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CNGS operation and environmental issues

CNGS operation and environmental issues. F. Malacrida, T. Schmittler, P . Vojtyla, H. Vincke. Outline . Environmental issues Tritium issue and mitigation Dose to public due to water and air releases from CNGS Operational (radiation protection) issues Exchange of two vacuum Be windows

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CNGS operation and environmental issues

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  1. CNGS operation and environmental issues F. Malacrida, T. Schmittler, P. Vojtyla,H. Vincke

  2. Outline • Environmental issues • Tritium issue and mitigation • Dose to public due to water and air releases from CNGS • Operational (radiation protection) issues • Exchange of two vacuum Be windows • Traceability system for radioactive equipment at CERN

  3. Tritium level in CNGS sumps TNM42: • H-3 activity : ~370 Bq/l, almost dry, water inflow negligible TNM41: • H-3 activity : ~500 kBq/l, 1-2 l/h water inflow, ph-value of 12, no automatic release, filled into containers TSG4: • H-3 activity : ~2.3 MBq/l, up to 20 l/h water inflowin access mode, ~ 2-4 l/h in beam mode, no automatic release, filled into containers, ph-value of 7-8 (neutral) TCV4: • H-3 activity end of 2008: 16 kBq/l  stopped automatic release, contains hydrocarbons  oil separator, up to 30l/h water inflow, access was required frequently (~every 14 days), water filled into containers, end of 2009 H-3 activity 45kBq/l Allowed release if H-3 activity < 6kBq/l (1% of Swiss exemption limit for HTO) 1 Bq = 27 pCi

  4. Tritium mitigation Re-circulating air in TCC4 and TSG4 with an intentional small air leak during operation Big effort to assure that the target chamber remains in an under pressure wrt other areas. Avoid propagation of tritiated air into other areas and in particular being in contact with water ….. improve tightness in the ventilation unit and ventilation pipes and doors Even sealing water drainage system and sumps from air flow coming from the target chamber

  5. Two new sumps in CNGS PGCN • 20-30 l/hr • Release path: • LHC point 8 , River Le Nant, Lake Geneva TAG41 • 2 l/hr TCV4 • 1-2 l/hr Goes into containers TSG4 • 3-20 l/hr 2 new small sumps since 2010 (1m3)

  6. Beginning of 2010: Due to the additional sumps: PGCN sump water (H-3 activity ~ 1kBq/l) could be released automatically. However, the levels of TAG 41 sump water was still too high (>6kBq/l) for an automatic release. (temporary) storage of CNGS container End of 2010: We changed the CNGS ventilation scheme: Access gallery was put in over pressure (compared to CNGS TCC4 and TCV4 chamber). We stopped completely the air leak mode (500m3/h); i.e. no more 500m3/h of air from target chamber into the access gallery. H-3 level in TAG41 < 6 kBq/l  automatic release allowed. Instead of 150 containers/year ... only ~40. No need to empty the sump during operation

  7. Evaporation and Impact Study In 2011 we started to move the containers to the CERN waste center where a evaporator was installed. So far, 55 m3of tritiated water (H3 activity <6kBq/l) has been evaporated. • Impact study: • Determination of the maximum quantity of evaporated water limited by the effective dose to the members of the reference population group • Assumptions: • Dose quota: 1 mSv/year (optimization above 10 mSv/y, taking into account the other sources of exposure of the reference population group) • Quota = (10-6Sv/y) / (1.93  10-20Sv/Bq) = 5.2  1013Bq/y ~50 TBq/year • Currently stored : total activity H-3 = 0.1 TBq corresponding to 2 nSvto the public. ENCON evaporator in ISR3 at CERN

  8. Geographical situation Le Nant SPS Point 4 CNGS air release point CNGS Target chamber LHC Point 8 CNGS water release point

  9. Environment – Regulatory aspects CERN Safety Code F Rev. – Radiation Protection (2006) • Effective dose limit for members of the public: 0.3 mSv/y; • Partitioning: • 0.1 mSv/y  direct exposure to ionizing radiation; • 0.2 mSv/y  exposure due to releases of radioactive substances to air and water; • ALARA: Justification & Optimization: • De minimisdose: <10 µSv/y  a facility is deemed to be justified and optimized; • Attention! 10 µSv/y must not be confused with a dose limit. It is rather a dose constraint or a dose objective. 1 mSv = 100 mrem

  10. Some numbers on H-3 • CERN rain water several Bq/l • CERN detection limit 1.6 Bq/l • Limited’exemption LE (Switzerland) 600 kBq (HTO) .. Ingestion of 1 kg HTO with 600 kBq leads to a dose (E50) of 10 uSv. • Sewage water (Switzerland): • 6kBq/l (weekly average) and 60 MBq (total per month) • Liquid waste (Switzerland): • 600 kBq/l and 60 MBq (total) • Environmental impact: Swiss immissionlimits as a reference; LE/50 i.e. 12 kBq/L HTO on a monthly average. • EU drinking water limit 1000 Bq/l …100 Bq/l under discussion

  11. Water release

  12. Air emissions • The closed HVAC system of the target chamber removes most of the aerosol-bound radioactivity; • The filtration is completed by HEPA filters at the outlet; • Consequences: • Only short-lived radioactive gases (mostly 41Ar) are released at levels worth to consider; • Also HT and HTO pass through but their radiological impact on members of the public is negligible; • However, we did not expect such releases also from the transfer tunnel TI-8! • Lesson learned: In complex tunnel systems, the actual air-flow may be difficult to predict.

  13. Air release

  14. Replacement of Be window Be-window (0.25mm thick, diameter 70mm on 114mm flange) just in front of the target had to be exchanged twice: • Window 1: March 2011 (after 14.34E19 pot): Dose rate (on 12. April 2012): 2000 / 250 uSv/h (contact /10cm) • Window 2: April 2012 (after 4.9E19 pot):Dose rate (on 12. April 2012): 1500 / 200 uSv/h (contact /10cm) Collective dose of exchange of window in 2012: 364 uSv

  15. Traceability of radioactive equipment at CERN (TREC) • Hardware • Buffer zones, workshops etc. are equipped with a PC & 2D barcode reader • Generic, unique, unambiguous traceability labels; • Software • AvailableforhandhelddeviceslikeiPadsoriPhones. • Uses database of existing equipment and locations at CERN • Functionality to create electronic data handling transport request by TREC • E-mail notification to inform when the measurements are completed.

  16. Lessons learned For high intensity fixed-target facilities: • Stray radiation can be minimized by locating the target station deep underground • Ground water activation is ‘easy’ to handle when the facility is located under the ground water table • The impact of releases of radioactive substances to the atmosphere can be reduced by recycling HVAC systems and long delay times before release (long tunnels). Filter removes most of the aerosol-bound radioactivity • In complex tunnel systems, the actual air flow is difficult to predict • Tritium is difficult to ‘contain’, it is very mobile. • Difficult to get rid of tritiated water. • Contamination of water present underground with tritium is a serious challenge but it is rather a PR issue than a RP problem (at CERN).

  17. … something to read of your flight back ? One of the “highlights” The full commented version can be obtained on request from Pavol Vojtyla. E-mail Pavol.Vojtyla@cern.ch Courtesy of Greenpeace

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