1. Neutronics & RP Issues Neutronics & RP Issues nToF Review 14 th February 2008 CERN AB/ATB/EET n_TOF Team

2. nToF Review 2008 - Neutronics & RadioProtection2 February 14th 2008 Overview Experience from the Existing Target  Activation measurements  Comparison with FLUKA  Consequences for design choices New Target Design  Critical Design Questions concerning: Target support material Additional target alloy materials Target cooling Area ventilation  Impacts to be Studied for Neutronics Radio Protection Issues  activation and residual dose rates  handling  radioactive waste concerns  air activation and dose to the public

3. nToF Review 2008 - Neutronics & RadioProtection3 February 14th 2008 Geometry Implementation  the simulation includes a detailed layout and design, for both the target and the tunnel up to the experimental area New Design Options  quick flexibility to change design parameters and estimate respective influences Detailed Estimates concerning  neutron fluences (physics)  energy deposition (engineering design, cooling)  isotope production (radioactive waste, air activation)  residual dose rates (handling, waste) Accuracy  well benchmarked code in all required fields FLUKA Calculations

4. nToF Review 2008 - Neutronics & RadioProtection4 February 14th 2008 Geometry Details

5. nToF Review 2008 - Neutronics & RadioProtection5 February 14th 2008 Target in the Pit Target Earth Pit filled (concrete) Beam Pipe Concrete Marble Beam

6. nToF Review 2008 - Neutronics & RadioProtection6 February 14th 2008 X Z Y Beam Entrance Beam Exit n_ToF Experimental Area Target outside the Pit (arb. location) Important for 2-Step calculations e.g., used for inter- comparison with final activation measurements

7. nToF Review 2008 - Neutronics & RadioProtection7 February 14th 2008 Chemical Composition  accurately known for the used lead (e.g., 19ppm Bi)  for steel: first estimated based on preliminary dose rate measurement and finally evaluated during the target removal Irradiation History  beam intensity and irradiation time profile are accurately known Geometry  implemented in a very detailed way MC Calculation  extensive calculations (computer cluster) FLUKA Models – Activation/Residual DR  well benchmarked for low/medium-mass materials at CERF  recent comparison for high mass isotopes show a very good overall agreement Important Input Parameters

8. nToF Review 2008 - Neutronics & RadioProtection8 February 14th 2008 Neutron Fluence - Benchmark 20% difference between 1 and 1E5 eV ??? Performance Report CERN-INTC-2002-037, January 2003 CERN-SL-2002-053 ECT

9. nToF Review 2008 - Neutronics & RadioProtection9 February 14th 2008 Preparing for Lead target dismount Discovery that the water layer is 6 cm thick instead of 5!!! New FLUKA simulations with + 6 cm water (red) compared with + 5 cm (black) Neutron Fluence - Benchmark -> Perfect Agreement

10. nToF Review 2008 - Neutronics & RadioProtection10 February 14th 2008 Experimental Area: Neutron Fluence The energy resolution is dominated by the 5cm of water with the resolution experiencing a peak and a tail at low energies  the peak being determined by the water moderation (width ~= 2cm)  the tail is due to the interface lead/water The resolution inside lead has delta-lambda of about 30cm with an absolute position lambda equal to 5.7m Anything more than 5cm of water produces the same resolution

11. nToF Review 2008 - Neutronics & RadioProtection11 February 14th 2008 Inspection & Measurements

12. nToF Review 2008 - Neutronics & RadioProtection12 February 14th 2008 First Dose Rate Survey Pit survey with dose rate meter attached to a cord and reading the maximum recorded value Target survey with manual reading and measurements for a predefined set of locations First comparison with FLUKA showed a significant disagreement 10.3 m Decay tube Rectangular section pool Circular section Square section

13. nToF Review 2008 - Neutronics & RadioProtection13 February 14th 2008 Important Findings & Changes Pit & Target  update of geometry (container, support, 30cm, steel faces) Pit  new survey with special dose rate meter and laser controlled distance  negligible contribution to residual dose rates coming from contamination Target  detailed survey with special dose rate meter  chemical composition stainless steel – cobalt content important influence on residual dose rate distribution (up to a factor of 25 in the possible concentration range) a cobalt content of 0.1% results a very good agreement (this concentration value is confirmed by existing steels at CERN)

14. nToF Review 2008 - Neutronics & RadioProtection14 February 14th 2008 Inside the pit: using a laser attached to the crane to control the position of the remote detector (attached to the hook) Around the target: same method, starting at 3 meters distance & going towards the target surface. (fully remote, thus possibility to wait & get enough statistics while performing continuous measurements) Detailed Dose Rate Survey

15. nToF Review 2008 - Neutronics & RadioProtection15 February 14th 2008 New FLUKA Comparison after Detailed Pit Survey Measurements 01.11.2007 0.1 1 10 100 1000 10000 0200040006000800010000 Distance from the Top (Access Gallery) / mm Residual Dose Rate /  Sv/h Detailed Measurements FLUKA New Simulations First FLUKA Simulations First Measurements FLUKA Simulation Upper Shaft Lower Shaft Target Decay-Tube Container r Target Decay-Tube Lower Shaft Upper Shaft

16. nToF Review 2008 - Neutronics & RadioProtection16 February 14th 2008 Residual Dose Rates Comparison

17. nToF Review 2008 - Neutronics & RadioProtection17 February 14th 2008

18. nToF Review 2008 - Neutronics & RadioProtection18 February 14th 2008 Steels used at CERN Cast No E33408, Nippon Steel, Inspection Certificate (F.Bertinelli, used for LHC) Density 7.252 g/cm 3 CERN store 44.57.10.420.4 SCEM: 44.57.10.420.4, INOX RNDS.304L Density 7.908 g/cm 3 EA: ICP-AES (AES=Atomic Emission Spectrometry) EMPA: WD-XRF (wavelength-dispersive X-ray fluoresence spectrometry) EIG: XRF In addition, direct measurements on the target steel support will be performed (measurement device is ordered and soon to arrive at CERN)

19. nToF Review 2008 - Neutronics & RadioProtection19 February 14th 2008 Dependency on Cobalt Content Using a stainless steel type with low Co 59 content will be important for the new target design

20. nToF Review 2008 - Neutronics & RadioProtection20 February 14th 2008 Impact on Design

21. nToF Review 2008 - Neutronics & RadioProtection21 February 14th 2008 Peak Energy Density - Dilution  Increase in beam size Target materials  Additional target alloy materials (Sb, Ag, PbO) influence in neutron production (Neutronics) impact on isotope production and residual dose rates Target support  choice of material (Al, SS, Special) impact on residual dose rates  additional means to reduce residual dose rates Cooling  Installation of cooling system residual dose rates and accessibility  Activation of water handling and radioactive waste Area ventilation  installation of ducts and influence on prompt dose rates upstairs prompt dose rates and area classification Critical Design Questions

22. nToF Review 2008 - Neutronics & RadioProtection22 February 14th 2008 Increasing the Beam Size Factor of ~10

23. nToF Review 2008 - Neutronics & RadioProtection23 February 14th 2008 Residual Dose Rates

24. nToF Review 2008 - Neutronics & RadioProtection24 February 14th 2008 Possible constraint during installation of the piping system Same constraint possibly also during target removal Lowest plug will remain in place Final technical solution might require short interventions to manipulate the connection flanges Very low dose rates for both short and long operation scenarios Connection of Cooling System 6m + 5m10y + 1y  Sv/h

25. nToF Review 2008 - Neutronics & RadioProtection25 February 14th 2008 Calculation Methods  “One-Step” simulation looking at residual dose rate distributions when the target is in its lower pit position  “Two-Step” calculations resulting in 3D residual dose rate maps around the target only (without surroundings)  For both: different operation and cooling times Support Materials  Aluminum  Stainless Steel with 0.1% / 0.03% / 0.01% Cobalt Target materials  Standard ‘very pure’ lead  Addition of Sb (3%) Additional “Shielding”  Borated polyethylene plates (10cm, side and entry face) with 6% natural boron, i.e., about 1% 10 B Target Support Material Choice

26. nToF Review 2008 - Neutronics & RadioProtection26 February 14th 2008 Target Support Material Aluminum ContainerSteel Container 6m + 5m  Sv/h

27. nToF Review 2008 - Neutronics & RadioProtection27 February 14th 2008 Target Support Material Aluminum ContainerSteel Container 10y + 1y  Sv/h

28. nToF Review 2008 - Neutronics & RadioProtection28 February 14th 2008 Target Support Material (Steel/0.1%Co) “Shielded” with Boron 6m + 5m Standard Container  Sv/h

29. nToF Review 2008 - Neutronics & RadioProtection29 February 14th 2008 10y + 1y Standard Container Target Support Material (Steel/0.1%Co)  Sv/h “Shielded” with Boron

30. nToF Review 2008 - Neutronics & RadioProtection30 February 14th 2008 Target Material Lead with 3% Sb 6m + 5m Standard Lead  Sv/h

31. nToF Review 2008 - Neutronics & RadioProtection31 February 14th 2008 10y + 1y Standard Lead Target Material Lead with 3% Sb  Sv/h

32. nToF Review 2008 - Neutronics & RadioProtection32 February 14th 2008 Comparison (20cm distance) x “Boron Shielding” “Sb Alloy”

33. nToF Review 2008 - Neutronics & RadioProtection33 February 14th 2008 Target Only – Two-Step Calculation Lateral Cut - CentreLongitudinal Cut - Centre 10y + 1y ~20 mSv/h ~2 mSv/h (Standard Lead + Stainless Steal Container with 0.1% Cobalt)  Sv/h

34. nToF Review 2008 - Neutronics & RadioProtection34 February 14th 2008 Target Only – Two-Step Calculation Std. Pb + SS with 0.1%Co 10y + 1y ~20 mSv/h ~2 mSv/h Pb + 3%Sb + SS with 0.01%Co  Sv/h

35. nToF Review 2008 - Neutronics & RadioProtection35 February 14th 2008 Base Material Choice  Aluminum would be best, however stringent constraints in terms of structural disadvantages corrosion issues poses problems for radioactive waste treatment  Stainless steel is favorable, especially in case special steels with low (~0.03%) cobalt content can be found Additional ‘Shielding’  The basic principle is to get into ‘competition’ with 59 Co in terms of low- energy neutron capture, by following one of the following approaches borated poly-ethylene (6% natural boron) -> studied in terms of “proof of principle” possibility to use borcarbid plates addition of boron in the cooling circuit Addition of Sb into the Lead  Augmentation of residual dose rates for short cooling times due to important production of 124 Sb Material Choice

36. nToF Review 2008 - Neutronics & RadioProtection36 February 14th 2008 Neutronics

37. nToF Review 2008 - Neutronics & RadioProtection37 February 14th 2008 Influence of Target Alloy Materials New Target: +3% Sb, 0.01% Ag

38. nToF Review 2008 - Neutronics & RadioProtection38 February 14th 2008 Influence of Target Alloy Materials New Target: +3% Sb, 0.01% Ag

39. nToF Review 2008 - Neutronics & RadioProtection39 February 14th 2008 Neutronics – Boron ‘Shielding’

40. nToF Review 2008 - Neutronics & RadioProtection40 February 14th 2008 Neutronics – Different Configurations

41. nToF Review 2008 - Neutronics & RadioProtection41 February 14th 2008 Neutronics – Different Configurations

42. nToF Review 2008 - Neutronics & RadioProtection42 February 14th 2008 Ventilation Issues

43. nToF Review 2008 - Neutronics & RadioProtection43 February 14th 2008 Critical Group: Border Guards Critical Groups Target Experimental Area Decay Tube

44. nToF Review 2008 - Neutronics & RadioProtection44 February 14th 2008 FLUKA simulations to calculate the isotope production yield (39 different isotopes considered) Exposure of personnel (access to nToF area)  Dose conversion coefficients based on the Swiss and French legislation Dose to the public (outside CERN)  Definition of critical groups (border guards)  Calculation of dose conversion coefficients (P. Vojtyla) based on environmental models Different ventilation scenarios  Existing situation  Continuous ventilation (laminar flow)  Enclosed area and flush before access (full mixing) Best solution  Enclosed area, continuous filtering during operation and flush before access, leading to annual doses below 0.1  Sv Annual Dose Calculation

45. nToF Review 2008 - Neutronics & RadioProtection45 February 14th 2008 A full 3D simulation being too time consuming we decided for a two-folded approach combining in a first step detailed simulation followed by a second analytical calculation  Calculating the prompt equivalent dose rate in the tunnel below the expected location of the ventilation duct (~40m downstream)  Using analytical ‘over the thumb’ formulas to calculate the attenuation for a given duct Considered parameters  position: 40m downstream  duct is 5m long  40cm diameter  straight line  dose reduction as ‘line of sight’ in front of the duct and directly behind Installation & Streaming through Ducts

46. nToF Review 2008 - Neutronics & RadioProtection46 February 14th 2008 Lateral to the ventilation duct a maximum prompt dose rate in the order of 100mSv/h can be expected Assuming a ventilation duct with 5m length and 40cm diameter one expects a reduction by about three orders of magnitude Resulting at the top in a prompt residual dose rate of about 100  Sv/h Streaming Calculation Sv/h X X

47. nToF Review 2008 - Neutronics & RadioProtection47 February 14th 2008 Radioactive Waste

48. nToF Review 2008 - Neutronics & RadioProtection48 February 14th 2008 Comparison between  the existing target (4 years of operation & three years of cooling)  with the new design (10 years of operation & one year of cooling) Total activity and specific activity increase, however in acceptable margins  increased operation, shorter cooling time  significant reduction in total mass (factor of ~4) Alpha emitters are largely below ATA levels Activation of Target, Support & Water

49. nToF Review 2008 - Neutronics & RadioProtection49 February 14th 2008 Conclusions

50. nToF Review 2008 - Neutronics & RadioProtection50 February 14th 2008 Conclusions Careful Evaluation of FLUKA Simulations  The detailed measurements performed during the target removal and inspection interventions allowed for a careful benchmark of the simulations Peak Energy Density - Dilution  The increase in beam size reduces the peak energy density by about a factor of 10 Target materials  Additional target alloy materials (Sb, Ag, PbO) No significant influence in neutron production No significant impact on isotope production in terms of waste disposal Significant increase in residual dose rates for short cooling times (< one year), however no “show-stopper” in terms of handling and possible advantage for long cooling times (competition reaction with 59 Co) Target support  choice of material (Al, SS, Special) and additional means to reduce residual dose rates Low-Cobalt stainless steel combined with a possible implementation of a “Boron-Shielding” (e.g., Borcabide plates) would be an optimum solution

51. nToF Review 2008 - Neutronics & RadioProtection51 February 14th 2008 Conclusions Neutronics  Neutron fluxes were verified for all studied design options and no ‘show-stopper’ was found  Ensuring an optimum water layer thickness of 5cm Cooling  Installation of cooling system Residual dose rates were checked and accessibility is guaranteed at all times Area ventilation  Acceptable levels of prompt dose rates are introduced at the location of the ventilation station  Envisaged ventilation system minimizes dose to the public to an absolute minimum Radioactive Waste  Target is optimized in terms of mass (reduction by a factor of 4) and the reduced amount of cooling water eases future disposal

52. nToF Review 2008 - Neutronics & RadioProtection52 February 14th 2008 Thank You