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


Outline Beta-beams Decay ring Activation studies:

residual dose rates○ collimation section○ arcs

airborne activity


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

,

,

€

26He→3

6Li e−ν Average Ecms =1.937 MeV

1018Ne→ 9

18F e+νAverage Ecms =1.86 MeV


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.


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))


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


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.


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


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


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


6HeAfter

1 hourAfter 1 day

After 1 week

The dose rate doesn’t change much between a 1-day and a 1-week waiting


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


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

QQ

Dump before 2nd BN3 – 7th Qand2nd BN2 – 9th Q

Dumps


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


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


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


ArcsCase 2: open mid-plane magnets and no absorbers

Aluminum absorbers in the mid-plane


ARC DIPOLES & QUADRUPOLES

Design by J. Bruer

•Dipole length: 5.687 m•Quadrupole length: 2 m•Absorber length: 1 m•Absorber material: steel


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


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.


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.

€

Yi = n j σ ijk (E )Λk (E )dE∫j,k∑

Φ FAsurface

Voll

€

Areleased = FAsurface ⋅ l

⋅Y (1− e− l

F⋅Asurfaceλ

)e−Vol

Fλ


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.


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


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


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



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


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!


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

stefania trovati epfl - cern

Documents

residual h

residual doses

decay losses

betabeam decay ring

collimation losses

bumpsthe collimation

accsim fluka

prompt radiation