ML20058F356
| ML20058F356 | |
| Person / Time | |
|---|---|
| Issue date: | 10/26/1990 |
| From: | Dan Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Haughney C NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| NUDOCS 9011080236 | |
| Download: ML20058F356 (4) | |
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F 007.2 6 1990 l
n MEMORANDUM FOR: Charles J. Haughney, Chief Fuel Cycle Safety Branch Division of Industrial and Medical l
Nuclear Safety
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FROM:
Douglas M. Collins, Chief Emergency Preparedness and Radiological Protection Branch
'j Division of Radiction Safety and Safeguards 1
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SUBJECT:
TRANSMITTAL OF DRAFT INFORMATION NOTICE ON BETA DOSE 4
EX1REMITY MONITORING AT FUEL FABRICATION FACILITIES i
4 This memorandum. transmits for your information and possible use the subject draft -Information Notice.
As a result of potential skin dose assessment
. inadequacies identified at several Region 11 fuel fabrication facilities, we j
fee' this Notice may help negate possible existing dose evaluation concerns-at l
other facilities.
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. If you have any questions, please call me at FTS 841-5586.
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OttGNAs." SIGNED W DOUCI AS A m.1NS Douglas M. Collins l
Enclosure:
. Draft Information Notice-J cc w/ enc 1:
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r UNITED STATES NUCLEAR REGULATORY COMMISSION 0FFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS WASHINGTON, D.C. 20555 October,,, 1990 NRC INFORMATION NOTICE NO. 90 _: BETA DOSE EXTREMITY MONITORING AT FUEL FABRICATION F ACILITIES
, Addressees:
All fuel cycle licensees and other licensees routinely handling unciad uranium materials.
Purpose:
This information notice is being provided to alert addressees to potential problems resulting from inadequate vendor processing 'of thermoluminescent dosimetry utilized to'. monitor extremity skin dose at fuel fabrication facilities.
It' is expected that licensees will review the information for applicability to their facilities and ' consider actions, as appropriate, to avoid similar problems.
However, suggestions contained in this Information Notice do not constitute U.S.
Nuclear Regulatory Commission (NRC) requirements; therefore, no specific action or written response'is required.
De s c r i p t_i_on_,o,f C i rc ums t a nc e s :
. Selected-processes such-as grinding, press and inspection operations at-fuel-fabrication facilities potentially require extensive contact (handling) of unciad uranium materials.by' employees.
Following introduction of uranium hexafluoride (UF6)! intothe fabrication process, the major contributor to the skin dose -
results from ingrowth of the beta-emitting nietastable 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.
For unshielded uranium' materials ~in equilibrium with short-lived daughter isotopes, dose rates through a 7 milligrams per square centimeter.(mg/cm ) absorber ranging from 100 e
to 200 millirem per hour (mrem /hr) have been reported.
Proper evaluation of the dose to the skin of the extremity is required to determine the threshold for extren:ity monitoring requirements and to verify that no individual exceeds the exposure limits specified in 10 CFR Part 20.
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- During August - September 1990, an NRC licensee conducted evaluations of i
extremity skin exposures for selected personnel handling unclad uranium l
materials.
The evaluation included both extremity monitoring for workers L
handling the unciad materials and, in addition, a determination of the dose rate
.from unshieldec uranium material.
Monitoring was conducted using single chip TLDs mounted )v plastic finger rings which were supplied and subsequently
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- processed by a vendor laboratory.
The licensee had verbally discussed with the vendor that the monitoring with the finger ring TLDs was conducted to determine employee skin dose from exposure to the Pa-234m beta particle, 2.29 MeV maximum energy, in the unclad uranium materials.
In addition, the licensee included instructions indicating the type of radioactive materials to be monitored with their purchase agreement accompanying the TLDs to the processing vendor l
laboratory.
For the TLDs utilized to monitor pellet dose rates, the. vendor reported pellet exposure rates of 28 and 40 mrem /hr as determined through a density absorber thickness of 7 mg/cm.
Initially, the licensee assumed the measurements to be r
accurate and no additional calculations were made to support the vendor measurements. However, in response to NRC inquiries, calculations indicated dose rates were expected to be approximately 65 percent of equilibrium values based on the 35 -to 40 day interval between the introduction of UF6 into the fabrication process and_ when the actual measurements of the unclad materials were conducted.
Assuming the range of dose rates for uranium materials reported in the i
literature, the calculated minimum dose rate for the pellet material was expected i
to exceed 65 mrem /hr.
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'During discussion of the dose measurements with the TLD vendor, the licensee was' informed that the TLDs were calibrated with a cesium-137 (Cs-137) source which t
results in a uniform energy deposition within-the TLD.
Errors result when the energy deposited is nonuniform as a result of attenuation, such as for beta particle irradiation from uranium.
The vendor had a calibration factor for TLDs exposed to a uranium slab and-noted that a correction factor was required te convert.from a cesium-based to uranium-based shallow (skin) dose.
Review of the licensee _ exposure data indicated that the appropriate correction factor was not i
applied toithe original _ results 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 andl6 mrem /hr for the monitored unciad. uranium materials.
These values were consistent _with the calculated resul ts.-
Furt'er discussion with the TLD vendor laboratory indicated that in addition to tte revisions for the 1990 study, a required correction factor was not applied to similar measurements conducted by the licensee in'1983 regarding unciad uranium material dose rate studies.
For those data, a separate correction factor. of approximately 2.21 resulted.from differences in the finger ring
'i absorber materials used for the 1983 and 1990 measurements.
The licensee upgraded their procedures to verify that the appropriate beta-correction factors were included with processing of TLDs utilized to measure skin.
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In addition, the. licensee proposed to conduct systematic TLD dose
- 'surements of 'unciad. uranium material through time to determine the expected e rates during ingrowth and at equilibrium for the beta-emitting Pa-234m. The
,uilibrium values could be used to evaluate potential exposure and corroborate
.ctual measurements.
.,ubsequently, a NRC Region 11 representative discussed with representatives from four_ additional fuel fabrication facilities, TLD evaluations of skin exposure from depleted or low enriched unciad uranium material.
The facilities utilized single chip TLD devices processed by vendor laboratories. Among the facilities, f
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three different vendors were represented in providing the TLDs and their subsequent processing.
Licensee representatives were informed that correction factors, approximately two times the reported values, were required to calculate the accurate skin dose from the uranium material.
However, correction factors were not -applied to any of the actual TLD measurements conducted.
Licensee representatives took apprapriate inmediate action to verify ~that all exposures s
were below 10 CFR Part 20 limits.
Selected licensees were conducting and documenting detailed studies to determine accurate unclad uranium dose rates for future evaluations.
'No specific. action or written response is required by this inforn.ation notice.
-If you have questions about this matter, please contact the technical contacts
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t listed below or. the Regional Administrator of the appropriate regional office.
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Richard E. Cunningham, Director Division of Industrial and Medical Nuclear Safety 1
Office of Nuclear Material Safety I
and Safeguards I
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' Technical Contacts: George B. Kuzo, Region II (404) 331-2560 George H. Bidinger, NNSS
Attachment:
List of Recently Issued NRC Information Notices i
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