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Simulations des niveaux de radiations en arrêt machine M. Brugger, D. Forkel-Wirth, S. Roesler (SC/RP)

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 2 IR7 Radiation Protection Issues Impact on environment activation and release of air activation and release of water activation of rock radioactive waste Impact on personnel (direct) (indirect) remanent dose from radioactive components during interventions stray radiation dose to components (cables, magnets, etc.) production of ozone (corrosion!)

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 3 Detailed model of IR7 (two beamlines incl. dogleg, collimators, dipoles incl. magnetic field, quadrupoles, tunnel, etc.) Layout corresponds to V 6.5 (status March/April 04) Only Phase 1, No Absorbers,… No local shielding (!) Forced inelastic interactions of 7 TeV protons in collimator jaws according to loss distribution obtained from tracking code * Uniform distribution along the jaw, 200 m inside Magnetic field Dogleg fully implemented (incl. field) Magnetic field in the quadrupoles not considered Annual number of protons lost per year at IR7 Environmental calculations (ultimate operation): 7.3 x ** Maintenance calculations (nominal operation): 4.1 x ** FLUKA Simulation Parameters * data provided by R.Assmann ** data provided by M.Lamont (two beams)

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 4 FLUKA-calculations: Geometry IR7 Collimator Dipole Quadrupole Air duct Enclosed sections D4D3Q5Q4 Q5 *Collimators were rotated and positioned in the geometry by using a modified script from Vasilis Vlachoudis

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 5 Design Criterion 2mSv/year/person/intervention

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 6 Calculation Procedure Detailed Geometry description including Correct source terms Loss distributions Complete geometry Tunnel structure Collimator, magnets Beamline, Dogleg separation Monte-Carlo simulation to calculate the remanent dose rates in the entire geometry using the new “Explicit Method” Calculation of dose rate maps for the entire geometry and various cooling times, including Separate simulations for different contributors Average and Maximum Values for relevant locations Compilation of intervention scenarios together with the corresponding groups Time, location and frequency of the intervention Number of people involved Calculation of individual and collective doses Iteration and optimization

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 7 Remanent Dose Rates: Contributions Contributions to total remanent dose rates (180 days of operation, 1 hour of cooling) collimators beampipes TCPTCS D4 D3Q5 Nominal Intensity magnets Tunnel wall and floor

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 8 Remanent Dose Rates: Section between TCP and Q5 Remanent dose rates after 180 days of operation 1 day of cooling 4 months of cooling TCS ~5 mSv/h ~1 mSv/h first secondary collimator (Phase 1) most radioactive component (in the absence of additional absorbers) with over 90% caused by secondary particles from upstream cascades further peaks of remanent dose rate close to upstream faces of magnets dose rate maps allow a detailed calculation of intervention doses Nominal Intensity

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 9 Dose Rate Maps for the Full Geometry Cooling Time of one Day Only Beam 1

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 10 1 hour Dose Rate Maps for the Different Cooling Times 8 hours 1 day1 week 1 month 4 months

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 11 Dose Rate Maps for the Different Cooling Times 1 hour 8 hours 1 day1 week 1 month 4 months

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 12 Chosen Locations for 1 st Estimates Cooling Time of one Day

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 13 Dose Rate Distribution in the Aisle (Pos1) Cooling Time of one Day 2 nd Beam mirrored and added

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 14 Average and Maximum Dose Rates Shows the MAXIMUM intervention time, in order to stay BELOW the design constraint Must NOT BE USED as optimization criterion Even at long cooling times long interventions will become difficult

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 15 Intervention Scenarios - Details To study various maintenance scenarios in order to get a complete view of individual and collective doses at IR7 we need the following information: Kind of intervention Location of the intervention Respective cooling time Number of persons involved Steps of the intervention Time estimate for each step Frequency of the intervention Typical cooling period before intervention In the moment the uncertainty lies in the estimates for the intervention(s), not in the calculation of the remanent dose rates!

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 16 Intervention Scenarios The following scenarios have already been identified and/or studied in more detail. x

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 17 Conclusion Access to the collimation region will strongly depend on the exact location of the intervention as well as the time to be spent there Next to “hot spots” (e.g. collimators, downstream magnets or absorbers) the occupancy time for maintenance operations will be rather short During the first years of operation the situation will be slightly relaxed (factor of ~3) Optimization of intervention scenarios should already begin now in order to be able to adopt last design changes and identify those intervention scenarios important for further improvement

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 18 Backup Slides

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 19 Radiation Protection Legislation: General Principles 1)Justification any exposure of persons to ionizing radiation has to be justified 2) Limitation the individual doses have to be kept below the legal limits 3) Optimisation the individual doses and collective doses have to be kept as low as reasonable achievable (ALARA)

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 20 Radiation Protection Legislation: Optimisation Radiological protection associated with justified activities shall be deemed to be optimized provided the appropriate different possible solutions shall have been individually assessed and compared with each other; the sequence of decisions that led to the particular solution remains traceable; due consideration has been given to the possible occurrence of failures and the elimination of radioactive sources. The principle of optimisation shall be regarded as satisfied for activities which under no circumstances lead to an effective dose of more that 100 Sv per year for occupationally exposed persons or more than 10 Sv per year for persons not occupationally exposed. [Swiss Radiation Protection Legislation (22 June 1994), see also Council Directive 96/29/Euratom ].

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 21 Radiation Protection Legislation: Design Criterion Job dose estimates are legally required in order to optimize the design of the facility and to limit the exposure of personnel CERN design criterion : 2 mSv/year/person

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10 Novembre 2004 Simulations des niveaux de radiations en arrêt machine 22 Dose To Cables Estimate of annual dose distribution assuming a loss rate of 1.1E16 particles per year. (H. Vincke) A change of the cable tray location to the aisle would significantly improve the situation. The plot to the right only includes one beam, thus the real distribution (worst case for the aisle side) would shift more to the left. The expected reduction factor would then go down (from almost 10 as expected in the graph), to ~3-5.

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