Activation problems

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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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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

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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

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MicroShield

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

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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.

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Target and horns
Proton beam

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

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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)
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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

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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

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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

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Horn

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

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Horn, after 6 weeks of irradiation
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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.

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Steel pipe

• Material steel P355NH (Fe 96.78)
• 60 m long
• Filled with Helium
• 10 years of operation
• Operational year of 6 months (1.57107 s/y)

Steel pipe
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Steel pipe, power density crossing the inner
surface
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Steel pipe, after 10 years of operation
1 year of cooling
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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

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Earth, after 10 years of operation
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Earth, after 10 years of operation
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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

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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)

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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

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Contamination of surface water
50 cm thick concrete walls Annual release (Bq per year) Constraint ()
22Na 4.61012 4.21011
260 cm thick concrete walls Annual release (Bq per year) Constraint ()
22Na 3.21010 4.21011
3H 7.81011 3.11015
() Max dose to the critical group 0.3 mSv per
year, release constraints valid for CERN Meyrin
site only
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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

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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

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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.