KEK Radiation Related Topics

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KEK Radiation Related Topics
Yuichi Oyama (KEK)
for

• neutrino beam construction subgroup

and
target monitor subgroup
Nov-11-2003_at_NBI2003
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Contents
(1) Proton beamline
(2) Target Station

• beam period

• after beam stop

• maintenance

(3) Decay Volume
(4) Beam dump / Muon pit
(5) Cooling water
(6) Air/Helium
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Radiations in the Proton Beamline
Following energy loss are assumed from our
experience.
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Arc Section
Preparation Section
0.75kW point loss
1W/m line loss
H lt 5mSv/h (line loss) and
Regulations
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H lt 11mSv/h (point loss) at
boundary of the concrete
H lt 0.25mSv/h at surface
of the Soil
Soil
Final Focusing
0.25kW point loss
Concrete
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Example Shielding around the tunnel
The thickness of the shielding is calculated by
the Moyers formula and MARS simulation.
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1.2mSv/h
0.25mSv/h
6.2m soil
11mSv/h
5.6m soil
2.5m concrete
0.05mSv/h
2.3m concrete
5.0m air
2.5m air
Arc section
Final Focusing section
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Example Radiation in the Access Tunnel
For more complicated geometry, MARS simulation is
employed.
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H0.5mSv/h
The graphical view of the calculation shows that
the kink of the access tunnel effectively
reduce the radiation.
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Schematic view of the Target Station
22m
33m
Surface building
40tonne crane
11m
ground level
Concrete
Concrete
service pit
Beam Window
Final Focusing section
Iron Shielding
Underground machine room
Decay Volume
Helium Container
storage of radioactive materials
Beam Window
Concrete
Iron Shielding
Buffle
Target, 1st Horn
2nd Horn
3rd Horn
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Radiation during the beam operation
Regulations
Three
must be satisfied.
20cm Concrete wall
fence
H lt 12.5mSv/h_at_floor of surface building
(1)
(3)
H lt 0.25mSv/h_at_out of the control area
Concrete 4.5m
Conc 1m
Iron2.2m
Iron1.5m
H lt 5mSv/h_at_boundary of the concrete
(2)
Iron1.5m
Concrete 3.6m
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Calculation of shielding thickness by MARS
Instead of 3D real geometry, virtual cylindrical
geometry is used to improve statistics.
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Calculation with 3D real geometry are in progress
for the final confirmation.
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Example floor of the surface building
Target station
r
z
With 4.5m of concrete above the service pit,
radiation at floor of the surface building
satisfy H lt12.5mSv/h
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Determination of the control area boundary by MCNP
Neutron sources are defined on the floor, and the
dose above the floor is adjusted to be 12.5mSv/h.
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Surface building
Top view
12.5mSv/h
0.25mSv/h
We need 10m between the surface building and the
fence
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Radiation Control Area
????
Target Station
Control area (class-1)
2nd machine room
Control area (class-1)
Control area (class-2)
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Residual Dose after beam stop
After beam stop and ventilation,
we must access this area
Service Pit
Machine room
After 1 year operation and
1 day cooling with 0.75MW,
the residual dose at the top of the iron
shielding is
0.1 mSv/h
We can enter and work in the service pit.
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Exchange of the target and/or horn
Open the top of the beamline shielding
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Broken target/horn is highly radioactivated, and
must be kept in the storage of radioactive
materials for several years.
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The shielding also must be kept in the storage
during the exchange
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Target station
Cross-sectional view
Target station top view
storage of radioactive materials
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Residual dose of the Target/Horn
Residual dose of 3cmF x 90cm Carbon Graphite
target (in a Al container) and 1st magnetic horn
is calculated.
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50GeV 0.75MW proton
Target Target Horn
(1)(Sv/h) (2)(Sv/h) (1)(Sv/h)
1 day 16.9 18 18
1 month 11.6 12.3 3.9
1 year 0.148 0.16 2.8
5 year 8.3x10-10 8.9x10-10 ------
10 year ------ ------ 0.25
20 year ------ ------ 1.7x10-5
After 1 year operation
(1)NMTC/JAM(nmtclib95)
DCHAIN-SP
QAD-CGGP2
(2)Hadron fluence(MARS)
cross section(9mb)
7Be life
Horn must be kept in the storage for more than 10
years.
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Residual dose of the Shielding
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Residual dose of the shielding calculated by MARS
(1 year operation, 1 day cooling, 0.75MW)
Use of Al surface reduce the radiation about one
order of magnitude.
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Further calculation is needed after the
scenario is fixed.
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Requirement for the boundary during the
maintenance
MCNP is used. g-ray source are
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defined on the Al tunnel surface.
0.75MW 1-year operation, 1-day cooling
0.25mSv/h
0.4Sv/h
Radiation from residual dose in the tunnel is
satisfactory small.
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Calculation of Decay Volume Shielding
As the target station, virtual cylindrical
geometry is used in the MARS calculation.
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5.05.9m of concrete and additional 6m of soil
are needed to satisfy concrete and soil surface
condition
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Radiation behind the Beam Dump
At the muon pit, muons from p?nm must be measured
with energy threshold of 25GeV to study neutrino
property.
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Copper 1.5m Iron 1.5m concrete 0.5m satisfy
this requirement. The threshold for the muons is
Eth4.5GeV
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The residual dose in the muon pit(30days beam, 1
day cooling, 0.75MW) is 0.2mSv/h.
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We can enter the muon pit after the beam stop.
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Management of Cooling Water
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Regulation Radioactive water can be exhausted
to outside (ocean) if radioactivity is less than
15Bq/cc.
Radioactive primary cooling water is circulated
only in the underground control area during the
beam period.
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Target/Horn cooling
Heat exchange
Primary cooling water system
Secondary cooling water system
Third cooling water system
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Disposal Scenario of Radioactive Water
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After 20days operation, the all radioactive water
is transferred to a DP tank in the disposal
system. The cooling system for the decay volume
is used for this purpose (to save money).
They are mixed with fresh water in the dilution
tank.
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Primary cooling water from Target/Horn
Primary cooling water from Beam Dump
DP tank
Fresh water
After measurement of radioactivity in the
dilution tank, the water can be disposed. It
takes 1 or 2 days for the measurement.
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Dilution tank
Disposal line
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Summary of cooling water and their
radio-activation
0.75MW , 20days operation
component Water in the beam-line (liter) Water in the system (liter) Neutron fluence (/cm2/p) Total 3H (GBq) 15Bq/cc equiv. Vol. (m3)
Norm. Cond. Mag. ------ 30000 ------ 0.07 5
Target 1 100 8x10-3 2.3 150
Horn x 3 ------ 200x3 ------ 1.0x3 66x3
Target Station 55 ------ 4x10-5 0.63 42
Decay Volume 1100 ------ 1x10-5 3.3 220
Beam Dump 13 ------ 1x10-5 0.04 2.6
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We need a capacity of 600m3 to dispose all
together. If we make 60m3 dilution tank, we must
repeat the dilutions 10 times.
We must also consider a possibility to confine
the primary cooling water in the radiation
control area forever.
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Ventilation of Air and Helium
Regulation Radioactive gas (air/Helium) can be
ventilated to environment if radioactivity is
less than 5mBq/cc.
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Air in the low radioactivity area (e.g. surface
building) is always ventilated even during the
beam period.
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High radioactivity area (e.g. underground control
area) is closed in the beam period.
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After the beam stop, high radioactive air/Helium
must be mixed with fresh air and ventilated
gradually if the radioactivity exceed 5mBq/cc.
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Summary of Air/Helium and their radio-activation

0.75MW , 20days operation
sair30mb, sHe1.2mb, Ventilation 8000m3/h, lt
5mBq/cc
component volume (m3) Neutron fluence (/p/cm2) Radio-activation(Bq/cc) 5mBq/cc equiv. Vol. (m3) Ventilation Ventilation time(h)
Surface building 8000 1?10-19 4?10-14 8000 A 1
Service pit 230 5?10-12 2?10-6 230 B 0.03
U.g. machine room 330 5?10-12 2?10-6 330 B 0.04
radioactive storage 780 5?10-12 2?10-6 780 B 0.1
Iron cooling (out)? 38 1?10-10 4?10-5 38 B 0.005
Iron cooling (cent)? 33 1?10-8 4?10-3 33 B? 0.004
Iron cooling (in)? 28 2?10-5 8 44800 C 5.6
TS Helium (air) 135 2?10-4 3.2 (80) 86400 C 10.8(270)
DV Helium (air) 1600 5?10-5 0.8 (20) 256000 C 32(800)
A Ventilate during beam period B Ventilate
directly after beam stop
C Ventilate by mixing with fresh air after beam
stop