Radiation Safety Aspects of the Linear Collider

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Radiation Safety Aspects of the Linear Collider
B. Racky, A. Leuschner, N. Tesch Radiation
Protection Group
TeV Superconducting Linear Accelerator
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Radiation Safety Aspects of TESLA

• Overview TESLA
• Locations of beam loss
• Protection of the public
• exposure limits
• exposure paths

Protection of the staff
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Top view , route on map
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Some data of TESLA
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Side view with earth cover
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Main locations of beam loss
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Calculations of doses and activities
Neutron and Gamma fields

• MC code FLUKA99
• fluence/ dose conversion ICRP

Muon fields

• analytical model
• (1- dimenional transport)

Activity concentrations

• MC code FLUKA99
• (option resnuclei)

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Protection of the Public(local population and
environment)

• Stray radiation fields
• Radioactivity of released tunnel air
• Radioactivity of drinking water
• Activation of soil

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Protection of the Public
planning goal
limit
Sum of all exposures Release of radioactive
air Activation of groundwater Activation of
soil
1 mSv/a
0,1 mSv/a
0,03 mSv/a
0,3 mSv/a
0,03 mSv/a
0,3 mSv/a ?
lt natural activity
?
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Stray radiation fields due to neutrons
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Stray radiation fields due to myons
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Release of radioactive air
Produced Nuclei
Main air activation zone in the tunnel, near
IP 100 kW beam loss (collimators)
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Release of radioactive air
limits
For a mixture of nuclei
ratio lt 0.1
planning goal
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Release of radioactive air
Overview ventilation system S. II-251 TDR
Should it be operated as a closed or open system?
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Release of radioactive air
Tunnel ventilation rate 0,8 m/s, 6104
m3/h length of collimator section 100 m
volume of activation zone 2000 m3 distance to
exhaust station 5 km delay time 1.4 h
data
Ventilation switched off during 1 month
operation, air blown out on each monthly
maintenance day
Closed system
Open system
Ventilation switched on during operation, air
blown out permanently
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Release of radioactive air
Closed system
Sum of all ratios 0.0011 ltlt 1.0 and ltlt 0.1
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Release of radioactive air
Open system
Sum of all ratios 0.26 lt 1.0 but gt 0.1
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Release of radioactive air
A closed ventilation system leads to much smaller
release of radioactivity
Conclusions
Also an open system would fulfill the legal
requirements
Compromise ? open system with bypassed release
stations closed to loss points
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Activation of soil and ground water
in the vicinity of a main dump
wet soil (27 water)
concrete shielding (3 m)
dump
TESLA lumi run Operation time 5000 h (1
year) Energy 250 GeV power 12 MW

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Activity concentration of wet soil
Most relevant nuclei
Sum of all activity concentrations
Bq/g
rings of 50 cm thickness
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Activation of Soil and Groundwater
region of 50 cm around a main dump after 5000 h
of operation
3H 2.60 Bq/g 22Na 0.45 Bq/g
7Be ? Bq/g 22Na ? Bq/g
natural activity 0.3 -1 Bq/g
Dose, consuming 800 l/a 2.5 mSv (? 22Na)
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Transport of ground water
Ground water flow (experts report) area
north dump south
dump descent 1m / 750m
1m/ 900m permeability 5 10-5 m/s
5 10-5 m/s filter velocity 6.7
10-8 m/s 5.6 10-8 m/s distance velocity
2.2 10-7 m/s 1.9 10-7 m/s distance
velocity 6.9 m/ year 6.0 m/ year
error about 80 ?
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Transport of activated ground water
activation zone north dump 12 m south dump
18 m
At what distance is the activity concentration
so low, that drinking 800 l /a results in a
dose of 30 µSv/a ?
After activation
Distance calculations for the dominant nuclide
Na-22
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Zones of activated ground water
5.0 10-6 42 0.3 2.0
10-6 230 3.6 2.2 10-7
78 11 1.0 10-7
42 13
5.0 10-6 280 1.8 3.0
10-6 340 3.6 1.9 10-7
76 13 1.0 10-7
44 14
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Protection of the Staff

• accelerator operation
• stray radiation fields
• (shielding , interlocks)
• maintenance time
• residual radioactivity
• (choice of material, shielding)
• radioactive air
• (ventilation concept)

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Protection of the Staff
Surveyed Areas
limit
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Protection of the Staff
Controlled Areas
limit
local dose rates lt 3 mSv / h
Only temporary access
personal doses lt 20 mSv / a
planning goal
ALARA
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Residual Radioactivity
Hot spots
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Radioactivity of the tunnel air
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Conclusions