First radiological estimates for the HIRADMAT project

H. Vincke and N. Conan

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Contents

1. Results of the radiation survey around the WANF target area (2008)

2. Collective dose to be expected for a WANF area dismantling

3. Residual dose rates to be expected in the empty WANF area

4. Residual dose rates to be expected from the HIRADMAT beam operation

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6.5

Old TAX blocks storage

100 65

300

900400 at 40 cmDose Rate in µSv/h 300

260

5 to 10

• Dose rate inside and downstream the target shielding will be significantly higher than 1 mSv/h

• Gamma spectroscopy of concrete samples taken in the area showed that the concrete tunnel structure is radioactive

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Dismantling of the WANF AREA

• The WANF facility was already once fully dismantled in 1992.

• For the removal of the old WANF beam line a collective dose of 210 mSv was taken by the personnel. The full refurbishment of the area caused an additional collective dose of 170 mSv.

• According to reports from that time, the residual dose rate in the area of the target was at least 2 times higher than today.

• Hence, as a first order estimate we can expect a collective dose which is a factor of 2 lower than the one received in 1992.

• From the RP point of view it is recommended that the zone is dismantled. The dose rate will not drop substantially in the next 10 years. However, the area conditions (rust, dirty) worsen with time.

• Space for the radioactive WANF material still has to be found. Hence, a reuse of radioactive material (e.g.: WANF target station) in the beam dump is advisable.

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First radiation studies concerning the radioactivity level of the empty WANF area (after removal of the WANF beam

line equipment)

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Procedure to obtain dose rate results considering the concrete only

• The dose rate of the concrete cannot be measured directly:

• The surrounding beam line elements are highly radioactive and overshadow the dose rate coming from the concrete

• The concrete with the highest radioactivity is inaccessible (blocked by beam line components)

•FLUKA simulations have to be conducted to obtain first ideas about the radioactivity level of the empty area.

• Drawbacks: the simulation results are only as good as the input parameters of the simulations: • Details of geometry (target and shielding parameters)• Concrete composition (real composition unknown, typical CERN concrete was used in the simulations)

Results should be seen as indication and not as accurate number6

FLUKA simulation geometry used for the WANF simulations

Tunnel

Target station

110 m

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Details of target station used in simulation(Information taken from ACAD file, received from M.

Lazzaroni)

Iron shielding

Marble shielding

Be-target

Beam

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Simulation procedure to obtain residual dose rate in the empty tunnel

Two steps:

1. Simulation of the beam impact in the target producing a radionuclide “inventory” in the concrete tunnel. Beam parameters used : 10 years of operation (2E19 protons per year) + subsequent cool down of 10 years.

2. Simulation of the decay of radionuclides (beta or gamma emission) in the concrete considering only the empty beam tunnel (without beam line elements) dose rate map

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Dose rate profile in the empty WANF tunnel (after removal of beam line)

Position of target station

Radiation in this area might be considerably higher since beam line equipments in this area were not taken into account in this first estimate

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Profile taken over y = 60, x = 180, along the beam line

x

yz

Dose rate (uSv/h) seen by a person (1.8 m) walking through the empty tunnel

Location of Target station

Profile taken over y = 60, x = 180, beside target station

Most preferable place for installation work can be found upstream the target station. 11

In case HIRADMAT cannot be installed upstream the WANF target station location

Bypass tunnel leading to low radiation location

Tunnel made of40 cm concrete walls + 20 cm concrete floor reduces dose rate from 200 uSv/h to 5 uSv/h

Tunnel made of40 cm concrete walls (no additional floor) reduces dose rate from 200 uSv/h to 60 uSv/h

Effect of bypass tunnel

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Generic studies concerning residual dose rate levels caused by the future HIRADMAT collimator

irradiation

Estimates are based on the report “CERN-SC-2004-018-RP-TN”:Remnant dose rates in the area of a TCDI collimator after 200 days of normal operation and after an accidental beam loss;

Helmut Vincke

2 irradiation scenarios

1.Short term scenario: impact of 10 subsequent full SPS beam cycles (3.3E13 protons per cycle)2.Long term scenario: 1E16 protons equally distributed over 200 days

5 cooling times1. 1 hour2. 12 hours3. 1 days4. 1 week5. 1 month

Beam

Concrete wall

TCDI (carbon) collimator

Beam line elements

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10 full SPS beam cycles (3.3E13 protons per cycle)

1E16 protons equally distributed over 200 days

Cooling time

Dose rate between wall and beam line

Dose rate maximum

value

Dose rate between wall and beam line

Dose rate maximum

value

1 hour 26 mSv/h 1.3 Sv/h 800 Sv/h 32 mSv/h

12 hours 2 mSv/h 66 mSv/h 600 Sv/h 24 mSv/h

1 day 660 Sv/h 15 mSv/h 480 Sv/h 20 mSv/h

1 week 66 Sv/h 3.3 mSv/h 280 Sv/h 12 mSv/h

1 month 26 Sv/h 0.7 mSv/h 200 Sv/h 6 mSv/h

Summary for full loss and operational scenario

• The dose rate level in the tunnel after one year of operation is higher than the dose rate in the empty WANF tunnel.

•The long term irradiation levels are mainly caused by the two elements installed in the beam line and not by the concrete walls

•In case the carbon jaws are replaced by copper or tungsten jaws, the dose rate will increase significantly

Dose rate after1E16 protons in 200 days + 1 month of cooling

4.0E+041.8E+048.8E+034.0E+031.8E+038.8E+024.0E+021.8E+028.8E+014.0E+011.8E+018.8E+004.0E+001.8E+008.8E-014.0E-011.8E-018.8E-024.0E-021.8E-028.8E-034.0E-03

mSv/h

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Summary

• WANF area is still radioactive

• From the RP point of view it is recommended to dismantle the WANF area. Storage space for radioactive waste has to be found. Radioactive material (e.g.: WANF target station) should be reused as beam dump.

• In terms of the radioactivity distribution in the WANF area it would be preferable to install HIRADMAT upstream the target location

• Residual dose rates caused by one year of HIRADMAT operation (generic model) was calculated to be higher than the current dose rate of the empty WANF tunnel

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END

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Arguments against installation in TI8 (TJ8) or TT40 area

• LHC and CNGS beam goes through the same area• Due to the high dose rate around the equipment after the test, operation of LHC and CNGS will be jeopardized in case beam line equipment has to be repaired in the surroundings of the test area• Significant waiting times before installation have to be expected • Due to these reasons test areas should be installed in dedicated areas only• The same argument can also be used for the installation close to the T1 target position in TT60/TI2 area (option B in Ilias’ presentation).

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Residual dose rate comparison between tungsten and carbon

jaws

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1E13 protonsIrradiation time: 2d , cooling time: 1d

Hot spot: ~ 13000 uSv/h

Tungsten collimator

Carbon collimator

Hot spot: ~ 460 uSv/h

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1E13 protonsIrradiation time: 2d , cooling time: 1w

Hot spot: ~ 1500 uSv/h

Tungsten collimator

Carbon collimator

Hot spot: ~ 150 uSv/h

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1E13 protonsIrradiation time: 2d , cooling time: 1m

Hot spot: ~ 220 uSv/h

Tungsten collimator

Carbon collimator

Hot spot: ~ 40 uSv/h

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