Information Notice 1991-30, Inadequate Calibration of Thermoluminescent Dosimeters Utilized to Monitor Extremity Dose at Uranium Processing and Fabrication Facilities
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
April 23, 1991 NRC INFORMATION NOTICE NO. 91-30:
INADEQUATE CALIBRATION OF THERMOLUMINESCENT
DOSIMETERS UTILIZED TO MONITOR EXTREMITY
DOSE AT URANIUM PROCESSING AND FABRICATION
FACILITIES
Addressees
All fuel cycle licensees and other licensees routinely handling unshielded
uranium materials.
Purpose
This information notice is being provided to alert addressees to potential
problems resulting from inadequate calibration of thermoluminescent dosimetry
(TLD) utilized to monitor extremity dose.
It is expected that licensees
will review the information for applicability to their facilities, distribute it
to radiation safety personnel, and consider actions, as appropriate, to avoid
similar problems.
However, suggestions contained in this Information Notice do
not constitute new U.S. Nuclear Regulatory Commission (NRC) requirements;
therefore, no specific action or written response is required.
Description of Circumstances
During August-September 1990, an NRC licensee conducted evaluations of extremity
exposures to beta particles for selected personnel handling unshielded uranium
materials.
The evaluation included both extremity monitoring for workers
handling the materials and a determination of the dose rate from unshielded
uranium material (pellets). Monitoring was conducted using single chip TLDs
mounted in plastic finger rings.
Pellet dose rates were determined by exposing
TLDs to the unclad material for a known period.
TLDs were supplied and
subsequently processed by a vendor laboratory.
The licensee had verbally
discussed with the vendor that the monitoring with the finger ring TLOs was
conducted to determine employee beta extremity dose from the unshielded uranium
materials.
In addition, the licensee included instructions stating the type of
radioactive materials which were to be monitored with their purchase agreement
accompanying the TLDs to the processing vendor laboratory.
Based on vendor reports for TLDs affixed to uranium pellets for a set amount of
time, the licensee calculated dose rates of 38 and 40 mrem/hr through an absorber
thickness of 7 milligrams per square centimeter (mg/cm2).
Initially, the
licensee assumed the pellet dose reports to be accurate and no additional
calculations were made to support the vendor measurements.
However, in response
to NRC inquiries, independent calculations were made which indicated that the
914706 Z;
'
A
W
-/
I
d
April 23, 1991 minimum dose rate from the pellet material exceeded the values derived from the
vendor reports by a factor of approximately 2.
During discussion of the dose measurements with the TLD vendor, the licensee was
informed that the TLDs were calibrated with a cesium-137 (Cs-1371 source.
The
vendor had a calibration factor for TLDs exposed to a slab of natural uranium
and noted that a correction factor was required to convert from a cesium-based
to uranium-based shallow (skin) dose.
Review of the licensee dose data indicated
that the appropriate correction factor was not applied to the original results
provided by the vendor. A beta-correction factor of approximately 2.0 was
required, and higher dose values were subsequently assigned to personnel handling
unclad uranium materials.
Subsequently, NRC contacted four other fuel fab'ication facilities regarding
their evaluations of extremity dose from depleted or low enriched unshielded
These facilities used single chip TLDs processed by vendor laboratories.
Among the facilities, three different vendors were represented in providing and
processing the TLDs.
During discussions with these vendors, it was determined
that a correction factor of approximately 2.0'should have been applied to the
reported results.
In all cases, this value had'not been applied to any of the
actual TLD measurements. As a result, extremity exposures had been underestimated
by a factor of approximately 2.
Discussion:
At fuel fabrication facilities, as well as at facilities handling natural'and
depleted uranium, selected operational processes potentially require extensive
handling of unshielded uranium materials by employees. Depending on the'facility
processes, dose rates to the skin of the extremity from unclad uranium materials
can increase significantly during operatibns. At fuel fabrication'facilities
following introduction of uranium hexafluoride (UF6) into the process, the major
contributor to the skin dose results from ingrowth of the beta-emitting metastable
protactinium-234 (Pa-234m) isotope.
Dose rates thrbugh'6-7 mg/cm2 absorbers of
approximately'200 millirem per hour (mreM/hr) for exposure to depleted, natural, or low-enriched unshielded uranium materials in equilibrium with short-lived
daughter isotopes have been reported (References 1-2).
It is the licensee's
responsibility to properly evaluate the potential dose to the skin of the
extremity to determine the need for extremity monitoring, and to verify that no
individual exceeds the exposure limits'specified in 10 CFR Part 20.
In using
TLD's for extremity monitoring,'licensees should verify that the appropriate
correction factor for the different TLD response between uranium and the
calibration source is used.
April 23, 1991 No specific action or written response is required by this information notice.
If you have questions about this matter, please contact the technical contacts
listed below or the appropriate regional office.
Rcha
E. Cunningha
Director
Division of Industrial and
Medical Nuclear Safety, NMSS
Office of Nuclear Material Safety
and Safeguards
Technical Contacts: George B. Kuzo, Region II
(404) 331-2560
John Potter, Region II
(404) 331-5571 Attachments:
1. References
2. List of Recently Issued NRC
Information Notices
3. List of Recently Issued NMSS
Information Notices
Attachment 1
April 23, 1991 REFERENCES
1. Coleman, R. L., C. G. Hudson, and P. A. Plato, 1983.
"Depth-dose Curves for
Sr-90 and Natural and Depleted Uranium in Mylar." Health Phys.
44(4):395-402.
2. U. S. Department of Health Education and Welfare (DHEW).
1970.
Radiological Health Handbook.
Public Health Service Publication, Rockville, Maryland.
Attachment 2
April 23, 1991 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
86-21, Supp. 2
91-29
91-28
91-27
Recognition of American
Society of Mechanical Engi- neers Accreditation Pro- gram for N Stamp Holders
Deficiencies Identified
During Electrical Distri- bution System Functional
Inspections
Cracking in Feedwater
System Piping
Incorrect Rotation of
Positive Displacement Pump
Pressurizer Safety Valve
Lift Setpoint Shift
Potential Nonconservative
Errors in the Working Format
Hansen-Roach Cross-Section
Set Provided with The Keno
and Scale Codes
Commercial-Grade Structural
Framing Components Supplied
As Nuclear Safety-Related
Equipment
04/12/91
All holders of OLs or CPs
for nuclear power reactors
and all recipients of
NUREG-0040, "Licensee Con- tractor and Vendor Inspection
Status Report" (White Book).
04/15/91
All holders of OLs or
CPs for nuclear power
reactors.
04/15/91
All holders of OLs or
CPs for pressurized water
reactors (PWRs).
04/10/91
All holders of OLs or
CPs for nuclear power
reactors.
04/10/91
All holders of OLs or
CPs for nuclear power
reactors.
04/02/91
All fuel cycle licensees
and other licensees, in- cluding all holders of
operating licenses for
nuclear power reactors, who use physics codes to
support criticality
safety in the use of
fissile material.
04/01/91
All holders of OLs or
CPs for nuclear power
reactors.
89-90,
Supp. 1
91-26
91-25 OL = Operating License
CP = Construction Permit
- Attachment 3
,
i Apria
1 f i1 Page 1 of I
LIST OF RECENTLY ISSUED
NMSS INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
91-26
91-23
91-16
Potential Nonconservative
Errors in the Working Format
Hansen-Roach Cross-Section
Set Provided with The Keno
and Scale Codes
Accidental Radiation Over- exposures to Personnel due
to Industrial Radiography
Accessory Equipment Malfunc- tions
Unmonitored Release Pathways
from Slightly Contaminated Re- cycle and Recirculation Water
Systems At A Fuel Facility
Recent Safety-Related Inci- dents at Large Irradiators
Management of Wastes Contam- inated with Radioactive
Materials ("Red Bag" Waste
and Ordinary Trash)
Brachytherapy Source Management
04/02/91
All fuel cycle licensees
and other licensees, in- cluding all holders of
operating licenses for
nuclear power reactors, who use physics codes to
support criticality
safety in the use of
fissile material.
03/26/91
All Nuclear Regulatory Cc
mission (NRC) licensees
authorized to use sealed
sources for industrial
radiography.
03/06/91
All fuel cycle facilities
03/05/91
All Nuclear Regulatory
Commission (NRC) licensee
authorized to possess anc
use sealed sources at
large irradiators.
01/07/91 All medical licensees.
91-14
91-03
91-02
01/07/91
All Nuclear Regulatory
Commission (NRC) medi- cal licensees author- ized to use byproduct
material for medical
purposes.
April 23, 1991 No specific action or written response is required by this information notice.
If you have questions about this matter, please contact the technical contacts
listed below or the appropriate regional office.
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety, NMSS
Office of Nuclear Material Safety
and Safeguards
Technical Contacts:
George B. Kuzo, Region II
(404) 331-2560
John Potter, Region II
(404) 331-5571 Attachments:
1. References
2.
List of Recently Issued NRC
Information Notices
3. List of Recently Issued NMSS
Information Notices
- See previous concurrence
OFC :IMOB*
- IMOB* :IMSB*
- IMNS
- IMN n
NAME :CTrottier/ll:JHickey:CHaughney :GS:R(
om :REC
ingha fj1
~~~~~~~~~~~~~--
t--
~~~~~
DATE :2/14/91
- 2/14/91: 2/14/91
- 4/15/91 :4/l /91
OFFICIAL RECORD COPY
IN 91- April
, 1991 that the appropriate correction factor was not applied to the original results
provided by the vendor. A beta-correction factor of approximately 2.0 was
required, and higher dose values were subsequently assigned to personnel handling
unclad uranium materials.
Subsequently, NRC contacted four other fuel fabrication facilities regarding
their evaluations of extremity dose from depleted or low enriched unshielded
These facilities used single chip TLDs processed by vendor laboratories.
Among the facilities, three different vendors were represented in providing and
processing the TLDs.
During discussions with these vendors, it was determined
that a correction factor of approximately 2.0 should have been applied to the
reported results.
In all cases, this value had not been applied to any of the
actual TLD measurements.
As a result, extremity exposures had been underestimated
by a factor of approximately 2.
Discussion:
At fuel fabrication facilities, as well as at facilities handling natural and
depleted uranium, selected operational processes potentially require extensive
handling of unshielded uranium materials by employees.
Depending on the facility
processes, dose rates to the skin of the extremity from unclad uranium materials
can increase significantly during operations. At fuel fabrication facilities
following introduction of uranium hexafluoride (UF6) into the process, the major
contributor to the skin dose results from ingrowth of the beta-emitting metastable
protactinium-234 (Pa-234m) isotope.
Dose rates through 6-7 mg/cm2 absorbers of
approximately 200 millirem per hour (mrem/hr) for exposure to depleted, natural, or low-enriched unshielded uranium materials in equilibrium with short-lived
daughter isotopes have been reported (References 1-2).
It is the licensee's
responsibility to properly evaluate the potential dose to the skin of the
extremity to determine the need for extremity monitoring, and to verify that no
individual exceeds the exposure limits specified in 10 CFR Part 20.
In using
TLD's for extremity monitoring, licensees should verify that the appropriate
correction factor for the different TLD response between uranium and the
calibration source is used.
No specific action or written response is required by this information notice.
If you have questions about this matter, please contact the technical contacts
listed below or the appropriate regional office.
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety, NMSS
Technical Contacts:
George B. Kuzo, Region II
John Potter, Region II
(404) 331-2560
(404) 331-5571 Attachments:
1. References
2. List of Recently Issued NRC
Information Notices
3. List of Recently Issued NMSS
Information Notices
- See previous concurrence
OFC :IMOB*
- IMOB*
- IMSB*
- IMN
- IMN
NAME :CTrottier/ll:JHickey:CHaughney :G
I$om :R g
g
ham
DATE :2/14/91
/14/91
1 :4 4" /91
IN 91- March , 1991 cesium-based to uranium-based shallow (skin) dose.
Review of the licensee
exposure data indicated that the appropriate correction factor was not applied
to the original results provided by the vendor. For the 1990 data, a beta- correction factor of approximately 1.89 was required and higher exposure
values were subsequently assigned to personnel handling unclad uranium materials.
Further discussion with the TLD vendor laboratory indicated that in addition to
the revisions for the 1990 study, an appropriate correction factor was not
applied to similar measurements conducted by the licensee in 1983 regarding
unshielded uranium material dose rate studies.
Discussion:
At fuel fabrication facilities, as well as at facilities handling natural and
depleted uranium, selected operational processes potentially require extensive
handling of unshielded uranium materials by employees.
Dependent on the
facility processes, dose rates to the skin from unclad uranium materials can
change significantly during operations. At fuel fabrication facilities following
introduction of uranium hexafluoride (UF ) into the process, the major
contributor to the skin dose results frok ingrowth of the beta-emitting
metastable protactinium-234 (Pa-234m) isotope. The ingrowth of the relatively
short-lived Pa-234m radioisotope (1.17 minute physical half-life) follows the
decay of the longer-lived (24.1 day physical half-life) thorium-234 (Th-234)
parent radionuclide. Dose rates through 6-7 mg/cm2 absorbers of approximately
200 millirem per hour (mrem/hr) for exposure to depleted, natural, or
low-enriched unshielded uranium materials in equilibrium with short-lived
daughter isotopes have been reported (References 1-2).
Proper evaluation of the
potential dose to the skin of the extremity is required to determine the
threshold for extremity monitoring, and to verify that no individual exceeds the
exposure limits specified in 10 CFR Part 20.
In selecting TLD's for extremity
monitoring licensees should verify that the appropriate correction factor
for differential TLD response to the uranium and calibration source beta energies
are utilized.
No specific action or written response is required by this information notice.
If you have questions about this matter, please contact the technical contacts
listed below or the appropriate regional office.
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety, NMSS
Technical Contacts: George B. Kuzo, Region II
John Potter, Region II
(404) 331-2560
(404) 331-5571 Attachments:
1. References
2. List of Recently Issued NRC
Information Notices
3. List of Recently Issued NMSS
Information Notices
- See previous concurrence
OFC
- IMOB*
- IMOB*
- IMSB*
- I~X J
IMNS
NAME :CTrottier/ll:JHickey:CHaughney : folom :RECunningham
_____________________________________
DATE :2/14/91
- 2/14/91:2/14/91
- 3/W /91
- 3/ /91
UtCIlAL RLLURU LCUPY
KUZO IN
IN 91- February , 1991 provided by the vendor. For the 1990 data, a beta-correction factor of
approximately 1.89 was required. Applying the correction factor resulted in
dose rates of 72 and 76 mrem/hr for the monitored unshielded results.
Further
discussion with the TLD vendor laboratory indicated that in addition to the
revisions for the 1990 study, an appropriate correction factor was not applied
to similar measurements conducted by the licensee in 1983 regarding unshielded
uranium material dose rate studies.
Discussion:
Selected processes at fuel fabrication facilities as well as natural and depleted
uranium facilities potentially require extensive handling of unshielded uranium
materials by employees.
Following introduction of uranium hexafluoride (UF 6 )
into the fabrication process, the major contributor to the skin dose results from
ingrowth of the beta-emitting metastable protactinium-234 (Pa-234m) isotope. The
ingrowth of the relatively short-lived Pa-234m radioisotope (1.17 minute physical
half-life) follows the decay of the longer-lived (24.1 day physical half-life)
thorium-234 (Th-234) parent radionuclide. Dose rates through 6-7 milligrams per
square centimeter (mg/cm2) absorbers ranging from approximately 100 to 200
millirem per hour (mrem/hr) for exposure to depleted, natural, or low-enriched
unshielded uranium materials in equilibrium with short-lived daughter isotopes
have been reported (References 1-3).
Proper evaluation of the potential dose to
the skin of the extremity is required to determine the threshold for extremity
monitoring, and to verify that no individual exceeds the exposure limits specified
in 10 CFR Part 20.
In selecting TLD's for extremity monitoring licensees should
verify that the appropriate correction factors are utilized.
No specific action or written response is required by this information notice.
If you have questions about this matter, please contact the technical contacts
listed below or the appropriate regional office.
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety, NMSS
Technical Contacts: George B. Kuzo, Region II
(404) 331-2560
John Potter, Region II
(404) 331-5571 Attachments:
1. References
2. List of Recently Issued NRC
Information Notices
3. List of Recently Issued NMSS
Information Notices
-
X
.
- F
IMOB
0d
A
2 IN
IP
)ATE
_
2/_-/91
______
1
---
/_91------___------------------------_--_____
_____
-___ _ --
4AME :CTrottier/ll:JHickey:C aughney :GSjoblom :RECunningham
Z---------------------T --------------------------- _--------------------------------------------
)ATE :2/ty/91
- 24 h91 :212
91
- 21 /91
- 2/ /91
OFFICIAL RECORD COPY
IN/DOSIMETERS