Simulations des niveaux de radiations en arrêt machine

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

Simulations des niveaux de radiations en arrt machine

IR7 Radiation Protection IssuesImpact on environmentactivation and release of airactivation and release of wateractivation of rockradioactive wasteImpact on personnel (direct) (indirect)remanent dose from radioactive components during interventionsstray radiation

dose to components (cables, magnets, etc.)production of ozone (corrosion!)


FLUKA Simulation ParametersDetailed 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 mm insideMagnetic field Dogleg fully implemented (incl. field)Magnetic field in the quadrupoles not consideredAnnual number of protons lost per year at IR7Environmental calculations (ultimate operation): 7.3 x 1016 **Maintenance calculations (nominal operation): 4.1 x 1016 **

* data provided by R.Assmann** data provided by M.Lamont (two beams)


FLUKA-calculations: Geometry IR7CollimatorDipoleQuadrupoleAir ductEnclosed sectionsD4D3Q5Q4Q4Q5*Collimators were rotated and positioned in the geometry by using a modified script from Vasilis Vlachoudis


Design Criterion 2mSv/year/person/intervention


Calculation ProcedureDetailed Geometry description includingCorrect source termsLoss distributions Complete geometryTunnel structureCollimator, magnetsBeamline, Dogleg separationMonte-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, includingSeparate simulations for different contributorsAverage and Maximum Values for relevant locationsCompilation of intervention scenarios together with the corresponding groupsTime, location and frequency of the interventionNumber of people involvedCalculation of individual and collective dosesIteration and optimization


Remanent Dose Rates: ContributionsContributions to total remanent dose rates (180 days of operation, 1 hour of cooling) collimators beampipesTCPTCSD4D3Q5Nominal IntensitymagnetsTunnel wall and floor


Remanent Dose Rates: Section between TCP and Q5Remanent dose rates after 180 days of operation1 day of cooling 4 months of coolingTCS~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 dosesNominal Intensity


Dose Rate Maps for the Full GeometryCooling Time of one DayOnly Beam 1


Dose Rate Maps for the Different Cooling Times1 hour8 hours1 day1 week1 month4 months


Chosen Locations for 1st EstimatesCooling Time of one Day


Dose Rate Distribution in the Aisle (Pos1)Cooling Time of one Day2nd Beam mirrored and added


Average and Maximum Dose RatesShows 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


Intervention Scenarios - DetailsTo 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 interventionLocation of the interventionRespective cooling timeNumber of persons involvedSteps of the interventionTime estimate for each stepFrequency of the interventionTypical 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!


Intervention ScenariosThe following scenarios have already been identified and/or studied in more detail. x


ConclusionAccess 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


Backup Slides


Radiation Protection Legislation: General PrinciplesJustificationany exposure of persons to ionizing radiation has to be justified

2) Limitationthe individual doses have to be kept below the legal limits

3) Optimisationthe individual doses and collective doses have to be kept as low as reasonable achievable (ALARA)


Limits per 12-months period (mSv)

Public

Exposed Workers

B

A

EURATOM

< 1

< 6

< 20

France

< 1

< 6

< 20

CERN

< 0.3

< 6

< 20

Switzerland

< 1

< 20

Radiation Protection Legislation: OptimisationRadiological 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 100mSv per year for occupationally exposed persons or more than 10mSv per year for persons not occupationally exposed. [Swiss Radiation Protection Legislation (22 June 1994), see also Council Directive 96/29/Euratom ].


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


Dose To CablesEstimate 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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Simulations des niveaux de radiations en arrêt machine