Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
IN 85-81
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
October 17, 1985
Information Notice No. 85-81: PROBLEMS RESULTING IN ERRONEOUSLY HIGH
READING WITH PANASONIC 800 SERIES
THERMOLUMINESCENT DOSIMETERS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or
a construction permit (CP) and certain materials and fuel cycle licensees
who may use the subject thermo-luminescent dosimeters (TLDs).
Purpose:
Information Notices IN 82-42 "Defects Observed in Panasonic Model 801 and
802 TLD's" and IN 85-42 "Loose Phosphor in Panasonic 800 Series Badge TLD
Elements" discussed two separate problems with Panasonic TLD's that
resulted in erroneous exposure measurements with the badges.
This information notice is provided to inform the licensees of two
additional problems that have resulted in erroneously high readings with
Panasonic 800 series TLD's. It is expected that licensees, will review
this information for applicability to their facilities and consider
actions, if appropriate, to preclude a similar problem occurring at their
facilities. However, suggestions contained in this information notice do
not constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances:
1. Self-Irradiation From Contaminated Lead Filters:
Several Panasonic TLD users have recently experienced anomalously high
readings. On investigation, it was determined that the lead filters in the
badges were contaminated with trace amounts of naturally occurring
radioisotopes. The lead filters (on both sides of the TLD elements) are
used to compensate for the energy dependence of calcium sulfate phosphor.
The lead used for these filters appears to be contaminated with
radium-226 daughters. Bismuth-210 is a major dose contributor. Low level
radiation from these contaminants contributed up to 15 mrem in 30 days to
the TLD elements. During the initial investigation of the anomalous
readings, several TLD badges were counted using a gamma spectroscopy
system. This technique was unable to identify contaminated lead filters
because of the low activity of gamma emitting contaminants. However, when
lead filters were recounted using a thin window Geiger-Muller (GM)
detector, they were found to be contaminated with beta emitting
radioisotopes.
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IN 85-81
October 17, 1985
Page 2 of 3
Panasonic TLD'S can be screened for contaminated filters by placing
several in a low background thin-window GM counter Licensees wishing to
use this screening technique should select a counting time sufficient to
provide an acceptable lower limit of detection (5 pCi beta per gram of
lead) for their system. Panasonic is currently negotiating the
replacement of badges on a case-by-case basis.
Abnormal TLD Readings Caused by Hydrogen Sulfide (H2S) Gas
On May 6, 1985, an unexpectedly high reading was indicated during a
routine TLD processing of a terminating contract worker leaving the
Brunswick Steam Electric Plant. The worker had been employed to clean
marine life out of the plants intake structure, an area where no
radiation is expected. He was issued a TLD because access to the job site
was through the plant's protected area. The worker's TLD (Panasonic Model
UD-802) indicated 13,500 and 457 millirem on elements 1 and 2,
respectively (both lithium borate TLD material), with 1.2 and 1.4
millirem indicated on elements 3 and 4, respectively (calcium sulfate TLD
material). On investigation, the licensee has concluded that the abnormal
TLD response was caused by exposure to H2S gas given off by the decaying
marine life in the intake structure. Extensive testing by the licensee
indicates that exposure to H2S causes gross over response from lithium
borate TLD material. Multiple exposures to concentrations as low as 10
parts per million (ppm) over a 12-hour period caused responses that
correspond to 250 millirem of radiation exposure. Indication as high as
4870 millirem were obtained from a 4-hour exposure to 114 ppm H2S.
Several agents (such as chemical contaminants, ultraviolet light or
extreme humidity) are known to cause abnormal TLD responses. Licensees
may wish to provide appropriate means of protecting the TLD when exposure
to these agents is likely. However, licensees should ensure that
protective coverings or containers do not inhibit the TLD's ability to
properly respond to actual radiation exposure.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: Roger Pedersen, IE
(301)492-9425
Jim Wigginton, IE
(301)492-4967
Attachments: List of Recently Issued IE Information Notices
