Radiation Protection at the LHC Lessons Learned D. Forkel-Wirth, D. - - PowerPoint PPT Presentation

Radiation Protection at the LHC Lessons Learned

• D. Forkel-Wirth, D. Perrin, S. Roesler, C. Theis,

Heinz Vincke, Helmut Vincke, J. Vollaire CERN-SC-RP-SL

13 October 2006, ILC and LHC Forum

Lessons learnt about

RP involvement into a project Choice of RP design parameters Code development and benchmarking Implementation of ALARA Radiation monitoring system Radioactive waste management

RP resources for LHC

• LHC machine:

1 - 2 senior RP physicists FTE x 12 years 1 - 2 Fellows x 12 years

• LHC experiments:

RP “observer status”: providing guide lines RP link person (since 2003) By far not all lay-outs, lay-out modifications and their impact on the radiation levels can be followed up - nevertheless a lot was achieved

RP resources for LHC

Conclusion:

• Savings in RP man-power during the project phase will cause additional

costs during the construction phase

• by last minute changes

during operation

• by increased waiting times,
• limitation of access
• technical modifications
• higher personal and collective doses
• RP has to be closely involved into the project (machine and experiment)

and to be treated like all other sub-project groups with respect to staffing and budgeting – from the design phase onwards

RP Design Parameters for LHC

Dose rate constraints for areas accessible during beam operation

Total beam loss “Normal” beam loss Ambient Dose Equivalent in mSv Ambient Dose Equivalent Rate in uSv/h Simple Controlled Area 50 10 Supervised Area 2.5 1 Non-designated Area 0.3 0.1

Fortunately very conservative parameters were chosen in 1995 but still problems in 2006: Consequence: in some cases we had to abandon all safety margins with respect to calculations (a safety factor of two to three is normally applied)

1 mSv 2.5 mSv 20 mSv 50 mSv 3 uSv/h 10 uSv/h 2006 1995 Internal exposure of the public: < 10 uSv per year to the critical group (> 2003)

RP Design Parameters

• Difficult task to define design parameters for dose rates and

dose for projects whose design and operation stretches over decades as the development of RP legislation over these decades must be anticipated

• Apply very conservative RP parameters and “pessimistic”

beam parameters (e.g. ultimate beam intensity for environmental impact).

• In the worst case: adjust your parameters – it will pay off on

long term

Code development and benchmarking

Required by the Swiss and French Authorities:

• Estimate of collective and personal dose during maintenance
• f the LHC
• Characterization of the future radioactive waste (nuclide

vector)

• > Development and benchmarking of the Monte Carlo code was

required

Personal and collective dose during maintenance

Consignes à appliquer lors des activités de maintenance en fonction des débits de doses ambiants. Niveau de référence du débit de doses ambiant Consignes à appliquer lors des activités de maintenance > 100 µSv/h Tous les travaux doivent être soigneusement planifiés et optimisés. > 2 mSv/h Tous les travaux doivent être soigneusement planifiés ; la durée de l’intervention dans la zone doit être strictement limitée ; la télémanipulation des composants est à envisager sérieusement. > 20 mSv/h Aucun travail n’est autorisé dans les endroits où les débits de doses sont supérieurs à cette valeur, car les limites de dose seraient trop facilement atteintes voir dépassées. La télémanipulation des objets est essentielle.

< 2003: Monte Carlo codes could not provide three dimensional dose rate

maps – only dose rates on “infinite” surfaces were available -> dose estimates would have resulted in unrealistic high numbers

Personal and collective dose during maintenance

• 2003: FLUKA code development enables realistic, three

dimensional dose rate maps:

• detailed calculation of radioactive isotopes produced by

spallation reaction in the various materials

• transport of decay product (β, γ) through matter
• > realistic dose rates become available in three dimensions
• > maintenance scenario * dose rates = personal dose!

Benchmarking at CERN- High-Energy Reference Field (CERF) facility

Location of Samples: Behind a 50 cm long, 7 cm diameter copper target, centered with the beam axis

Benchmarks - CERF

• Different materials typical for

the LHC

• Measurments and simulations

for a large number of cooling times

• Very good agreement was

found between the simulation and the experiment (disagreements less than 20 %)

SPS-LHC Injection Test

121.6 cm

12.0 cm 26.0 cm

Graphite Cu (reduced density) Steel 8.0 cm 9.2 cm 8.2 cm

• Full scale collimator test in

the SPS-LHC transfer line (TT40)

• Dose rates were measured

at two different cooling times of one week and one month

• Very good agreement

within 10%

• Confirmed the accuracy
• f the new simulation

approach

* H. * H. Vincke Vincke

Results TT40

• 20
• 10

• 20
• 10

• 20
• 10

• 20
• 10

1st Measurement after two weeks of cooling Measured dose rate: 0.95 mSv/h Simulated dose rate: ~1.1 mSv/h 2nd Measurement after one month of cooling Measured dose rate: 0.4 mSv/h Simulated dose rate: ~0.4 mSv/h

* H. * H. Vincke Vincke

ALARA: Collimator Exchange LHC Point 7

ALARA

• Use of plug-in system for collimators allowing short installation and replacement times.
• Orientation of accelerator components in order to facilitate the access to the connection boxes

at their less-radioactive end.

• Flanges for vacuum pipes which allow for easy coupling/de-coupling.
• Remote bake-out system for critical parts.
• Patch-panels for cables allowing an easier replacement and the use of especially radiation-

resistant cables in high-loss areas.

• Use of cables with a radiation resistance of at least 500kGy.
• Placement of ionization chambers (PMI) to monitor remotely residual dose rates at locations

with the highest expected losses.

• and….

Radiation Monitoring System

• Radiological survey of work places:
• Measurement of ambient dose equivalent H*(10) [Sv] in pulsed, high energy,

mixed radiation fields

• Challenge:
• Correct
• Reliable
• State-of-the-art
• Compliant with international standards and legal requirements
• Radiation Monitoring System for the Environment and Safety for LHC

(RAMSES):

• utsourced to a company
• strong technical collaboration with CERN

RAMSES

with location ID Radiation Display Display Control box Radiation Monitor

Monitor

Controller Direct hardware connection Tap box

Basic Area Controller

with ID + local database RP Data Base long term storage RP User Interface Remote User Interface

Internet LHC point (local Network) CERN Networks (Ethernet)

RP User Interface Configuration and Supervision Manager

~ 400 detectors of various types ~ 6 Mill. CHF 5.5 FTE (CERN)

1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01

Energy [GeV] d Φ / d ln(E) [1/cm2]

kaons pion+ pion- neutrons protons photons electrons 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01

Energy [GeV] d Φ / d ln(E) [1/cm2]

kaons pion+ pion- neutrons protons photons

inside the tunnel behind shielding

Particle fields

Air filled ionisation chamber (PMI) wall: C-H2 volume: 3 l gas: air, 1 atm voltage: 400 V High-pressure ionisation chamber (IG5) volume: 5,2 l active gas: Ar or H (20 bar) high-voltage: 1200 V

Comparison of Experiment and Simulations

SPS secondary hadron beam is hitting a copper target irradiation of the PMI chambers with different radiation fields at various positions.

Pos 1 Pos 2 Pos 3 Pos 4 Pos 5 Pos 6

Hadron beam

Cu target Beam parameters:

• Momentum:

120 GeV/c

• Intensity:

9*107 hadrons/ SPS cycle (16.8 s with 4.8 s continuous beam)

• Composition:

60.7% π+ 34.8% p 4.5% K+

Set-up in the CERF Target Area

air filled plastic chambers

1E-4 1E-3 0.01 0.1 1 10 100 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1

Position 2

neutrons photons

• ch. hadrons

e

+/e

• dΦ/dln(E)

Energy (GeV)

Pos 6 Pos 5 Pos 4 Pos 3 Pos 2 Pos 1 beam

Simulation of Particle Fluences

Pos 6 Pos 5 Pos 4 Pos 3 Pos 2 Pos 1 beam

1E-4 1E-3 0.01 0.1 1 10 100 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1

Position 4

neutrons photons

• ch. hadrons

e

+/e

• dΦ/dln(E)

Energy (GeV)

Simulation of Particle Fluences

1E-4 1E-3 0.01 0.1 1 10 100 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1

Position 6

neutrons photons

• ch. hadrons

e

+/e

• dΦ/dln(E)

Energy (GeV)

Pos 6 Pos 5 Pos 4 Pos 3 Pos 2 Pos 1 beam

Simulation of Particle Fluences

± 0.146 0.936

± 17,99 115,74 ± 0,82 108,31

Pos 6 ± 0.115 1.076

± 9,47 89,39 ± 1,26 96,20

Pos 5 ± 0.119 1.080

± 8,67 79,00 ± 0,64 85,33

Pos 4 ± 0.104 1.003

± 6,93 67,25 ± 0,73 67,46

Pos 3 ± 0.107 1.031

± 1,56 15,58 ± 0,44 16,06

Pos 2 ± 0.102 0.998

± 0,56 5,64 ± 0,12 5,63

Pos 1 Error Simulation/ Measurement Measurement error *10-6 Measurement Counts/

• prim. part. *10-6

Simulation error *10-6 Simulation Counts/

• prim. part.

*10-6

Comparison of simulation and experiment

PS super-cycle

1 4 .4 s

BOOSTER

1 .2 s SPS

FI X TARGETS North & W est areas

East area AD East area SPP SPN SPS ( Machine Developm ent)

Time resolution

• f monitoring:

0.2 s + x * 0.1 s

RAMSES

LHC in future 0.9 s or 0.6 s

Read-Out Electronics

I ntegrator Comparator Threshold Control circuitry Charge pump I nput (charge) charge buffer Output signal (frequency) Integrator Input (charge) Output signal (fieldbus) Processor Low charge injection switch Adaptive digitizer

For pulsed fields the read-out electronics has to be based on charge digitizers Range to be covered: 10-14 A (background level) - 10-5 A Switching not permitted! Present CERN electronics covers 5 – 6 decades Newly developed: 9 – 10 decades First tests: electronics measures reliably up to 300 nC/pulse ~ 50 mGy/hour (LHC injection)

Conclusion

• Outsourcing possible
• Strong technical involvement of CERN-RP required
• Resources are limited - but nevertheless:

RAMSES: state of the art monitoring system

Radioactive waste management

• Reduce radioactive waste already in the design phase – keep

amount of material inside the tunnel and the experimental cave ALARA

• Disposal of radioactive waste is expensive

France: ~ 3 kEuro/m3 Switzerland: ~ 30 kCHF/m3

• Conditioning center required (CERN: ~ 7 FTE)
• Interim storage space needed

More ….

• Workshops for radioactive material (try to group them)
• State of the art operational dosimetres
• Adequate RP training of workers
• RP involvement comprises more than just RP issues (e.g.

damage to material, High Level Dosimetry)

Conclusions

• Don’t forget about RP resources and close RP involvement

already in the design phase

• Pool of Monte Carlo specialists required - allows cost-

efficient design

• Monte Carlo Code development might be required
• Use very conservative RP design parameters
• Radiation monitoring system needs to be designed
• Radioactive workshops required
• Radioactive waste to be minimised