Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 85-42
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
May 29, 1985
Information Notice No. 85-42: LOOSE PHOSPHOR IN PANASONIC 800 SERIES
BADGE THERMOLUMINESCENT DOSIMETER (TLD)
ELEMENTS
Addressees:
All holders of a nuclear power plant operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is provided to alert NRC licensees to a problem
noted in some Panasonic 800 series TLD badges that has caused spurious high
readings in one of the badges' TLD elements. This information is intended to
assist licensees in diagnosing any spurious readings with the Panasonic TLD
system.
It is expected that recipients will review the information provided for
applicability, if appropriate, to their dosimetry programs. However,
suggestions contained in this information notice do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances:
The Panasonic 800 series TLD badge contains a card that holds four TLD
elements. Each TLD element consists of a thin film of TL phosphor attached
to a disk backing with a clear teflon bubble cover. During reading, the
phosphor is heated by converging infrared light on the backing. The
luminescence from the phosphor (which is proportional to the dose received)
radiates through the teflon cover and is read with a photomultiplier tube.
Several Panasonic TLD users (including NRC's Region I) have identified
badges where crystals of the phosphor have detached themselves from the
backing of the element, resulting in high erratic readings in that element.
When viewed through a stereoscopic microscope, phosphor crystals can be
observed sticking to the teflon cover (presumably by electrostatic charge).
In this position, the loose TL material is not in contact with the backing
and does not get heated when the badge is read. These TL crystals remain at
an elevated energy state and continue to accumulate dose. Apparently
erratically high readings result when the loose crystals are shaken back
onto the backing surface during a subsequent reading. They are then heated
and luminescence proportional to the total doses received during several
read cycles is produced. This process can cause the affected element to
erroneously read as much as an order of magnitude higher than the other
elements in the same card. Although the
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IN 85-42
May 29, 1985
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frequency of occurrence is small (one licensee found only one problem badge
in 30,000), there is evidence that the frequency increases substantially
once the badges have been through 100-200- read cycles.
Panasonic has a manufacturing quality control (QC) specification on the
amount of loose phosphor in an element. However, physical shock and thermal
cycles, experienced during badge use, appear to loosen additional material.
Panasonic has stated that they have modified their QC program to provide a
greater physical challenge to the badge before they are screened. For those
badges already in use, licensees can visually inspect any TLD elements
suspected of having loose TL crystals. Panasonic has been exchanging badges
identified as having excessive loose TL material.
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 of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: R. L. Pedersen, IE
(301) 492-2967
J. E. Wigginton, IE
(301) 492-9425
Attachment: List of Recently Issued IE Information Notices
