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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.

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Presentation on theme: "1 Activation problems S.Agosteo (1), M.Magistris (1,2), Th.Otto (2), M.Silari (2) (1) Politecnico di Milano; (2) CERN."— Presentation transcript:

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

2 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 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 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 5 The target station 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. Top view

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

7 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 60 m long Inner diameter of 2 m Thickness of 16 mm Cooling system (6 water pipes) Front view

8 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 9 Activation of mercury Assumptions: 0.5 m 3 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 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 cm from a droplet (1 mg Hg): 1  Sv h -1

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

12 12 Horn, after 6 weeks of irradiation

13 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 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*10 7 s/y) Steel pipe

15 15 Steel pipe, power density crossing the inner surface

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

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

18 18 Earth, after 10 years of operation

19 19 Earth, after 10 years of operation

20 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 22 Na, 3 H

21 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 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 3 H and 22 Na requires a hydro-geological study of the construction site No evaluation can be done, before the site of the facility has been chosen

23 23 Contamination of surface water 50 cm thick concrete walls Annual release (Bq per year) Constraint (*) 22 Na 4.6· · cm thick concrete walls Annual release (Bq per year) Constraint (*) 22 Na3.2· · H3H7.8· ·10 15 (*) Max dose to the critical group: 0.3 mSv per year, release constraints valid for CERN Meyrin site only

24 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 ( 6 He, 139 GeV/u) (*) ~0.6 W m -1 ( 18 Ne, 55 GeV/u) (*) (*) M. Lindroos et al., Neutrino Factory Note 121

25 25 BetaBeams: induced radioactivity Lack of data on induced radioactivity from ions Possible ways of estimating the material activation: 1)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 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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