Radiation Protection considerations concerning a future SPS dump design Helmut Vincke DGS-RP

Contents Radiological issues with the present LSS1 dump system New beam dump design from the RP point of view Expected gains from an external dump First RP considerations for the design of a new beam dump area

Radiological issues with the present LSS1 dump

Boundary conditions of current dump system Current beam dump system is divided in several single beam dumps 1.High energy particles (TIDV) 2.Low energy particles (TIDH) 3.Injection beam dump 4.Dump receiving “off-momentum” particles (TIDP) TIDV receives the highest beam power (currently ~ 1.0E18 GeV per year) resulting in severe radiation related problems of its surroundings Accelerator equipment and material activation (tunnel, soil, …) Air activation Dose to equipment(especially cables) Further problems arising from the points above (long cool down prior intervention, high dose received by intervening personnel, …)

Accelerator equipment and material activation High activation levels cause high levels of residual dose rate. This leads to: 1.High dose to intervening personnel (e.g. collective dose of LS1 cable exchange: ~ 100 mSv) 2.Long downtimes in case of machine problems in LSS1 3.No trespassing through BA1 during maintenance periods ~25 mSv/h ~3 mSv/h Example: Residual dose rate 30 hours after beam operation in 2010

Air activation Airborne radioactivity produced by the beam dump operation is released close to the building 54 (at the end of TT10). By this air release there are two aspects to be considered: 1.Airborne radioactivity leading to dose to personnel and public. The annual dose received by the critical group of the public in Meyrin is close to 10 uSv (CERN’s optimization limit). Higher intensities on the beam dump would lead to further increased dose to personnel and public 2.Short term high intensity beam dump operation (TIDV): airborne radioactivity release leads to increased ambient dose equivalent rate in the area of building 54 triggering alarm of the gate monitor of CERN tunnel.

Radiation triggered material damage Beam line elements and cables located in the vicinity of the dump area are subject of radiation triggered failures. Higher radiation levels lead to higher dose to equipment (EN can provide more details in that matter)

New beam dump designs from RP point of view

Redesign of internal beam dump in BA1 including its surroundings Desired outcome: the new beam dump design has to significantly reduce all radiation related problems External beam dump Not enough space for required beam dump shielding which would lead to an elimination of the radiological problems Extension of existing tunnel would require significant destructive construction work in high radiation areas Appears as the more promising option Details: see next slides

Expected gains of an external dump LSS1 will become less radioactive Radioactive air production in LSS1 will be significantly reduced Dose to accelerator equipment (e.g. cables) will be reduced Lower dose to personnel Less down time of machine in case of machine problems in LSS1 Less airborne radioactivity released in Meyrin Lower radiation triggered failure rate of material How to reach these gains? Strong majority of particles (especially high-energy protons) have to be extracted from the SPS into a dedicated dump area.

First RP considerations for the design of a new beam dump area

Main RP aspects to be considered for the design of a new beam dump area Prompt dose Activation of material Air activation

1.Dose caused by hadronic and electromagnetic cascade 2.Muon related aspects Prompt radiation Lateral shielding: dump has to be shielded from accessible areas by at least 8 m concrete equivalent (not to be mixed up with shielding minimum for activation aspects). Forward shielding: hadronic and electromagnetic cascade can be easily shielded with a mixture of iron and concrete shielding (~10 m thickness). However, high-energy muons can still trigger significant dose rate problems behind much thicker shielding. Details see next slide. Shielding strategy

Muon dose for 2E18 protons being sent on a Carbon/Iron dump being followed by concrete (hundreds of meters) to stop all muons cm Contour lines show 10, 1000 and 1E5 uSv/year threshold concrete

Activation around new beam dump

First goals to be reached by a new design No access limitation to the area neighboring the dump region Dump needs to be properly shielded First shielding assessments

First activation assessments for shielding requirements considering a TED beam dump 3m 2m TED like beam dump Concrete shielding Calculation result: Residual dose rate after beam dump operation p

Irradiation scenarios considered Cooling times for both scenarios: 1 hour 1 day 1 week 1) Operation: 20 years with 2E18 protons distributed over 365 days 2) Operation: 20 years with 2E18 protons distributed over 365 days followed by 1 day of operation with 5E12protons/s

Residual dose rate after 20 years of operation (2E18 protons per year) followed by 1 hour of cooling

Residual dose rate after 20 years of operation (2E18 protons per year) followed by 1 day of operation with 5E12protons/s + 1 hour of cooling

Residual dose rate after 20 years of operation (2E18 protons per year) followed by 1 day of cooling

Residual dose rate after 20 years of operation (2E18 protons per year) followed by 1 day of operation with 5E12protons/s + 1 day of cooling

Residual dose rate after 20 years of operation (2E18 protons per year) followed by 1 week of cooling

Residual dose rate after 20 years of operation (2E18 protons per year) followed by 1 day of operation with 5E12protons/s + 1 week of cooling

Outcome of first activation studies Summary of assumptions: 1)Annual beam intensity on dump: 2E GeV 2)Dump design: TED + concrete shielding The given dump shielding configuration (lateral: 3 m of concrete; upstream: 2 m of concrete) will reduce the activation production sufficiently to allow immediate access to the areas located outside the shielding wall. In case of space limitation the proposed concrete shielding can also be replaced by a 50 cm concrete + 1 m iron + 50 cm concrete shielding configuration. However: 1.when being dismantled the iron blocks will be more radioactive than the concrete blocks  higher dose rate + more expensive disposal No RP fine tuning for material choice of TED or shielding was carried out so far. ActiWiz to be used for fine tuning of material choice (see:

Air activation No dedicated air activation were studied so far First assessment (based on experience) concerning airborne radioactivity: Preventing immediate air release of the region inside the shielding a strong reduction in dose-to-environment can be expected. Location of air release is certainly of importance

Dose to accelerator equipment Typical accelerator equipment located outside the shielding has little risk to be harmed by the beam dump operation. Details to be studied by colleagues from EN

Conclusion The existing beam dump system of the SPS is problems in terms of 1.Material activation 2.Airborne radioactivity production 3.Radiation triggered equipment damage For an SPS beam dump upgrade an external beam dump solution should be chosen Possible future dump operation scenarios: All particles are extracted from the SPS  ideal solution All high-energy particles are extracted from the SPS  good solution Only the LHC beam is extracted to the external dump  still highly radioactive BA1 area + new highly activated external beam dump + shielding First RP consideration for a new beam dump design: Prompt radiation: shielding between dump and accessible areas: minimum of 8 m lateral shielding m of concrete equivalent to reduce muon radiation (dump should not point upwards). Material activation: 3m concrete equivalent shielding will allow immediate access to areas outside dump shielding Air activation: details to be studied. Certainly improved situation compared to current beam dump.

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Dose rate as a function of cooling time Dose rates are measured at ~ 70 cm distance to elements TIDV dump Area downstream TIDV dump Area downstream TIDP dump TIDP dump

Dose rate as a function of cooling time, long term perspective Dose rates measured close to the hot spot of the equipment can be considerable higher Even after long cooling times dose rates are still in the mSv/h range.

ActiWiz 1.) Select parameters of the material location in the accelerators 2.) Define material composition 3.) Click “Calculate” 32 Program to evaluate radiological hazard for arbitrary materials with a few mouse clicks

Output of ActiWiz: Material categorization 33 Radiological hazard assessment of materials allowing to compare their radiological impact Aluminum 5083 Copper CUZnO5Steel 316Ti Operational Waste

Material catalogue based on the ActiWiz hazard assessment of materials Material catalogue classifying materials in terms of radiological hazard Classification of most common metallic and construction materials used at CERN 34 Catalogue provides guidelines for selection of materials to be used in CERN’s accelerator environment Authors: Robert Froeschl, Stefano Sgobba, Chris Theis, Francesco La Torre, Helmut Vincke and Nick Walter Acknowledgements: J. Gulley, D. Forkel-Wirth, S. Roesler, M. Silari and M. Magistris

Web-based catalogue: ActiWeb 35 Information and a download area about ActiWiz, the RP material catalogue and ActiWeb can be found under: Interactive web-based version of catalogue allowing you to compare the radiological impact of predefined materials