Radiation Protection Issues M.Brugger, D.Forkel-Wirth, S.Roesler , H.Vincke SC/RP

1. Radiation Protection Issues M.Brugger, D.Forkel-Wirth, S.Roesler, H.Vincke SC/RP Review of the LHC Collimation Project 30 June – 2 July 2004 Radiation Protection Issues

2. 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!) Radiation Protection Issues

3. Outline 1. Radiation protection legislation 2. Computational methods for the calculation of remanent dose rates 3. Benchmark results for computational methods 4. FLUKA calculations 5. Remanent dose rates between TCP and Q5 6. Intervention dose estimates Radiation Protection Issues

4. Radiation Protection Legislation: General Principles • Justification • any exposure of persons to ionizing radiation has to be justified • 2) Limitation • the personal doses have to be • kept below the legal limits • 3) Optimisation • the personal doses and collective doses have to be kept as low as reasonable achievable (ALARA) Radiation Protection Issues

5. Radiation Protection Legislation: Optimisation • Radiological protection associated with justified activities shall be deemed to be • optimized provided • the appropriatedifferent possible solutionsshall have been individually assessed andcompared with each other; • thesequence of decisionsthat led to the particular solution remainstraceable; • due consideration has been given to thepossible occurrence of failuresand 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 that100mSv per year • for occupationally exposed persons or more than10mSv per yearfor persons • not occupationally exposed. • [Swiss Radiation Protection Legislation (22 June 1994), see also Council Directive 96/29/Euratom ]. Radiation Protection Issues

6. Radiation Protection Legislation: Design Criterion Job dose estimates are legally requiredin order to optimize the design of the facility and to limit the exposure of personnel CERN design criterion :2 mSv/year/person Radiation Protection Issues

7. Computational Methods: Omega-factor Approach • Assumption - contact doserate is proportional to the density of inelastic interactions (stars) • Only valid for - uniformly activated extended block of material - environment where radionuclide production is proportional to the inelastic interaction rate - fixed irradiation and cooling time (typically 30 days and 1 day) - only few materials (e.g., iron, concrete) • Recent improvements(e.g., Rakhno et al., Fermilab-Conf-01/304-E, 2001) - considerslow-energy neutron activation - computed for large number of materials, irradiation and cooling times Dg(Tirr,Tcool) = w(Tirr,Tcool) x rstar Radiation Protection Issues

8. Computational Methods: Explicit Simulation Monte Carlo simulation of particle interactions and transport in beamline and shielding components as well as tunnel/cavern walls with FLUKA • First step: - simulation of isotope productionby high-energy processes, low-energy neutron interactions as well as photonuclear processes - calculation of build-up and decay of radioactive isotopes for arbitrary irradiation pattern and cooling times - storage of information on produced radionuclide in external file • Second step: - sampling of photons, electrons, and positrons from radioactive decay - simulation of electromagnetic cascadeinduced by these particles, e.g., in beamline and shielding components or in air - calculation of remanent dose rates at any point of interest S.Roesler et al., Simulation of Remanent Dose Rates and Benchmark Measurements at the CERN-EU High Energy Reference Field Facility, in Proceedings of the Sixth International Meeting on Nuclear Applications of Accelerator Technology, San Diego CA, U.S.A., 655-662 (2003). Radiation Protection Issues

9. Computational Methods: Benchmark Results (1) Benchmark experiment: • irradiation of samples of different materials in stray radiation field • created by 120 GeV/c beam in copper target • measurement of remanent dose rates with different instruments copper stainless steel iron titanium concrete marble resin boron nitride carbon composites water … p, p+,K+ M.Brugger et al., Benchmark Studies of Induced Radioactivity in LHC Materials, Part I: Specific Activities S.Roesler et al., Benchmark Studies of Induced Radioactivity in LHC Materials, Part II: Remanent Dose Rates to be published in Proceedings of the 10th International Conference on Radiation Shielding ICRS-10, Funchal, Madeira, 9-14 May, 2004 Radiation Protection Issues

10. Computational Methods: Benchmark Results (2) Cooling Times: (1) 22m (2) 31m (3) 59m (4) 1d 6h 28m (5) 17d 10h 39m Radiation Protection Issues

11. Computational Methods: Benchmark Results (3) very good agreement between measured and calculated dose rate (30%) Radiation Protection Issues

12. FLUKA Calculations: Parameters (1) • detailed model of IR7(two beamlines incl. dogleg, collimators, dipoles incl. magnetic field, quadrupoles, tunnel, etc.) • no local shielding (!) • forced inelastic interactions of 7 TeV protons in collimator jaws according to distribution obtained from tracking code * • number of protons lost per beam and year at IR7 (nominal operation): 2.05 x 1016 ** * data provided by R.Assmann ** data provided by M.Lamont Radiation Protection Issues

13. FLUKA Calculations: Geometry of IR7 D4 D3 Q5 Q4 Q4 Q5 Collimator Dipole Quadrupole Radiation Protection Issues

14. FLUKA Calculations: Parameters (2) • calculation of (1) remanent dose rate for section from TCP to Q5 • (2) total number of inelastic interactions (“stars”) in all • collimators (for scaling of results obtained in (1)) • separateFLUKA simulationsfor remanent dose rate from • - collimators, beam pipes • - magnets (dipoles, quadrupoles) • - wall and floor of beam tunnel • 180 days of irradiationand6 different cooling times • - tcool = 1 hour, 8 hours, 1 day, 1 week, 1 month, 4 months • - could be calculated for arbitrary irradiation and cooling times • dose rate includes contributions fromgamma and beta emitter Radiation Protection Issues

15. Remanent Dose Rates: Contributions Contributions to total remanent dose rates(180 days of operation, 1 hour of cooling) TCP TCS D4 D3 Q5 collimators magnets beampipes tunnel wall and floor Radiation Protection Issues

16. 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 ~1 mSv/h ~5 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 Radiation Protection Issues

17. Intervention Doses: Intervention on Vacuum System (1) Intervention scenarios*(collimation system Phase 1) A- Exchange of first secondary collimator due to a leak B- Exchange of first secondary collimator due to a failure C- Dismounting of 2nd beamline Two types of connections • Conflat flanges with bolts • Conflat flanges with chain clamps * scenarios provided by M.Jimenez Radiation Protection Issues

18. Intervention Doses: Intervention on Vacuum System (2) Collimator exchange due to a leak (Conflat flanges with chain clamps) Total accumulated dose per person (vacuum group) in mSv Radiation Protection Issues

19. Intervention Doses: Intervention on Vacuum System (3) Collimator exchange - Summary of different scenarios Total accumulated dose per person (vacuum group) in mSv Reminder: CERN Design criterion - 2 mSv/year/person Radiation Protection Issues

20. Intervention Doses: Intervention on Vacuum System (4) Other collimators:Scaling of results for first secondary collimator (TCS03) to other collimators with the total number of inelastic interactions in the respective collimator Total accumulated dose per person (vacuum group) in mSv Note: The dose might be underestimated if collimator is close to other activated beamline elements (e.g., in case of TCS09, TCS29, TCS31). Radiation Protection Issues

21. Summary • Anew methodto calculate remanent dose rates has been applied to the calculation of intervention doses in the LHC beam cleaning insertions. Only with this method intervention doses can be estimated in this detail. Its accuracy has been estimated in previous benchmark experiments to be within 30%. • Calculations were based on a detailed geometry of IR7 (confirming many results obtained previously with a simplified cylindrical geometry! - not discussed here). • After one day of coolingremanent dose rates close to the most radioactive collimator (Phase 1 of collimation system, no absorbers)are of the order ofseveral mSv/h.At the end of a 4-months shutdown dose rates are expected to be lower by about a factor of five. The calculations did not include local shielding! It would increase intervention doses significantly unless removed remotely before the intervention. • Based on these results thedesign has been optimized, e.g., by quick coupling/ uncoupling systems, etc., and work procedures can be appropriately defined. First intervention dose estimates have been performed and shown compliance with the CERN design goal of 2mSv/year/person after about one week of cooling time depending on the collimator. • Dose rates and accumulated doses are going to beverified by measurementsbefore and • during the first (and any) intervention in the beam cleaning insertions. Radiation Protection Issues