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Induced radioactivity in the target station and in the decay tunnel from a 4 MW proton beam

Induced radioactivity in the target station and in the decay tunnel from a 4 MW proton beam. S.Agosteo (1) , M.Magistris (1,2) , Th.Otto (2) , M.Silari (2) (1) Politecnico di Milano; (2) CERN. Introduction. In a Neutrino Factory, neutrinos result from the decay of high-energy muons

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Induced radioactivity in the target station and in the decay tunnel from a 4 MW proton beam

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  1. Induced radioactivity in the target station and in the decay tunnel from a 4 MW proton beam S.Agosteo(1), M.Magistris(1,2), Th.Otto(2), M.Silari(2) (1) Politecnico di Milano; (2) CERN

  2. Introduction • In a Neutrino Factory, neutrinos result from the decay of high-energy muons • These muons are themselves decay product of a pion beam generated by the interaction of a high-intensity proton beam with a suitable target

  3. Introduction There are two different ideas for producing a neutrino beam: • Muon storage ring • Neutrino super beam These results give some guide-lines, which are intended for both facilities

  4. Introduction • An important aspect of a future Neutrino Factory is the material activation in the target system and its surroundings. • A first estimation of the production of residual nuclei has been performed by the Monte Carlo cascade code FLUKA

  5. FLUKA simulations • A compromise between CPU time and precision: A simplified geometry DEFAULTS SHIELDIN, conceived for calculations for proton accelerators The new evaporation module is activated (EVAPORAT) The pure EM cascade has been disabled

  6. An overview of the facility Top view Top view The facility consists of a target, two horns, a decay tunnel and a dump. It is shielded by 50 cm thick walls of concrete and is embedded in the rock.

  7. Target and horns Protonbeam • A 4 MW, 2.2 GeV proton beam is sent onto the target with a flux of 1.1E16 protons/s. • A liquid mercury target is presently being considered, inserted in two concentric magnetic horns for pion collection and focusing.

  8. Decay tunnel The decay tunnel consists of a steel pipe filled with He (1 atm), embedded in a 50 cm thick layer of concrete Front view 60 m long Inner diameter of 2 m Thickness of 16 mm Cooling system (6 water pipes)

  9. Rooms for maintenance • Two small rooms of 6 m2, filled with air, have been placed upstream of the magnetic horns for dose scoring • Two concentric magnetic horns • (300 kA, 600 kA) surround the target Top view

  10. Rooms for maintenance • Two small rooms of 6 m2, filled with air, have been placed upstream of the magnetic horns for dose scoring • Two concentric magnetic horns • (300 kA, 600 kA) surround the target Side view

  11. Beam dump Downstream of the decay tunnel, a dump consisting of: • An inner cylinder of graphitic carbon • An outer cylinder of polycristalline graphite • An iron shielding Side view

  12. Surroundings • The whole structure (target, horn and decay tunnel) is embedded in the rock, which has been divided into 100 regions for scoring the inelastic interaction distribution

  13. Surroundings • The whole structure (target, horn and decay tunnel) is embedded in the rock, which has been divided into 100 regions for scoring the inelastic interaction distribution

  14. Horn • Material: ANTICORODAL 110 alloy (Al 96.1%) • Irradiation time: six weeks • Specific activity (Bq/g) at different cooling times

  15. Horn, after 6 weeks of irradiation

  16. Steel pipe • Material: steel P355NH (Fe 96.78%) • Average values for the whole pipe (60 m long) • 10 years of operation • Operational year of 6 months (1.57*107 s/y) • Specific activity (Bq/g) Steel pipe

  17. Steel pipe, after 10 years of operation

  18. Steel pipe: 24 regions for scoring • In order to obtain the spatial distribution of stars and induced radioactivity, the steel pipe has been divided into 24 regions 1.6 cm thick 5 m long

  19. Steel pipe, star density per proton

  20. Steel pipe, after 10 years of operation 1 year of cooling

  21. Steel pipe, power density crossing the inner surface

  22. Steel pipe, central part • Induced activity (Bq/g) in the central part of the pipe and multiples of EL (Exemption Limits) calculated with the addition rule

  23. Steel pipe, after 10 years of operation

  24. Steel pipe, after 10 years of operation

  25. Concrete • The target system is shielded by 50 cm thick walls of concrete • Specific activity (Bq/g) after 10 years of operation, operational year of 6 months Concrete around the tunnel Air He Concrete around the horn

  26. Concrete, after 10 years of operation

  27. Earth around the decay tunnel The distribution of the induced radioactivity in the earth has been obtained: • Dividing the earth into six concentric layers (1 m thick)

  28. Earth around the decay tunnel The distribution of the induced radioactivity in the earth has been obtained: • Dividing each layer into twelve regions

  29. Earth, after 10 years of operation

  30. Earth, after 10 years of operation

  31. Earth, after 10 years of operation

  32. Earth, after 10 years of operation 1 year of cooling Exponential fit at 10 m,35 m,55 m from the target. Lambda=0.86 (+/-2.2%)

  33. Earth, after 10 years of operation

  34. Earth, after 10 years of operation

  35. Conclusions • Every year of operation, 4 horns become highly radioactive and require a long term deposit, e.g. underground close to the facility • After 10 years of operation, the steel pipe in the decay tunnel, the concrete and a 2 m thick layer of earth have to be treated as radioactive waste • Outside this “hot region”, after 10 years of operation and 20 years of cooling the induced radioactivity in the earth goes below the Swiss exemption limit

  36. Future work Based on these simulations, estimation of the dose-equivalent rate due to • The horn • The steel pipe • The concrete for maintenance, dismantling and radiation-protection issues

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