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11321311
125 14 LE
MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS – 1963
APR 27 190$
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AN ACCELERATOR RADIATION PROTECTION SYSTEM
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ORNL.P-1145
G. F. Wells and W. E. Lingar
Oak Ridge National Laboratory
Oak Ridge, Tennessee
CONF. 650306-56
Accelerator induced radiation presents a
hazard to personnel that is generally controlled
by adequate shielding on the accelerator and
experimental areas and by removal of the charged
particle beam from an area when personnel must
have access to it. In the past, radiation de-
tectors and warning devices (flashing lights,
buzzers, etc.) have been used to indicate areas
of danger, and prudent personnel have success-
fiuly worked with accelerators without harm.
These procedures still form the first line of
protection against excessive exposure to radiation
at ORNI. High Voltage Accelerator laboratory. How-
ever, a second line of defense involving automatic
ARENI
B
AROME SCHON.
THE PER LA PROVED. PROZEDURES
PATENT GORE OBTAINED: RELEASE TU
to the Tandem Van de Graaff facilities in consi-
deration of the enlarged number of both experimen-
tal and servicing personnel using the facility.
The system permits time limited access to areas
where radiation is present, but tends to prevent
personnel receiving excessive exposure by re-
quiring that radiation producing beams be re-
moved from the area when a specified integrated
dose of gamma and neutron radiation has been
monitored.
System Description
This system provides a delayed automatic
shutdown of the accelerator beginning when a door
to a hazardous area is opened. The delay time is
inversely proportional to the radiation level in
that area except in a limiting case in which
accelerator shutdown becomes instantaneous upon
opening the door. Taus, limited monitored access
to reasonably low-level radiation areas may be
had without interruption of an experiment in
progress.
The components of the system are as shown in
Fig. 1. Ionization chambers were chosen as the
radiation detectors for two reasons; experience in

reactor control applications has shown them to be
far more reliable than almost any other type of
sensing element, and, unlike a counter, it is im-
possible to "jam" a chamber at high radiation
levels. The chambers used in this case have
yolumes of one liter; the filling is 76 cm Hg
JOBF, (96% 108. enrichment) plus 76 cm Hg argon.
A thin outer coating of ca and a thick jacket of
polyethylene are used to balance the response of
the assembly so that neutrons and y rays of equal
biological dose rates produce equal currents in
the chamber. The current in the chamber is a
fairly accurate indicator of the total biological
hazard. The chambers in each area are placed .
approximately 3 meters from the source of radia.
tion. The radiation field at one-half this dis-
tance from the source (4 times the field at the
chamber) is used as a basis for determining the
amount of accumulated dose to cause accelerator .
shutdown. The maximum allowable integrated dose
for an 8-hour period is 0.5 rem at this distance: 1
Thus, a radiation level of 0.125 rem at the.
chamber for 1 hour in an insecure area would cause
accelerator shutdown. ..
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The ionization chamber current is converted
by an electrometer amplifier to metering signals
which drive "allowable entry time" meters at
appropriate doors and duplicate meters for each
area at the main control console. A reading of
60 min. on the meter face corresponds to a radia-
tion level of 0.125 rem at the chamber. The full
scale meter reading of 6 min, corresponds to 1.25
rem and would cause instantaneous accelerator
shutdown if the area door were opened.
ALTAVA
The amplifier outputs are also connected to
& signal comparator circuit which selects the
maximum amplitude signal and feeds it to an in-
tegrator. The integrator produces an output
pulse-rate proportional to input voltage and
drives an electro-mechanical register. The
register has a preset number in it corresponding
to the permissable integrated dose. Since the
• integrator produces 100 counts per minute at a
radiation level of 0.125 rem at the ion chamber,
the preset register number is 6000 for accelerator
shut-down to occur in 1 hour. Every 8 hours
the register is reset by a timer whether it has
counted down or not, allowing another 8-hour in-
tegrated dose to be accumulated. It is to be
noted that this is an accumulative system, in-
tegrating counts produced by each separate entry
even though by different personnel in different
&re&s,
In the event the radiation level in a se-
cured zone is high enough to limit entry time to
< 6 min., the integrator count-down trip procedure
is superceded by an instantaneous accelerator trip
when a door to that zone is opened. This is per- :
formed by a preset contact meter relay in an
electrometer amplifier at the main console.
A procedural arrangement built into the
system calls for personnel guarantee that a
hazard area is clear. Door interlocks are so
arranged that not only must all doors to an area
be closed but a "secure" button outside that area
must be pressed to disconnect the amplifier output
signal from the integrator. When both conditions
are met a green "secure" light comes on at the
main console and the operator understands that a
certification has been made that no one is in the
area.
As to operating procedure, if for any reason
the accelerator is tripped by radiation integration
two things must happen. First, an investigation
would be made and new procedures enforced to prevent
& recurrence. Second, for the remainder of the
8-hour period until the integrator reseis itself
the accelerator may be operated only with all
zones "secure."
The details of this system are described by
the following ORNL drawings which are available.
on request to educational institutions and other
government research laboratories.
...-.--- -
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Ionization chamber -- Q-2289-1 .
Electrometer amplifier -- Q-2338-5, Q-2336-6
Signal Interconnecting and Grounding
Relays -- Q-2338-4
Signal Comparator and Selector -- Q-2338-3
Preset Timer and Counter -- Q-2338-2
System Block Diagram -- Q-2338-1
...
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circe.
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Operational Experience
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This system has been in operation in the
ORNL Tandem Van de Graaff facility for more than
1 year. In no instance has the count down . ;
feature caused accelerator shutdown. Experimenters
have respected the system which allows them reason-'
able entry for adjustment and alignment of appar-
atus. Servicing personnel have respected the .
"secure" aspect of areas they need to enter and
· requested entry time from the operator when
.. necessary. Only 3 "incidents" have occurred
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in which personnel entirely unfamiliar with the
area have inadvertently opened a secure zone. In
two of these cases the beam was immediately re-
moved from the area by the operator and an in- i
vestigation made of the unauthorized entry. In
the remaining case, the area entered had an upper
limit of radiation (< 6 min. entry time). The
system automatically tripped the accelerator
shutdown-reley, thus preventing any exposure.
. .
...
Maintenance on the system has consisted
principally of replacement of the electrometer
tube in the ion chamber signal amplifier, This
is done when a monthly check of amplifiers by the
Health Physics Division indicates a weak response
to a radioactive source brought near the ion
chamber. The system has performed its intended
function with 100% reliability at reasonably
little maintenance effort.
!
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The most important feature of the system
has been that there has never been a temptation
to disable it in any way. No interlocks have
been by-passed and no detectors have been dis-
abled; the reason is that the system does not
interfere with entry except where entry is
obviously very unwise. The fact that all doors
are unlocked means that, in case of fire or other
non-radiation emergencies, immediate entry will
merely trip the accelerator while attention is
paid to the emergency itself.
Institucibidin
Reference
1. Research sponsored by the U.S. Atomic Energy
Commission under contract with the Union Carbide
Corporation,
4
A
RT
ORNL-DWG. 65-2281

METER NO.1
(Localıd Outsid, Door No.102)
METER PANEL
(in Control Roo.)
ION CHAMBER
SHIELD
So
Q-2209-133
ELECTROKE TER
AMPLIFIER No. 1
(in Uashelded
Targot Room)
81.023311:586)
METER No.2
(Located outside Door No.102)
To Door Operated Rolayı 8.00-2338-7,
Q-2338-8, Q-2338-9,0-233.-10, 0-2338-11,
0-2330-12.
ELECTROMETER
AMPLIFIER NO. 2
(In Uashielded
Torget Room)
ION CHAMIER
& SHIELD
SIGNAL
INTERCONNECTION
AHD
GROUNDING RELAYS
(in Control Room)
0-2338-4
METER
(Locotod Outside Door No.103)
ION CHAMBER
SHIELD
ELECTROMETER
AMPLIFIER
(in Shielded
Targot Room)
METER
(Located outside Door Na 1171
METER
(Located Outside Door No.104)
SIGNAL
COMPARATOR
AND
SELECTOR
sin Control Room)
0-2330-3
ELECTROMETER
AMPLIFIER NO. I
(In Low Moss
Torgot Room)
ION CHAMPER
SHIELD
!
METER
(Located Inside Door No. 117)
METER
(Located Outsid. Door No.104)
ION CHAMBER
& SHIELD
ELECTROMETER
AMPLIFIER No. 2
(in LOW MOIS
Targot Room)
RATE TRIP
SIONAL
METER
(Locutod Outside Door Na 100)
METER
(Locatod Outside Door No.llo)
ROY SON
LECTROCOUNT
INTEGRATOR
(in Control Room)
ION CHAMBER
O SHIELD
ELECTROMETER
AMPLIFIER NO. 2
(in Accelerator
Area Wast)
METER
(Located inside Door No. 116)
ION CHAMBER
I SHIELD
ELECTROMETER
AMPLIFIER
(in Accelerator
Aroo East)
N-
PRESET
TIMER
AND
COUNTER
(in Control Room)
Q-2336-2
To Accelerator
Trip Circuit
ION CHAMBER
I SHIELD
ELECTROMETER
AMPLIFIER
(in Control Room)
V
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Fig. I RADIATION PROTECTION SYSTEM BLOCK DIAGRAM
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ITAL
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ON
.EP.
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END
125
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E-
DATE FILMED
11/ 15 /65







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