ML20211G192
| ML20211G192 | |
| Person / Time | |
|---|---|
| Issue date: | 12/01/1983 |
| From: | Pettijohn S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20211G133 | List: |
| References | |
| TASK-AE, TASK-N306 AEOD-N306, NUDOCS 8611030236 | |
| Download: ML20211G192 (3) | |
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AEOD ENGINEERING EVALUATION
- UNIT: N/A EE REPORT No.: AEOD/N306 LICENSE No. 15-13812-01 DATE: December 1, 1983 Licensee: AIR FORCE, DEPARTMENT OF EVALUATOR / CONTACT: SPettijohn (ScCONNELL AIR FORCE BASE)
SUBJECT:
POTENTIALLY LEAKING AMERICIUM-241 SOURCES MANUFACTURED BY AMERSHAM CORPORATION
SUMMARY
The Department of the Air Force McConnell Air Force Base, reported to NRC by letter dated December 27, 1982, that three americium-241 foil sources, Model AMM,
- manufactured by Amersham Corporation were found to be leaking during the routine 1eak testing of sealed sources. The sources are contained in ion chambers which are used in gas analysers for detecting explosive gases.
AEOD/Nonreactor Assessment Staff (NAS) undertook a review to determine if there was a general problem of source leakage with this particular type of source (Model AMM - max activity 600 microcuries americium) and to assess any associated health and safety problems.
The.use of these sources is scheduled by the Air Force to be phased out by 1987.
No additional. sources; are curre,ntly scheduled to be procured by the Air Force.
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From our evaluation,~we concluded that there is not a leakage problem with the foil source itself. However, the process (brazing) used by Amersham to attach the foil sources to the ion chambers in which they are contained and the corrosive atmosphere to which the sources are exposed at McConnell and other installations may affect the life of the sources.
It is our understanding that McConnell's license is in the renewal process.
We suggest that NMSS specifically review McConnell's leak detection program during the license renewal process because the sources have higher than normal leakage probability (as a result of the brazing operation and exposure to a corrosive atmosphere).
DISCUSSION The U.S. Air Force McConnell Air Force Base, Kancas, has an NRC license (No.
15-13812-01) to possess and use americium-241 sources (manufactured by Amersham Corporation) in explosive gas analysers (as part of a missile safety system).
In a report dated December 27, 1982, McConnell reported that three leaking americium-241 sources had been discovered during routine leak testing of sources.
One source was found during leak testing of sources in May, August, and October of 1982. Two of the sources found to be leaking (May and August) had not been put in service prior to the leak test; all sources were returned to Amersham.
AEOD/NAS undertook an engineering evaluation to determine the extent of the source leakage problems. Americium-24) is an alpha emitter and in some forms easily dispersible. Therefore, leaking americium-241 sources could cause significant health and safety problems as well as have significant economic consequences (decontamination cost).
8611030236 831201 PDR ORG NEXD PDR
- This report supports ongoing AEOD and NRC activities and does not represent the m position or requirements of the responsible NRC program office.
The caericium sourcss in qu2stien cra foil sources utde from a gold-americium oxide mixture contained between a silver backing, approximately 6 mils in thickness, and a front covering of gold or gold and palladium approximately 0.002 mm thick.
The active area does not extend to the end of the foil. The foil source is installed in an ion chamber by soldering the ends of the foil to the inside wall of a cylinderical ion chamber.
NAS discussed the report from McConnell Air Force Base with Captain Reginald K. Y. Ching and Captain DeLucca of the Bioenvironmental Engineering Group at McConnell (Captain Ching signed the report submitted to the NRC). They provided the following information. ,
The Bioenvironmental Engineering Group'at McConnell has the responsibility for Am-241 sources.at McConnell and at other installations that use the devices.
All new or replacement sources installed in ion chambers are sent by the supplier to the Bioenvironmental Engineering Group at McConnell for transfer to the end user.
If a source is received from the supplier without a leak test certificate, then the ion chamber is wiped for contamination by personnel at McConnell. Other ion chamber sou'rces in use in the field are wiped at six-month intervals.
The gas analysers* using the ion chambers are used for detecting explosive gases.
The ion chamber and Am-241 foil source are exposed to atmospheres containing both violent reducing agents and violent oxidizing agents. The ion chamber (which contains the Am-241 source) remains installed in the gas analyzer unless the chamber fails (this occurs on occasion and is related to the corrosive atmosphere) or unless the Am-241 source is found to be leaking (the sources are leak test every six months). Ion chambers that are found to contain leaking sources are returned to the supplier for repair or disposal. A new or repaired ion chamber containing an Am-241 source is installed in the gas analyser.
- Captain Ching stated that the two new ion chambers (chambers that had not been put in service) referenced in the December 27, 1982, letter to NRC were the only new chambers found to be leaking. He said that several chambers in normal use were found to contain leaking sources during the six-month leak test periods in 1982.
The leakage is believed to have been caused by the corrosive atmosphere.
The increase in the number of reported leaking sources in 1982 is probably due to improvements in the licensee's radiation safety program that began in 1982 according to Captain Ching. (AEOD does not have any reports other than the ones referenced.) Leaking sources are returned to Amersham for disposal or repair.
The use of the Billion-Aire gas analysers is s'cheduled to be phased out by 1987.
The Air Force is planning to discontinue use of the gas analysers af ter this period and return all material to Amersham. No additional ion chambers are scheduled to be procured by the Air Force.
NAS Dr. D.also discu'ssed Coppell the leaking sources with Mr. J. Buchenberaer and of Amersham.
They indicated that Amersham's procedures require that all source / ion chamber units be leak tested before being shipped to customers and that Amersham has not found a generic leakage problem with the i Model AMM Am-241 source / ion chamber used in the Billion-Aire gas analyser.
Amersham indicated that the likely cause of the leaking sources reported by McConnell was the technique used to secure the foil source to the inside wall of the ion chamber.
Billion-Aire Model 706CA manufactured by Mine Safety Appliance Company.
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Dr. Coppell indicated that on some occasions this technique of installing the foil in the ion chamber has resulted in leaking sources. Dr. Coppell also stated that as an economy measure the Air Force had begun requiring that defective ion chambers be reworked with new foil sources being installed. This made the brazing process more difficult and increased the probability of a source being a leaker.* Amersham has discontinued supplying this source installed in an ion chamber and Dr. Coppell indicated that if Amersham should resume supplying this type of service a new method would be used to install the foil source.
_ FINDINGS The cause of the source leakage appears to be the brazing technique used to attach the foil sources to the inside walls of the ion chambers and the corrosive atmosphere in which the sources are used. Only two sources were reported leaking before being put into use (this leakage was likely due to the brazing technique). Although McConnell stated that several sources have been found leaking af ter being in use for at least six months, this leakage appears to be due to the corrosive atmosphere in which the sources are used. All sources are required to be leak tested at six-month intervals and any sources found to be leaking are replaced.
CONCLUSIONS Although the sources reported as Ic hing were actual leakers, there is no evidence based on our discussion with the licensee, the source manufacturer, and a review of reports of leaking sources, that there is any general leakage problem with this particular source before it is put in service.
It is our understanding that McConnell's license is in the renewal process. '
We suggest that NMSS specifically review McConnell's leak detection program during the license renewal process because the sources have higher than normal leakage probability (as a result of the brazing operation and exposure to a corrosive atmosphere).
- A 1974 AEC memorandum that referenced Mine Safety Appliance Company (MCA),
the manufacturer of the Billion-Aire trace gas analyser in which the ion chamber /Am-241 source is used, stated that Nuclear Radiation Development Corporation (NRD), another supplier of this ion chamber /Am-241 device found that brazing of Am-241 foils to the detector housing caused leakage and contamination.
NRD stopped brazing and used a spring or svage fit to install the foils inside the detector housing.