ML20137C254
| ML20137C254 | |
| Person / Time | |
|---|---|
| Issue date: | 03/21/1997 |
| From: | Steven Baggett NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Camper L, Combs F, Piccone J NRC |
| References | |
| SSD, NUDOCS 9703240194 | |
| Download: ML20137C254 (1) | |
Text
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l March 21, 1997 NOTE TO:
Generic Assessment Panel Fred C. Combs Larry W. Camper Josephine M. Piccone Kevin M. Ramsey l
FROM:
Steven L. Baggett, Section Leader Sealed Source Safety Section l
Medical, Academic, and l
Commercial Use Safety Branch l
Division of Industrial and Medical Nuclear Safety, NMSS
SUBJECT:
REQUEST TO EVALUATE GENERIC IMPLICATIONS OF l
MODEL M43A1 FAILURES The following information is provided to the Generic Assessment Panel in response to your request for analysis of the letter dated January 23,1997, from the U.S. Army to the NRC, regarding generic implica+ ions of the failures of model M43A1 detectors. Based on review of the information in the an alysis, it does not appear that there is a current need for action.
Corrosion between the Au and Allayers and the removal of this corrosion and radioactive material is a materials issue and occurs to some degree at all times, even on new sources.
This is due to moisture penetrating the gold and gold / americium layers through the pores that are naturally in the materials. The moisture can eventually penetrate all the way to the aluminum layer, causing galvanic corrosion between the dissimilar metal layers. This corrosion product which can contain americium, along with americium in the gold / americium layer, can j
migrate with the moisture to the foil surface. Over time, this process is accelerated by radiation-induced damage, which ir; creases the areas for the moisture to penetrate the layers.
The failures identified by the Army used a threshold of 20 dpm, which is significantly below the 1
NRC reporting level of 0.005 microcurie (equivalent to 11,100 dpm). The Army lowered its threshold to 20 dpm and changed the leak test frequency for the device from three years to one yearin January 1995. The sudden increase in the number of failures appears to be more a i
function of the lowered threshold and more frequent testing than a function of a sudden deteriorating of the souices. The Army reports that there are over 30,000 M43A1 units in use by the Army. In 1995 and 1996, after the lowering of the threshold, the Army reports that a total of 59 failures were identified, which is less than 0.2% of the units in use. Most of these failures have been in the range of 20-100 dpm, with occasional ones over 100 dpm. The Army reports that there have been none reaching 200 dpm. By NRC definition, none of these reported sources would be considered leaking sources. Based on the information in the analysis, leak testing appears to be an adequate means for identifying potentially significant deteriorating sources in these types of devices. The Army is continuing to monitor the situation, and plans to take any further action as warranted if the failure rate or the average contamination per unit increases.
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/ e t-Distribution:
Ticket # IMNS 5688 NR-0155-D-118-SSSS r/f IMAB r/f NE02-SSD-7 DOCUMENT NAME: C:\\SSSS\\ TICKETS \\lMNS5688. GAP Te rec **ve a copy of this document, Indicate in the box: "C" = Copy without at*.schment/ enclosure
'E" = Copy with attachment / enclosure "N" = No copy i
OFFICE IMAB
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l NAME MBurgess/mb MLA -
SBaggett DATE 03/ 2l /97 03/ % /97 OFFICIAL RECORD COPY 9703240194 970321