Information Notice 1991-30, Inadequate Calibration of Thermoluminescent Dosimeters Utilized to Monitor Extremity Dose at Uranium Processing and Fabrication Facilities

Inadequate Calibration of Thermoluminescent Dosimeters Utilized to Monitor Extremity Dose at Uranium Processing and Fabrication Facilities

ML031210652
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	04/23/1991
From:	Cunningham R NRC/NMSS/IMNS
To:
References
IN-91-030, NUDOCS 9104170066
Download: ML031210652 (10)

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 -/

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IN 91-30

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

uranium. 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. Doserates 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.

IN 91-30

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 IN 91-30

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 IN 91-30

April 23, 1991 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

86-21, Recognition of American 04/12/91 All holders of OLs or CPs

Supp. 2 Society of Mechanical Engi- for nuclear power reactors

neers Accreditation Pro- and all recipients of

gram for N Stamp Holders NUREG-0040, "Licensee Con- tractor and Vendor Inspection

Status Report" (White Book).

91-29 Deficiencies Identified 04/15/91 All holders of OLs or

During Electrical Distri- CPs for nuclear power

bution System Functional reactors.

Inspections

91-28 Cracking in Feedwater 04/15/91 All holders of OLs or

System Piping CPs for pressurized water

reactors (PWRs).

91-27 Incorrect Rotation of 04/10/91 All holders of OLs or

Positive Displacement Pump CPs for nuclear power

reactors.

89-90, Pressurizer Safety Valve 04/10/91 All holders of OLs or

Supp. 1 Lift Setpoint Shift CPs for nuclear power

reactors.

91-26 Potential Nonconservative 04/02/91 All fuel cycle licensees

Errors in the Working Format and other licensees, in- Hansen-Roach Cross-Section cluding all holders of

Set Provided with The Keno operating licenses for

and Scale Codes nuclear power reactors, who use physics codes to

support criticality

safety in the use of

fissile material.

91-25 Commercial-Grade Structural 04/01/91 All holders of OLs or

Framing Components Supplied CPs for nuclear power

As Nuclear Safety-Related reactors.

Equipment

OL = Operating License

CP = Construction Permit

• Attachment 3

, IN 91-30

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 Potential Nonconservative 04/02/91 All fuel cycle licensees

Errors in the Working Format and other licensees, in- Hansen-Roach Cross-Section cluding all holders of

Set Provided with The Keno operating licenses for

and Scale Codes nuclear power reactors, who use physics codes to

support criticality

safety in the use of

fissile material.

91-23 Accidental Radiation Over- 03/26/91 All Nuclear Regulatory Cc

exposures to Personnel due mission (NRC) licensees

to Industrial Radiography authorized to use sealed

Accessory Equipment Malfunc- sources for industrial

tions radiography.

91-16 Unmonitored Release Pathways 03/06/91 All fuel cycle facilities

from Slightly Contaminated Re- cycle and Recirculation Water

Systems At A Fuel Facility

91-14 Recent Safety-Related Inci- 03/05/91 All Nuclear Regulatory

dents at Large Irradiators Commission (NRC) licensee

authorized to possess anc

use sealed sources at

large irradiators.

91-03 Management of Wastes Contam- 01/07/91 All medical licensees.

inated with Radioactive

Materials ("Red Bag" Waste

and Ordinary Trash)

91-02 Brachytherapy Source Management 01/07/91 All Nuclear Regulatory

Commission (NRC) medi- cal licensees author- ized to use byproduct

material for medical

purposes.

IN 91-30

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 91-30

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

uranium. 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

6-7 mg/cm 2 absorbers of

protactinium-234 (Pa-234m) isotope. Dose rates through

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 ham

g

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)

mg/cm 2 absorbers of approximately

parent radionuclide. Dose rates through 6-7

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 (UF6 )

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 A 2 IN 0d

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IN/DOSIMETERS