United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-81: Problems Resulting in Erroneously High Reading with Panasonic 800 Series Thermoluminescent Dosimeters

                                               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.  


.

                                                 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


Page Last Reviewed/Updated Tuesday, November 12, 2013