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KEK Radiation Related Topics

KEK Radiation Related Topics. Yuichi Oyama (KEK). for. neutrino beam construction subgroup. and. target monitor subgroup. Nov-11-2003@NBI2003. Contents. (1) Proton beamline. (2) Target Station. beam period. after beam stop. maintenance. (3) Decay Volume. (4) Beam dump / Muon pit.

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KEK Radiation Related Topics

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  1. KEK Radiation Related Topics Yuichi Oyama (KEK) for neutrino beam construction subgroup and target monitor subgroup Nov-11-2003@NBI2003

  2. Contents (1) Proton beamline (2) Target Station • beam period • after beam stop • maintenance (3) Decay Volume (4) Beam dump / Muon pit (5) Cooling water (6) Air/Helium

  3. Radiations in the Proton Beamline Following energy loss are assumed from our experience. ● Arc Section Preparation Section 0.75kW point loss 1W/m line loss H < 5mSv/h (line loss) and Regulations ● H < 11mSv/h (point loss) at boundary of the concrete H < 0.25mSv/h at surface of the Soil Soil Final Focusing 0.25kW point loss Concrete

  4. Example : Shielding around the tunnel The thickness of the shielding is calculated by the Moyer’s formula and MARS simulation. ● 1.2mSv/h 0.25mSv/h 6.2m soil 11mSv/h 5.6m soil 2.5m concrete 0.05mSv/h 2.3m concrete 5.0m air 2.5m air Arc section Final Focusing section

  5. Example : Radiation in the Access Tunnel For more complicated geometry, MARS simulation is employed. ● H～0.5mSv/h The graphical view of the calculation shows that the ‘kink’ of the access tunnel effectively reduce the radiation. ●

  6. Schematic view of the Target Station ２２ｍ ３３ｍ Surface building 40tonne crane １１ｍ ground level Concrete Concrete service pit Beam Window Final Focusing section Iron Shielding Underground machine room Decay Volume Helium Container storage of radioactive materials Beam Window Concrete Iron Shielding Buffle Target, 1st Horn 2nd Horn 3rd Horn

  7. Radiation during the beam operation Three Regulations must be satisfied. 20cm Concrete wall fence H < 12.5mSv/h@floor of surface building （１） （３） H < 0.25mSv/h@out of the control area Concrete 4.5m Conc 1m Iron2.2m Iron1.5m （２） H < 5mSv/h@boundary of the concrete Iron1.5m Concrete 3.6m

  8. Calculation of shielding thickness by MARS Instead of 3D real geometry, virtual cylindrical geometry is used to improve statistics. ● ● Calculation with 3D real geometry are in progress for the final confirmation.

  9. Example: floor of the surface building Target station r z With 4.5m of concrete above the service pit, radiation at floor of the surface building satisfy H<12.5mSv/h

  10. Determination of the control area boundary by MCNP Neutron sources are defined on the floor, and the dose above the floor is adjusted to be 12.5mSv/h. ● Surface building Top view 12.5mSv/h 0.25mSv/h We need 10m between the surface building and the fence ●

  11. Radiation Control Area 低温設備 Target Station Control area (class-1) 2nd machine room Control area (class-1) Control area (class-2)

  12. Residual Dose after beam stop After beam stop and ventilation, we must access this area Machine room Service Pit After 1 year operation and 1 day cooling with 0.75MW, the residual dose at the top of the iron shielding is ~0.1 mSv/h We can enter and work in the service pit.

  13. Exchange of the target and/or horn Open the top of the beamline shielding ● Broken target/horn is highly radioactivated, and must be kept in the storage of radioactive materials for several years. ● The shielding also must be kept in the storage during the exchange ● Target station : Cross-sectional view Target station : top view storage of radioactive materials

  14. Residual dose of the Target/Horn Residual dose of 3cmF x 90cm Carbon Graphite target (in a Al container) and 1st magnetic horn is calculated. ● 50GeV 0.75MW proton After 1 year operation (1)NMTC/JAM(nmtclib95) + DCHAIN-SP + QAD-CGGP2 (2)Hadron fluence(MARS) + cross section(9mb) + 7Be life Horn must be kept in the storage for more than 10 years. ●

  15. 0.1mSv/h Concrete 1m 22mSv/h 0.56Sv/h Iron 2.2m 0.65Sv/h Aluminum 0.2m Residual dose of the Shielding ● Residual dose of the shielding calculated by MARS (1 year operation, 1 day cooling, 0.75MW) Use of Al surface reduce the radiation about one order of magnitude. ● Further calculation is needed after the “scenario” is fixed. ●

  16. Open the shielding 3m Requirement for the boundary during the maintenance MCNP is used. g-ray source are ● defined on the Al tunnel surface. 0.75MW 1-year operation, 1-day cooling 0.25mSv/h 0.4Sv/h Radiation from residual dose in the tunnel is satisfactory small. ●

  17. 30-40 m downstream of target station 5mSv/h log(H(mSv/particle)) 5.5m He Concrete Concrete thickness (m) Calculation ofDecay VolumeShielding As the target station, virtual cylindrical geometry is used in the MARS calculation. ● 5.0～5.9m of concrete and additional ～6m of soil are needed to satisfy concrete and soil surface condition ●

  18. Radiation behind the Beam Dump At the muon pit, muons from p→nm must be measured with energy threshold of 2～5GeV to study neutrino property. ● Copper 1.5m + Iron 1.5m + concrete 0.5m satisfy this requirement. The threshold for the muons is Eth～4.5GeV ● The residual dose in the muon pit(30days beam, 1 day cooling, 0.75MW) is 0.2mSv/h. ● ● We can enter the muon pit after the beam stop.

  19. To 2nd machine building Management of Cooling Water ● Regulation : Radioactive water can be exhausted to outside (ocean) if radioactivity is less than 15Bq/cc. Radioactive primary cooling water is circulated only in the underground control area during the beam period. ● Target/Horn cooling Heat exchange Primary cooling water system Secondary cooling water system Third cooling water system

  20. TS underground machine room Beam Dump machine room Decay Volume Heat exchange Heat exchange Disposal Scenario of Radioactive Water ● After 20days operation, the all radioactive water is transferred to a DP tank in the disposal system. The cooling system for the decay volume is used for this purpose (to save money). They are mixed with fresh water in the dilution tank. ● Primary cooling water from Target/Horn Primary cooling water from Beam Dump DP tank Fresh water After measurement of radioactivity in the dilution tank, the water can be disposed. It takes 1 or 2 days for the measurement. ● Dilution tank Disposal line

  21. Summary of cooling water and their radio-activation 0.75MW , 20days operation ● We need a capacity of ～600m3 to dispose all together. If we make 60m3 dilution tank, we must repeat the dilutions 10 times. We must also consider a possibility to confine the primary cooling water in the radiation control area forever. ●

  22. Ventilation of Air and Helium Regulation : Radioactive gas (air/Helium) can be ventilated to environment if radioactivity is less than 5mBq/cc. ● Air in the low radioactivity area (e.g. surface building) is always ventilated even during the beam period. ● High radioactivity area (e.g. underground control area) is closed in the beam period. ● After the beam stop, high radioactive air/Helium must be mixed with fresh air and ventilated gradually if the radioactivity exceed 5mBq/cc.

  23. Summary of Air/Helium and their radio-activation 0.75MW , 20days operation sair=30mb, sHe=1.2mb, Ventilation : 8000m3/h, < 5mBq/cc A : Ventilate during beam period; B : Ventilate directly after beam stop C : Ventilate by mixing with fresh air after beam stop

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