Information Notice No. 81-26: Compilation of Health Physics Related Information Items
SSINS No.: 6835
Accession No.:
8107230026
IN 81-26
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
August 28, 1981
Information Notice No. 81-26: COMPILATION OF HEALTH PHYSICS RELATED
INFORMATION ITEMS
Part 1: Use of Recirculating-Mode (Closed-Circuit) Self-Contained
Breathing Apparatus (Rebreathers)
Part 2: Use of the Chemical "DOP"
Part 3: Placement of Personnel Monitoring Devices for External Radiation
Exposure
Part 4: Personnel Entry into Inerted Containment
Part 5: Evaluation of Instrument Characteristics When Using Portable
Radiation Survey Instruments
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IN 81-26, Part 1
August 28, 1981
Page 1 of 3
Information Notice No. 81-26, PART 1: USE OF RECIRCULATING-MODE
(CLOSED- CIRCUIT)
SELF-CONTAINED
BREATHING APPARATUS
(REBREATHERS)
Description of Circumstances:
This notice updates information in Information Notice No. 80-19 issued on
May 6, 1980 that informed licensees of a National Institute for Occupational
Safety and Health (NIOSH) "stop-sales-and-recall" order of the BioPak-60P
(60P) recirculating-mode (closed-circuit) self-contained breathing apparatus
(rebreathers) identified as SCBA-R. It also provides updated guidelines for
the use of SCBA-R.
NIOSH rescinded its stop-sales-and-recall order (NIOSH Users Notice of July
11, 1980) after the original problem was satisfactorily resolved. The Los
Alamos National Laboratory (LANL) has retested the equipment, as approved
since the rescinding of the recall, to assure that recommendations on use
are based on the performance of devices tested and certified by NIOSH.
Discussion:
Current regulatory guidance (Regulatory Guide 8.15, "Acceptable Practices
for Respiratory Protection") recognizes only a "demand" mode of operation
for rebreathers (i.e., a mode in which there is some negative pressure in
the facepiece during at least part of the breathing cycle). The protection
factor permitted for such devices with full facepieces is 50.
The recently developed 60P rebreather operates in the positive-pressure mode
(i.e., pressure in the facepiece remains positive throughout the breathing
cycle). This device has been issued NIOSH test and certification number
TC-13F-85. Therefore, under the provisions of 10 CFR 20.103 and Regulatory
Guide 8.15, Section C, NRC licensees may make allowances for the use of the
60P in estimating exposures of individuals to airborne radioactive
materials. However, the NIOSH certification tests do not differentiate this
new class of positive-pressure rebreathers from the demand-mode rebreathers,
and no quantitative information on efficacy (protection factors) is
provided.
Guidance:
The Los Alamos National Laboratory has tested the new devices as part of its
ongoing program for NRC. LANL has developed sufficient information for NRC
to provide authorization for the use of these rebreathers with an assigned
protection factor of 5,000. In addition to the existing regulatory position
presented in Regulatory Guide 8.15, the following guidance pertains to the
use of positive-pressure rebreathers and should be followed by licensees who
use the rebreathers. Some of the discussion deals specifically with the 60P
rebreather that, at present, is the only available NIOSH
tested-and-certified device of this type.
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IN 81-26, Part 1
August 28, 1981
Page 2 of 3
1. For work in which very high protection factors are required, the
positive-pressure (pressure-demand), open-circuit, self-contained
breathing apparatus (SCBA) is still the apparatus of choice, unless the
advantage of increased working time provided by a positive-pressure
rebreather is necessary. The nominal "30-minute" open-circuit SCBA will
provide air for only 15 or 20 minutes under fairly heavy working
conditions. A recent report presents data indicating that, under very
heavy working rates, standard air cylinders can be exhausted in as
little as 10 minutes (L. G. Myhre, et al., "Physiological Limits of
Firefighters," ESL-TR-79-06, Final Report, Air Force School of
Aerospace Medicine, October 1977-January 1979). The 60P, which was
tested at LANL under moderate working rates, provided at least a full
60 minutes of service; it also weighs less than most open-circuit SCBA.
However, all rebreathers have an inherent problem; should contaminants
enter the system, such as through a temporary facepiece leak, they
would generally circulate through the breathing bags and be breathed
repeatedly. Open-circuit devices, on the other hand, clear themselves
of contaminants much more quickly because breath is exhaled to
atmosphere and clean air is supplied with each inhalation.
2. Perceptible outward leakage of air from SCBA-R at any time is
unacceptable because service life will be reduced to only a few
minutes. The rebreather makeup air supply comes from a small bottle of
oxygen that will be quickly exhausted if the facial seal of the mask is
not maintained. Wearers of positive-pressure SCBA-R have to be trained
to immediately leave the area where the respirator is required if such
outward leakage is detected.
3. It is important that each person who is to use the rebreather be
quantitatively fit tested. To the extent that the test hood or chamber
will allow, many different body and head movements should be included
in these tests to simulate actual work movements while protection
factors are measured. A satisfactory fit is provided when a protection
factor of at least 5,000 is achieved (no more than 0.02%. leakage).
These devices, when well-fitted, can provide protection factors of
20,000 or greater. Therefore, a factor of less than 5,000 indicates an
unacceptably poor fit for the situations in which such equipment is
designed for use. There is also the practical consideration that many
licensees use quantitative fit test equipment (e.g., with sodium
chloride aerosol) that cannot generally measure protection factors much
greater than 5,000.
The mask supplied with the 60P is manufactured by AGA (Swedish Company)
and comes in only one size. It is a relatively wide mask that will stay
well sealed to the face for good protection for those users who have
wider faces. People with narrow faces, particularly those with narrow
and short faces, might be unable to achieve a satisfactory fit (i.e.,
a fit with a protection factor of at least 5,000).
4. Special training is essential for people who will use rebreathers. The
operation of rebreathers is very different from that of open-circuit
SCBA with which many workers are familiar. Training should include, in
addition to the usual information on the construction and operation of
the unit,
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IN 81-26, Part 1
August 28, 1981
Page 3 of 3
hands-on refilling of the carbon-dioxide-removing sorbent and
replacement of the oxygen supply bottle (even though maintenance will
not be performed by the wearer). Training should also include
instruction in the function of the anti-anoxia valve (the wearer will
experience difficulty in exhaling as a warning that the oxygen supply
is shut off). Trainees should wear the unit while exercising (e.g.,
jogging, calisthenics, simulated work movements) to learn of any
restrictions experienced in breathing or in movement. They should use
the unit to end-of-service air supply to become familiar with the
behavior of the unit as it runs down and to recognize the
end-of-service whistle that sounds for only a brief time. Training
should be sufficiently extensive for wearers to be thoroughly familiar
with and confident in the use of the apparatus.
5. An anti-fogging solution should be applied to the facepiece lens before
each use since there is much more fogging in rebreathers than in
open-circuit equipment. Some of the first samples of anti-fogging
solution supplied to LANL by Biomarine Industries were defective.
Licensees who have purchased this solution should check with the
manufacturer about the need for replacement chemicals. Part of the
training should prepare wearers to expect more fogging than they have
experienced with open-circuit apparatus.
6. The manufacturer of the BioPak-60P has alerted purchasers of the
equipment to attach a special accessory hood (the "BioShield") to the
60P when it is used in fire fighting. The hood consists of a flexible
"Beta Glass" covering that stretch-fits around the visor and covers the
head, facemask, and hoses to the wearer's shoulders. The purpose of the
hood is to keep flames or falling embers from igniting combustible
materials (such as hair) that might be close to a leak of concentrated
oxygen from the equipment (e.g., out of the facepiece). NIOSH
certification permits the use of this accessory hood. Licensees who use
the 60P for firefighting, or near open flames or falling sparks or
embers, should also use this special fire resistant accessory hood to
prevent serious or fatal burns that could result from an oxygen-fed
fire.
This Information Notice No. is provided to notify licensees of the authorized
use of the BioPak-60P and the interim regulatory positions. When Regulatory
Guide 8.15, "Acceptable Programs for Respiratory Protection," is revised,
the revision will reflect NIOSH certification and LANL testing of
rebreathers. In the interim, NRC Inspectors will use. the specific guidance
provided above in addition to the regulatory positions given in Regulatory
Guide 8.15 for evaluating the acceptability of licensee respiratory
protection programs.
No written response to this information notice is required. If you need
additional information with regard to this matter, please contact the
appropriate NRC regional office.
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IN 81-26, Part 2
August 28, 1981
Page 1 of 3
Information Notice No. 81-26, PART 2: USE OF THE CHEMICAL "DOP"
Introduction:
This information notice contains preliminary information dealing with the
potential toxicity of the chemical di-sec, octyl phthalate (DOP) as shown by
animal testing conducted by the National Cancer Institute/National
Toxicology Program (NTP). Further guidance will be issued when more
definitive information is developed about DOP and its applications and use.
Background:
DOP, also called di(2-ethylhexyl) phthalate (DEHP), is used in many
facilities, including those of some NRC licensees, for quality assurance
testing and in-place testing of high-efficiency particulate air (HEPA)
filters and for recommended quantitative facepiece fit testing of
respirators.
DOP is also a plasticizer commonly added to give flexibility to polymers
(e.g., polyvinyl chloride). As such, it is used in natural and synthetic
rubbers, lacquers, cellulose compounds, and as a pump fluid for
oil-diffusion pumps. Because it is produced and used in very large amounts
(almost 400 million pounds in the United States in 1977), exposure of the
general population to products containing DOP is widespread. The U.S. Food
and Drug Administration (FDA) approved DOP for use in polymers in
food-contact items, and it is used in vinyl tubing to transfer blood,
intravenous fluids, and milk. DOP has been found in blood stored in vinyl
bags and transferred through vinyl tubing (up to 66 mg/l of blood and 250
mg/l in bagged plasma). It has been found in the tissues of patients
transfused with blood or blood products stored in flexible polyvinyl
chloride containers. DOP has also been found in neo-natal tissues after
umbilical catheterization. Children who are given multiple transfusions of
blood to treat serious blood diseases might, in a year, receive as much as
1500 mg (about 28 mg/kg) of DOP.
Hazard Assessments:
DOP has, until recently, been considered to be a substance of low toxicity
by all routes of intake. The recommended time-weighted average threshold
limit value (TLV) for the work environment that is adopted by the
Occupational Safety and Health Administration (OSHA) is 5 mg/m3 in air--the
same as that for certain nuisance dusts.
However, the National Cancer Institute/National Toxicology Program recently
conducted carcinogenesis bioassay tests on DOP/DEHP. One strain of mouse and
one strain of rat in a lifetime feeding study were fed relatively large
amounts of DOP (3,000 to 12,000 ppm) in dosed feed. No inhalation study was
performed.
A draft NTP report of this study, which has been reviewed and approved with
slight changes by the NTP Peer-Review Panel of Experts, finds that DOP is
carcinogenic in B6C3Fl mice and in F344 rats (hepatocellular carcinomas in
mice and hepatocellular carcinomas and neoplastic nodules in female rats).
The report makes no determination of risk to humans.
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IN 81-26
August 28, 1981
Page 2 of 3
Current Considerations:
The National Institute for Occupational Safety and Health (NIOSH) has not
yet issued final revised new recommendations on the suitability of DOP for
various uses. However, on April 30, 1981, NIOSH issued for comment a draft
special report on DEHP toxicity. The draft report recommends corn oil as the
best alternative from a toxicological viewpoint, for the time being, as a
substitute aerosol for quantitative facepiece fitting of respirators. Final
recommendations are expected within a few months.
The Los Alamos National Laboratory (LANL) is investigating potential
substitutes for DOP (in quantitative fit testing) for both NRC and the
Department of Energy (DOE). LANL has successfully used di-2 (ethylhexyl)
sebacate (DEHS, "Octoil-S") as a substitute test agent that seems to be of
acceptably low toxicity according, to current data. The draft NIOSH report
also examines the suitability of DEHS as a substitute for DOP in generating
quantitative fit test aerosols. The report does not rule out such use of
DEHS at this time, but it indicates that more toxicity tests are needed
before NIOSH can make a more definitive recommendation on such use of DEHS.
Manufacturers of quantitative fit test equipment have recommended the use of
corn oil as an interim substitute test agent for DOP. A satisfactory test
aerosol can be generated from corn oil for making the measurements. There
may be some disadvantages, however, in odor (described as that of french
fries or popcorn) from oxidation of the oil, potential for mold growth on
test chamber exit-air filters, and housekeeping problems from the need for
more frequent and more difficult cleaning.
Guidance:
A forthcoming final NTP report may find that DOP/DEHP is a weak carcinogen
in two strains of mice and rats as indicated by feeding studies. DOP is
present in many products in common use, and human exposures to it are
widespread. NIOSH and OSHA have not yet had time to fully evaluate and make
recommendations on the health significance of exposures to and uses of DOP.
Until such information is available, the following interim guidance is
suggested for licensees:
1. For quantitative respirator fit testing, even though human exposures
are very small during these tests, it would be prudent, at least for
now, to discontinue the use of DOP and to substitute an available, less
potentially hazardous test agent for these tests. Corn oil, as
recommended by the test equipment manufacturers, is acceptable for this
use. Licensees should check with manufacturers for detailed
instructions on the use of corn oil and on how to avoid or minimize
potential problems with odor, mold growth, and cleaning. Di-2
(ethylhexyl) sebacate ("Octoil-S") may also be used if manufacturers
deem it compatible with the operation of their equipment.
2. For quality assurance or in-place testing of HEPA filters, DOP may be
used where required. However, emissions of DOP from generating and test
equipment should be controlled by containment and ventilation to avoid
unnecessary exposures of personnel. Exposures of personnel to DOP
should be individually assessed and minimized by well-planned work
practices. Respiratory protective equipment should be used if
necessary.
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IN 81-26, Part 2
August 28, 1981
Page 3 of 3
Several different agencies are continuing to clarify and resolve the
questions that arise with respect to the use of DOP. Licensees will be
further informed as more definite information is developed about DOP,
suitable substitutes, or recommendations on permissible applications and
use.
No written response to this information notice is required. If you have any
questions regarding this matter, please contact the appropriate NRC Regional
Office.
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IN 81-26, Part 3
August 28, 1981
Page 1 of 2
Information Notice No. 81-26, PART 3: PLACEMENT OF PERSONNEL
MONITORING DEVICES FOR EXTERNAL
RADIATION EXPOSURE
Description of Circumstances:
A recent inspection at a nuclear power plant revealed a situation in which
inappropriate placement of personnel monitoring devices resulted in under-
estimating the radiation dose received by the workers. In this case, the
heads and lenses of the workers' eyes were exposed to about 50% more
radiation than was measured by their chest-worn film badges and self-reading
pocket dosimeters. Such a nonuniform radiation field resulted during repair
work in a steam generator when the principal source of radiation came from
overhead. Conservative re-evaluation by the licensee of the dose received by
these individuals revealed that sixty-six workers may have exceeded their 3
rem per calendar quarter exposure limit specified in 10 CFR 20.101.
On a regular basis, NRC inspectors observe other situations where sufficient
attention has not been given to the placement of personnel dosimeters. Many
of these involve situations where significant extremity (hand) exposure
occurs and extremity dosimeters are not supplied to workers by the licensee.
In many cases, the licensee has not made the necessary surveys and/or
calculations to adequately evaluate the need to supply extremity dosimeters
to the workers. In other cases, the evaluations may have been conducted, but
no evaluation records are available.
Discussion:
It is fairly standard practice to wear personnel dosimeters on the trunk,
most frequently at the chest or waist position. This is acceptable practice
when workers are exposed to relatively uniform fields of radiation. However,
it is important to evaluate all nonstandard and unusual situations,
particularly where high dose rates are possible, to determine if trunk-worn
dosimeters are appropriate. In the majority of the cases, the dose limit of
interest is the one that applies to the whole body, head and trunk, active
blood-forming organs, lenses of eyes, and gonads. Since the same limit
applies to all of these body locations, the potential dose to each should be
considered. The objective should be to place the dosimeter in a position
where it will measure the highest dose to the areas of interest.
Therefore, if the principal source of radiation is overhead, the dosimeter
should probably be placed on the head. If the principal source of radiation
is from underfoot, the appropriate location for the dosimeter might be on
the lower leg just above the ankle, since long bones of the lower leg
contain active blood-forming marrow. If a worker is sitting on or straddling
the source of radiation, the dosimeter should be positioned to record the
radiation dose to the gonads. If the source of radiation is predominantly
behind the workers, the dosimeter should be worn on the back rather than on
the front of the body. To be explicit, the dosimeter should be worn at the
location of highest entry dose.
The other situation that occurs regularly is significantly higher exposure
to the hands, forearms, feet, or ankles. These situations occur most
frequently during direct handling or manipulation of radioactive items or
while working
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IN 81-26, Part 3
August 28, 1981
Page 2 of 2
from behind a partial shield. In many of these cases, NRC regulations would
require wearing dosimeters to record what might be termed the "whole body
dose" and dosimeters to record the dose to the extremities.
NRC Regulation 10 CFR 20.202 requires that an appropriate personnel
monitoring device be worn if an individual receives or is likely to receive
a dose in a calendar quarter in excess of 25% of the values specified in
paragraph (a) of 10 CFR 20.101. Thus, a "whole body badge" is required if
300 mrem per quarter is likely to be received by those portions of the body
with a limit of 1.25 rem per quarter. In addition, an extremity badge is
required if an extremity is likely to receive about 4.7 rem in a quarter.
Dosimetry for the only other limit, skin of whole body, is normally
accommodated by the beta capability of most personnel dosimeters.
All of the discussions above apply to situations in which the NRC
regulations require that dosimeters be worn by radiation workers. There are
many cases hen an employer may choose to supply dosimeters to workers above
and beyond the NRC requirements. This may be done for administrative,
information gathering, or other purposes. In some special situations, a
worker may be seen wearing several dosimeters. Such conservative safety
practices are encouraged.
Some discussion of requirements for radiation surveys and evaluations may be
in order. Because 10 CFR Part 20 requires each licensee to supply personnel
dosimeters to workers under certain conditions, there is the companion
requirement that the licensee make such surveys and evaluations necessary to
comply with that requirement. For example, if significant hand exposure is
likely to occur and a licensee chooses not to supply extremity dosimeters,
the potential dose to the hands must have been evaluated by instrument
surveys, calculations, or by other means to support the position that
extremity monitoring is not required. Records of such surveys and
evaluations must be maintained for inspection.
Guidance:
No written response to this notice is required. Licensees should review
their radiation survey and evaluation practices to ensure personnel
monioring requirements are met. Special attention should be given to
nonuniform radiation fields.
If you require additional information regarding this subject, please contact
the appropriate NRC Regional Office.
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IN 81-26, Part 4
August 28, 1981
Page 1 of 3
Information Notice No. 81-26, PART 4: PERSONNEL ENTRY INTO INERTED
CONTAINMENT
Introduction:
The information provided below deals with personnel safety issues that are
outside the scope of the NRC's nuclear safety requirements; as such no
action or response to this information notice is required. However, this
information notice provides useful information that will be helpful to
licensees in their efforts to maintain safe working conditions for their
employees.
Description of Circumstances:
On February 24, 1981, a boiling water reactor (BWR) licensee dispatched
three workers, who were fitted with self-contained breathing apparatus
(SCBA), into the primary containment (drywell) with the reactor at 30% power
and the drywell fully nitrogen-inerted to approximately 3% oxygen by volume.
The purpose of this drywell entry was to determine the source of
unidentified, primary system leakage into the drywell.
An inerted drywell constitutes an atmosphere immediately dangerous to life
and health (IDLH). Personnel safety provisions for the February 24 entry
included verbally restricting the areas where the personnel should travel in
the containment; providing two other persons with SCBA equipment on standby
outside the containment airlock for rescue, if necessary; and preparing for
ventilating the containment if a problem arose. The entry lasted 7 minutes
and the plant page system was used occasionally to verify the status of the
work party. Upon completion of the activity, the work party left the
containment with no reported problems. Licensee management reportedly
authorized the entry for the purpose of maintaining the plant at power,
rather than shutting down.
Discussion:
Had an individual's air supply failed while in the inerted drywell, the
planned deinerting in the event of a problem would not have prevented severe
personnel injury. Unprotected exposure to an atmosphere containing less than
6% oxygen by volume causes spasmodic breathing, convulsive movements, and
death in minutes. In atmosphere with oxygen content in the 8-12% by volume
range, unconsciousness can be immediate and without warning upon loss of air
supply (SCBA failure). Title 29, Code of Federal Regulations, Part 1910.34
provides certain regulatory requirements for the safe use of respirators in
dangerous atmospheres. It states, in part, "Communications (visual, voice or
signal line) shall be maintained between both or all individuals
present...," e.g., for this situation the working party in the drywell and
the rescue party outside the containment airlock. Given the logistics of the
situation and available communications equipment, the use of signal line or
voice communications was physically impossible. The licensee used the plant
pager system intermittently, and thus communications were not maintained on
a continual basis. Discussion with the licensee management revealed a lack
of awareness of the above-cited Title 29 requirement.
Other airborne-toxic/oxygen-deficient are as can exist at nuclear power
plants. Some examples include unventilated tanks or voids; inerted primary
components
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IN 81-26, Part 4
August 28, 1981
Page 2 of 3
such as steam generators or portions of primary loop piping; areas affected
by oxygen displacement fire suppression systems; confined spaces affected by
decaying marine growth, such as circulating water cooling systems; and areas
affected by leakage of chlorination systems or accidental mixing of caustic
and acid chemicals for makeup water treatment.
Subatmospheric containments can constitute oxygen-deficient areas, to
varying degrees, depending on the containment air pressure. At sea level,
for example, if the containment air pressure is 11.1 lb/in.2, then the
partial pressure of oxygen is approximately 120 mm of mercury; 30 CFR 11
defines an oxygen-deficient atmosphere as "...an atmosphere which contains
an oxygen partial pressure of less than 148 millimeters of mercury (19.5
percent by volume at sea level).
Another potential nonradiological hazard can exist for personnel making BWR
drywell entries. In some earlier designed plants, the primary safety valves
discharge directly to the drywell atmosphere. In the event of safety valve
activation, personnel could be severely injured or killed.
Guidance:
IDLH areas, such as an inerted BWR drywell, should not be entered. In fully
inerted areas, assuming SCBA failure, physical incapacitation occurs in
seconds and death occurs in minutes. If entry into inerted areas is required
under certain extreme emergency conditions and timely deinerting is not
possible, then carefully planned and controlled personnel entries can be
accomplished.
Even after purging and ventilating, a deinerted area can present a personnel
hazard. Pockets of the inerting gas can remain in localized low-lying areas
of the space. Before the deinerted area is opened for unrestricted worker
access, a thorough sampling inspection should be performed by personnel
equipped with SCBA.
Licensees should establish and maintain a nonradiological airborne hazards
control program. Basic elements of such a safety program should include the
following:
1. Identification of potential hazard areas
2. Quantification of the hazard potential
3. Procedural controls to implement safe work practices commensurate with
identified hazards
4. Worker training program
Such a nonradiological hazards control program could be an extension of the
licensee's respiratory protection program established to satisfy the
requirements of 10 CFR 20.103. NUREG-0041, "Manual of Respiratory Protection
Against Airborne Radioactive Materials," contains a summary of the OSHA
regulations in the nonradiological airborne hazards area (Chapter 3), and
provides a discussion of the evaluation and classification of respiratory
hazards (Chapter 4). Another useful reference document for improving worker
safety in nonradiological hazards areas is the DHEW (NIOSH) Publication No.
80-106, "Criteria for a Recommended
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IN 81-26, Part 4
August 28, 1981
Page 3 of 3
Standard...Working in Confined Spaces," December, 1979. This document is
available for purchase from the Superintendent of Documents, U.S. Government
Printing Office, Washington, DC 20402.
As discussed above, no specific actions or reports are required. If you have
any questions regarding this matter, please contact the appropriate NRC
Regional Office.
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IN 81-26, Part 5
August 28, 1981
Page 1 of 2
Information Notice No. 81-26, PART 5: EVALUATION OF INSTRUMENT
CHARACTERISTICS WHEN USING
PORTABLE RADIATION SURVEY
INSTRUMENTS
Description of Circumstances:
The Barnwell, South Carolina, radioactive waste burial site recently
received a shipment of radioactive waste that exceeded the radiation levels
specified by the U.S. Department of Transportation (DOT). The power reactor
licensee responsible for the shipment concluded that the error resulted from
the use of a portable radiation survey instrument in an orientation other
than that for which it was designed. ANSI N323-1978, "Radiation Protection
Instrumentation Test and Calibration," defines geotropism as a change in
instrument response with a change in instrument orientation as a result of
gravitational effects. ANSI N323-1978 discusses this phenomenon as well as
other nonradiological and radiological characteristics that should be
considered in the routine calibration and use of portable radiation survey
instruments.
Strictly speaking, geotropism is the result of gravitational forces on the
instrument. Almost invariably, this results from the effects of gravity on
the moving parts of conventional meter movements. For example, if an
instrument is calibrated in an upright orientation, a change in response may
be experienced if the instrument is used on its side with the earth's
gravity assisting (or resisting) the movement of the meter needle or other
meter movement parts. Additional geotropic effects can also be introduced if
instruments are not zeroed in the orientation in which the measurement will
be made. Geotropic effects are normally not present in those instruments
with digital readouts, since there are no moving meter parts.
Another instrument characteristic that is influenced by orientation is
termed "angular dependence." This effect may be observed when a change of
instrument response is noted or when there is a change in the direction from
which the radiation enters the detector. It is easy to visualize this effect
in an instrument with the detector mounted internally but on one side of the
instrument case. Thus, a measurement made with the side of the instrument
where the detector is located closest to the source may be considerably
higher than if the instrument is oriented so the radiation enters from the
side farthest from the detector. Some of this effect results from the
distance (geometry) effect and some may result from other parts of the
instrument between the source and the detector (shielding effect). Even
greater shielding effect is observed on most instruments if the radiation
enters from the back. Angular dependence may also be observed in instruments
with cylindrical detectors, either ionization or GM type. That is, a
different response may be obtained when the long axis of the detector is
pointed at the source than when it is oriented at right angles to the
source.
Guidance:
Improper orientation of radiation survey instruments during calibration or
use can cause errors in radiation measurements. All NRC licensees should
verify that personnel calibrating or using radiation survey instruments are
aware of this phenomenon and that controls are established to ensure that
instruments are properly oriented during calibration and use.
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IN 81-26, Part 5
August 28, 1981
Page 1 of 2
No written response to this information notice is required. If you require
additional information regarding this matter, contact the appropriate NRC
Regional Office.
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