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Activation problems

Activation problems. S.Agosteo (1) , M.Magistris (1,2) , Th.Otto (2) , M.Silari (2) (1) Politecnico di Milano; (2) CERN. Introduction. Problems of material activation: in the target system and its surroundings (for Neutrino Superbeam and BetaBeams)

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Activation problems

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  1. Activation problems S.Agosteo(1), M.Magistris(1,2), Th.Otto(2), M.Silari(2) (1) Politecnico di Milano; (2) CERN

  2. Introduction Problems of material activation: • in the target system and its surroundings (for Neutrino Superbeam and BetaBeams) • in the machines for ion acceleration and in the decay ring (for BetaBeams only) An estimation of the production of residual nuclei in the target station has been performed with FLUKA

  3. 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

  4. MicroShield • A program which analyzes shielding and estimates exposure from gamma radiation • Input: • Dimensions • Material information and build-up factors • Source strength • Integration parameters

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

  6. Target and horns Protonbeam A 2.2 GeV, 4 MW is sent onto the mercury target, inserted in two concentric magnetic horns for pion collection and focusing.

  7. 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)

  8. 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

  9. Activation of mercury Assumptions: • 0.5 m3 of liquid circulating in the system • the mercury is uniformly irradiated • it will circulate in pipes (2 cm radius) and be stored in a spherical tank • 10 years of operation and 1 month cooling

  10. Dose rates due to the mercury Dose equivalent rate at: • 50 cm from a 1 m long pipe, filled with Hg: 320 mSv h-1 • 5 m from the tank, without shielding: 68 mSv h-1 • 10 cm from a droplet (1 mg Hg): 1 Sv h-1

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

  12. Horn, after 6 weeks of irradiation

  13. Dose rates due to the horn • At one metre from the horn, after six weeks of irradiation and one day of decay: Dose equivalent rate: ~10 Sv h-1 • Equipment for the remote handling of the magnetic horns will be mandatory.

  14. Steel pipe • Material: steel P355NH (Fe 96.78%) • 60 m long • Filled with Helium • 10 years of operation • Operational year of 6 months (1.57*107 s/y) Steel pipe

  15. Steel pipe, power density crossing the inner surface

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

  17. Dose rates in the decay tunnel After ten years of operation, one month of cooling • 89% of the dose rate comes from the steel • The dose rate does not depend on the radial position

  18. Earth, after 10 years of operation

  19. Earth, after 10 years of operation

  20. Radioactivity in molasse • There is the risk that the radioactivity in the earth may leach into the ground water. • Radionuclides to be considered: • In a soluble chemical form • With half-lives longer than 10 h 22Na, 3H

  21. Radioactivity in molasse • The radioactivity induced in the rock may leach into the ground water. • Two possible risks: 1) Contamination of surface water (limits on the Bq/year produced) • 2) Contamination of public water supplies (limits on the concentration Bq/l released)

  22. Contamination of public water supplies • Severe constraints for the concentration (Bq l-1) of activity induced in the ground water • The estimation of the concentration of 3H and 22Na requires a hydro-geological study of the construction site • No evaluation can be done, before the site of the facility has been chosen

  23. Contamination of surface water (*) Max dose to the critical group: 0.3 mSv per year, release constraints valid for CERN Meyrinsite only

  24. BetaBeams: induced radioactivity • A large portion of the initial beam will decay during acceleration, and all injected beam is essentially lost in the decay ring • Losses in the decay ring: ~8.9 W m-1 (6He, 139 GeV/u) (*) ~0.6 W m-1 (18Ne, 55 GeV/u) (*) (*) M. Lindroos et al., Neutrino Factory Note 121

  25. BetaBeams: induced radioactivity Lack of data on induced radioactivity from ions • Possible ways of estimating the material activation: • For high-energy particles, an A-nucleus can be approximated by A single protons (It is the easiest way to obtain a first estimation) 2) At GSI, people are working on the implementation of a code, which deals with transport and fragmentation of heavy ions 3) A new version of FLUKA is being implemented

  26. Conclusions • Even if it is not correct to simply scale the induced radioactivity produced in the decay tunnel (~kW/m) to that produced in the decay ring (~W/m), the latter is expected to be much lower than the former. • A good estimation of the induced radioactivity in the decay ring requires a detailed study, possibly using both the simplified model and a Monte Carlo code, if available.

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