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Stefania Trovati EPFL - CERN

Stefania Trovati EPFL - CERN. A ctivation studies for a beta-beam Decay Ring : residual dose rates during maintenance and airborne activity. Outline. Beta-beams Decay ring Activation studies: residual dose rates collimation section arcs airborne activity. EURISOL Beta- beams

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Stefania Trovati EPFL - CERN

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  1. Stefania Trovati EPFL - CERN Activation studiesfor a beta-beam Decay Ring : residual dose rates during maintenance and airborne activity S. Trovati - SATIF 10

  2. Outline • Beta-beams • Decay ring • Activation studies: • residual dose rates • collimation section • arcs • airborne activity S. Trovati - SATIF 10

  3. EURISOL Beta-beams (CERN, IPNO, CEA, GSI, MSL) Ion production Acceleration Neutrino source Experiment Proton Driver SPL Acceleration to final energy PS & SPS Ion production ISOL target & Ion source SPS Neutrino Source Decay Ring Beam preparation Pulsed ECR PS Ion acceleration Linac Acceleration to medium energy RCS S. Trovati - SATIF 10

  4. 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. S. Trovati - SATIF 10

  5. Comparison study between data and FLUKA with BME (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)) 60o 30o 20Ne -> Copper target @ 100 MeV/u Work presented at: ICRS11 - 2008 S. Trovati - SATIF 10

  6. The Decay Ring (DR) bumps Same length as SPS 6911.5 m Collimation section • 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/s: 1.6 E+13 18Ne/s: 2 E+13 602 m injection 2510 m Loss maps: calculated by ACCSIM code. For collimation by ACCSIM+FLUKA. S. Trovati - SATIF 10

  7. Residual dose rates during maintenance • The beta-beam facility will work for 107 seconds  3 months. • Irradiation cycle: 3 month irradiationfollowed 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. S. Trovati - SATIF 10

  8. 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. Bump area Collimators S. Trovati - SATIF 10

  9. Bump areas: magnet geometry in FLUKA WARM MAGNETS Magnet layouts from SESAME. Different lengths  different masses Quadrupole: 2 m long Dipole: 12 m long Beampipe: 8 cm aperture hor., 1.5 cm vert., 1mm thick. 76 cm 4 cm 20 cm 45.3 cm S. Trovati - SATIF 10

  10. 2nd BN3 in the first bump • dipole+quadrupole+ long straight section25 m 2nd BN3 ~1010 parts s-1 over 25 m Q Q BN3 Q Q Q BN3 Q Q Q Q BN2 BN2 S. Trovati - SATIF 10

  11. 6He After 1 hour After 1 day After 1 week The dose rate doesn’t change much between a 1-day and a 1-week waiting S. Trovati - SATIF 10

  12. Dominant residual radionuclidesand their specific activities in the bump magnets worst case after 1 hour for 6He S. Trovati - SATIF 10

  13. Summary BN3 Q Q Q BN3 Q Q Q Q Q Q Dump before 2nd BN3 – 7th Q and 2nd BN2 – 9th Q BN2 BN2 Dumps S. Trovati - SATIF 10

  14. Collimation section: 18Ne > 100 mSv h-1 • After 1 week the residual dose around the primary collimator is still above the prohibited area limit. Courtesy of E. Bouquerel Power deposited in quadrupoles after the primary collimator  absorbers required, decrease of factor 4 on average S. Trovati - SATIF 10

  15. 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 S. Trovati - SATIF 10

  16. ArcsCase 1: layout for coils in the absorber configuration C. Hoa M. Mauri * • 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) S. Trovati - SATIF 10

  17. ArcsCase 2: open mid-plane magnets and no absorbers Aluminum absorbers in the mid-plane S. Trovati - SATIF 10

  18. ARC DIPOLES & Quadrupoles • Dipole length: 5.687 m • Quadrupole length: 2 m • Absorber length: 1 m • Absorber material: steel Design by J. Bruer S. Trovati - SATIF 10

  19. Residual dose rates in the arcs with absorbers or with open mid-plane dipoles. 6He: with absorbers 6He: without absorbers mSv h-1 18Ne: without absorbers 18Ne: with absorbers S. Trovati - SATIF 10

  20. Airborne activity • Limits for airborne activity: Swiss directive HSK-R-41. • 0.2 mSvmaximum 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. S. Trovati - SATIF 10

  21. 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 jin the material • sijk = cumul. cross section for the nuclide iin 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 kand energy E • Analytical model for the air diffusion in the tunnel, through the ducts. Vol F Asurface Φ l S. Trovati - SATIF 10

  22. 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. S. Trovati - SATIF 10

  23. Airborne activity in DR 6He case. F = 10000 m3 h-1 Tunnel volume = 86852 m3 Exit duct volume = 300 m3 ISOLDE conversion coefficients The total annual dose is of 4.5 mSv S. Trovati - SATIF 10

  24. Airborne activity in DR 18Ne case. F = 10000 m3 h-1 Tunnel volume = 86852 m3 Exit duct volume = 300 m3 ISOLDE conversion coefficients The total annual dose is of 5.6 mSv S. Trovati - SATIF 10

  25. 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! S. Trovati - SATIF 10

  26. Radiation areas: classification • Occupationally exposed workers: • Class A > 6 mSv / 12 months • Class B < 6 mSv / 12 months II. Safety code F, classification of areas and personnel S. Trovati - SATIF 10

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