Radiation Studies for the operation of HiRadMat/SPS facility

N. Charitonidis (CERN/EPFL), C. Theis (CERN), H. Vincke (CERN), I. Efthymiopoulos (CERN)

Introduction• HiRadMat radiation issues are very challenging, due

to the nature of the facility• Detailed Monte-Carlo studies, using the FLUKA code

have been performed for several possible, operational, and worst-case scenarios for all the tunnels (TNC, TJ7, TA7, PA7) and surface buildings

• Apart from this presentation, an EDMS internal note is being prepared.

• The activation and background radiation has been calculated for seven cooling times, up to 2 months

• Specific calculations have been performed for the possible activation of the water-cooling circuit.

Geometry & drawings• The most challenging part was the

implementation of the real tunnels and buildings geometry using FLUKA’s combinatorial geometry.

• The drawings in some cases were really old and difficult to find.

• It is not always possible to model all the details of the actual geometry using only simple shapes

A very detailed geometry

2010

TNC

TT61TJ7

TA7

PA7

BA7

TCC6

19752010

2010

Thanks to: I. Efthymiopoulos, A. Pardons, C. Magnier, O. Choisnet, S. Evrard, D. De Paoli for answering my numerous requests for drawings and details!

FLUKA model

T9 dump (modeled by A. Christov)Ventilation

Stair-case and elevator holes

Magnets & beam elements test stand + collimator

Bt. 876 Bt. BA7

PA7

Bt. 846

• The dimensions of the tunnels and the “tunnel findings” are in almost perfect agreement with the drawings

• For the estimation of the BA7 dose, the PA7 geometry was modelled in detail (staircase and e/m installations)

Several Scenarios• Prompt studies (A copper target, 1m length, placed

at focal point 1 (representing a worst-case scenario)

• Activation studies (operational scenario with the table and the collimator placed in focal point 3)

• Background studies (when the activated objects are removed, the remnant dose at the tunnel)

BA7 Geometry modeling

BA7 roof

Bt. 876Internal shaft room

Hole cover (Iron, 1cm)

Roof “blind” point

Soil around (standard compound composition) and natural air surrounding the buildings

BA7 Geometry modeling

BA7, inside the internal

shieldingIron plate

covering the hole

Staircase

The hole of the elevator

installation.

The cables and electromechanical infrastructure of

the shaft

Irradiation Parameters• For the worst case scenario a copper target of

3cm radius and 1 meter length, accepting the full beam.

3# 3.6 10#

pSv p Svp extr duration h

• The results by FLUKA are given in pSv/primary. So a normalisation factor of the following form was applied:

• The worst beam scenario is 4.89E15 protons over 100 extractions of 20s each.

BA7: Prompt Dose

On average < 0.5 μSv/h out of the internal wall

70-200 μSv/h

The area outside the internal shielding can be characterized as “Non designated area”

Negligible prompt dose rates in all accessible areas

μSv/h

BA7 roof prompt dose• In case of some needed intervention during

the facility operation in the BA7 building roof, the prompt dose rate was calculated.

1 – 10 nSv/h for the worst case

scenario. Negligible

μSv/h

BA7 roof prompt dose (“weak” point)

Weak point on the roof of BA7.

Negligible prompt radiation.

Also the prompt radiation levels in building 876 are in compliance with a non-classified area .

TNC tunnel calculations - PROMPT

Beam line elements

T9 dumpCopper target

Iron blocks

Ventilation

10-40 kSv/h~ 100 Sv/h

Worst case scenario ( 4.89E15 protons over 100 extractions of 20s each). Prohibited area during operation

TNC tunnel calculations - Activation• Irradiation profile chosen : Short SPS cycle, 1.98E12 p/s for 504 s (~1e15 protons)• Seven cooling times: 1 hour, 1 day, 2 days, 1 week, 1 month, 3 months.• Exemplary operation scenario: The beam hits the carbon jaw of a typical collimator, placed on the test stand

T9

The third stand table was modeled to be at focal point 3.

TNC tunnel - Activation

• Cooling time of 1 hour

μSv/h

• Cooling time of 1 day

μSv/h

1-5 mSv/h near the collimator

10-50 mSv/h

TNC tunnel - Activation

• Cooling time of 1 week

• Cooling time of 1 month

μSv/h

75μSv/h

~ 1 μSv/hnSv/h

μSv/h

1mSv/h

Near the collimator• Since interventions may be necessary near the

activated object, some typical values are given:

Position “upstream”: 50 cm from the collimator

Position “middle”:

40cm from the end

of the collimatorPosition “downstream”: 30 cm from the collimator

Position “lateral”: 40 cm from the collimator

Detailed model of the stand table.

Dump

Near the collimator [μSv/h]Position/

Cooling timePosition

“upstream”Position “middle”

Position “downstream” Position “lateral”

1 hour 4E4 1E6 3E4 7E412 hours 1.5E3 4E4 2E3 4.5E3

1 day 800 2E4 1E3 2.5E32 days 360 1E4 500 1E31 week 90 5E3 130 450

1 month 20 1E3 30 1102 months 10 550 15 50

TNC tunnel – Background dose

• Using the latest version of the code, we calculated the background (remnant) dose at the tunnels, i.e when the activated object is removed

• Again the same 7 cooling times where used.

• Scenario: A “small” copper target (15 cm length) was placed at focal point 3 (closer to the dump), with an irradiation scenario of 1E16 protons over 1 year.

TNC Tunnel - Background• Cooling time of 1 hour

μSv/h

~ 150μSv/h

~ 5μSv/h

• Cooling time of 1 day

μSv/h

The contribution on the background dose is mainly from the activation of the dump

TNC Tunnel - Background• Cooling time of 1 month

μSv/h

~ 16 μSv/h

• Cooling time of 2 months

μSv/h

TJ7 tunnel : Prompt Dose

~ 20 Sv/h ~ 40 Sv/h

• Worst case scenario : 4.89E15 protons over 100 extractions of 20s each

Access to TJ7 during operation : PROHIBITED

• Even for the long SPS cycle (1E15 protons over 30 extractions of 44s each

~ 10 Sv/h~5 Sv/h

TJ7 tunnel - Activation Dose• Same activation scenario as for the TNC tunnel - Short SPS

cycle, 1.98E12 p/s for 504 s (~1e15 protons) – beam on the carbon jaw of the collimator

• The same cooling times (1 hour, 1 day, 2 days, 1 week, 1 month, 3 months)

• Radiation levels due to activation are not extremely high in TJ7 but they are not negligible in all cases.

TJ7 tunnel - Activation

• Cooling time of 1 day

Ventilation TNC

~ 40 μSv/h

• Cooling time of 1 hour

~ 2 - 5 μSv/h

Water activation calculations• Activation of the water circuit had to be

studied in order to get sure that we are complying with the legal limits.

• Two scenarios were studied: a) Beam simulated to hit directly the TED core (worst-case)b) Beam simulated to “scrape” on the collimator

• Assumptions:i) The water in the dump is homogenously mixed with the rest of the water

cooling circuitii) The total volume of the water in the circuit is 60000L while the volume of the

water in the dump is 4.779L. Dilution factor: 7.97E-5iii) FLUKA underestimates H-3 by a factor of 2.54 * * J. Vollaire, M. Brugger, D. Forkel-Wirth, S. Roesler, P. Vojtyla, Calculation of Water Activation for the LHC, Nuclear Instruments and Methods in Physics Research A 562, pp. 976-980, (2006)

Water Activation• Worst case scenario (beam directly in the dump

core) 1016 protons over one year

Isotope τ1/2 Specific Activity [Βq/L]3H 12.4 y 102

7Be 53.3 d 198

1017 protons over ten yearsIsotope τ1/2 Specific Activity [Βq/L]

3H 12.4 y 80507Be 53.3 d 1999

Everything within the limit, except H-3 in the disaster scenario ! ! !

Limits: 6000 Bq/L for 3-H and 4000Bq/L for 7-Be

Water Activation• Operational scenario (beam on the collimator)

1016 protons over one yearIsotope τ1/2 Specific Activity [Βq/L]

3H 12.4 y 457Be 53.3 d 88

1017 protons over ten yearsIsotope τ1/2 Specific Activity [Βq/L]

3H 12.4 y 3537Be 53.3 d 89.5

Values well bellow the limits for the operational scenario

Limits: 6000 Bq/L for 3-H and 4000Bq/L for 7-Be

Conclusions• During the operation, access to the underground

areas is prohibited. However, presence in the accessible areas in bt. 876 and the surroundings of bt. BA7 is possible due to the surface shielding of the shaft.

• When there is no beam, controlled access to BA7 and PA7, TA7 and TJ7 tunnels can be possible.

• Attention should be paid to the activation of the dump. It will act as a source, contributing significantly to the residual background dose rate after an experiment.

• The risk of water activation is very low and the levels will be monitored.

Thank you !