mauri
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ArcsCase 2: open mid-plane magnets and no absorbers
Aluminum absorbers in the mid-plane
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ARC DIPOLES & QUADRUPOLES
Design by J. Bruer
•Dipole length: 5.687 m•Quadrupole length: 2 m•Absorber length: 1 m•Absorber material: steel
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6He: with absorbers 18Ne: with absorbers
6He: without absorbers 18Ne: without absorbers
Residual dose rates in the arcs with absorbers or with open mid-plane dipoles.
mSv h-1 6He 18Ne
1 hour 1 day 1 week 1 hour 1 day 1 week
With absorbers 0.12-1.2 0.05-0.5 0.015-0.3 0.1-6 0.06-3 0.02-1.5
Open mid-plane dipoles 0.03-1 0.01-0.4 0.001-0.2 0.02-6 0.001-1.2 0.001-0.8
mSv h-1
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Airborne activity Limits for airborne activity: Swiss directive HSK-R-41. 0.2 mSv maximum annual Effective Dose for inhalation. For CERN 10 μSv y-1 for all the installations. 1 μSv y-1 is assumed for each machine in beta-beam
complex. Conversion coefficients Bq->Sv from CERN-SC-2008-
001-IE-TN. Reference population group: 240 m from the stack
(ISOLDE stack). Outdoor and indoor exposures are weighted according
to occupancy factors.
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Methods Air activity:
FLUKA simulations: n, p, p± track length spectrum scoring in the air tunnel. Off-line folding of particle track-length spectra with isotope production cross
sections:
nj = atomic concentration (per cm3) of the element j in the material sijk = cumul. cross section for the nuclide i in the reaction of a particle of type k
and energy E with a nucleus of element j Lk= track length sum of hadrons of type k and energy E
Analytical model for the air diffusion in the tunnel, through the ducts.
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Yi = n j σ ijk (E )Λk (E )dE∫j,k∑
Φ FAsurface
Voll
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Areleased = FAsurface ⋅ l
⋅Y (1− e− l
F⋅Asurfaceλ
)e−Vol
Fλ
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The dominating reaction channels are: Half-life < 1day:
○ 11C (spallation on N and O): 14N(p,a)11C, 14N(p,3H)11C. ○ 13N reactions on nitrogen: (n,2n).○ 14O: (p,n) on nitrogen, neutron removal on oxygen. ○ 15O (reactions with oxygen, especially neutron
removal): (n,2n), (p,2n).○ 41Ar (low-energy neutron capture on argon).
Half-life > 1 day: ○ 7Be (spallation by high energy reactions on N (most)
and O): reactions on Ar play a minor role.○ 38-39-40Cl spallation on argon dominated by neutrons.
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Airborne activity in DR
Radionuclide Half-life Annual dose (mSv)Ar-41 hours 6.94E-03
N-13 minutes 1.26E-03
C-11 minutes 1.60E+00
Be-7 months 3.88E-01
O-15 minutes 9.27E-01
Cl-39 minutes 3.54E-03
Cl-38 minutes 6.16E-02
P-32 days 1.38E-01
Na-24 hours 3.47E-03
O-14 seconds 9.29E-03
6He case.F = 10000 m3 h-1
Tunnel volume = 86852 m3
Exit duct volume = 300 m3
The total annual dose is of 4.5 mSv
ISOLDE conversion coefficients
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Airborne activity in DR
Radionuclide Half-life Annual dose (mSv)Ar-41 hours 1.50E+00
N-13 minutes 1.43E+00
C-11 minutes 1.36E+00
Be-7 months 5.89E-01
O-15 minutes 2.52E-01
Cl-39 minutes 1.86E-01
Cl-38 minutes 8.12E-02
P-32 days 7.71E-02
Na-24 hours 5.63E-02
O-14 seconds 2.07E-02
18Ne case.F = 10000 m3 h-1
Tunnel volume = 86852 m3
Exit duct volume = 300 m3
The total annual dose is of 5.6 mSv
ISOLDE conversion coefficients
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Conclusions Released airborne activity is within Swiss
constraints, but above assumed limits for CERN machines.
Area classification according to CERN: limited stay controlled area to high radiation area, accessible after 1 week or more depending on the position.
Dumps before the arcs are needed. Remote handling during maintenance for the
collimator area. Need for experimental data for comparisons!
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II. Safety code F, classification of areas and personnel
Radiation areas: classification Occupationally exposed workers:Class A > 6 mSv / 12 monthsClass B < 6 mSv / 12 months