Stainless Steel Contamination
Stainless Steel Contamination
(OP)
I am new here
, and i'm an engineering intern, not a real engineer...but i'm trying to find out if there is any way that an oil-filled capacitor with a stainless steel case can become contaminated with cobalt-58 or 60. I was told that when heated the metal becomes pourous and absorbs small particles of cobalt-60, which then becomes trapped in the metal upon cooling. The capacitor has been thoroughly cleaned on the outside and is still contaminated. I beleive the dose-rate on the capacitor was approx. 50 rad/hour, and the capacitor has been in service for 3 years. Any help would be awesome.
, and i'm an engineering intern, not a real engineer...but i'm trying to find out if there is any way that an oil-filled capacitor with a stainless steel case can become contaminated with cobalt-58 or 60. I was told that when heated the metal becomes pourous and absorbs small particles of cobalt-60, which then becomes trapped in the metal upon cooling. The capacitor has been thoroughly cleaned on the outside and is still contaminated. I beleive the dose-rate on the capacitor was approx. 50 rad/hour, and the capacitor has been in service for 3 years. Any help would be awesome.





RE: Stainless Steel Contamination
RE: Stainless Steel Contamination
If the alloy is an austenitic stainless steel (304, 316 are examples), then the composition sometimes lists the Nickel content as "nickel + cobalt" and has a small amount of cobalt present as a tramp element. If this capacitor is in a high rad area, then I would expect neutron bombardment to affect the cobalt directly.
RE: Stainless Steel Contamination
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Plymouth Tube
RE: Stainless Steel Contamination
How are you characterizing the contamination? Are you doing a AES (Auger Electron Spectroscopy) Analysis, EDS (Energy Dispersive Spectroscopy), or SIMS (Secondary Ion Mass Spectrometry)? Low abundance isotopes such as cobalt 58 can only be detected using SIMS. Cobalt-59 is the only stable and therefore the highest abundant cobalt isotope. In fact, naturally occurring cobalt is made up of 99 At% Cobalt-59. What is the source of radiation? The reason being that knock-on damage of a atoms core can occur as a result of high energy bombardment.
RE: Stainless Steel Contamination
agmotes
RE: Stainless Steel Contamination
RE: Stainless Steel Contamination
agmotes
RE: Stainless Steel Contamination
The use of SS scrap is common, but I don't think radiologically contaminated scrap used in new stainless steel is the source of your contamination issue.
RE: Stainless Steel Contamination
I'm still wondering why you believe you are detecting Cobalt-58 or Cobalt-60 in your oil capacitor instead of the stable cobalt-59 isotope. If in fact you are detecting Co-58 or Co-60 you will have to change the ways you are disposing of the cooling oil.
RE: Stainless Steel Contamination
UconnMaterials: I'm not sure as to the survey instrumentation Agmotes is using, but I do know our nuclear plant's HP department claims they can identify the actual isotope that is decaying based upon what comes off the isotope.
RE: Stainless Steel Contamination
I had been told before (obviously this was wrong) that cobalt-60 was mainly formed from cobalt-58, upon further research and your guidance I realize that the majority of the contamination must have come from either contaminated scrap SS, or tramp cobalt-59 to cobalt-60 from the neutron source. Sorry for the confusion, and SMF1964 is right about RP telling us that it was cobalt-60 on or in the capacitor. Again, we do a test to check for contams before installing components, are you suggesting that there may be nonradioactive materials in the scrap that are becoming radioactive over time?
agmotes
RE: Stainless Steel Contamination
But stranger things have happened.
RE: Stainless Steel Contamination
Examining the decay mode certainly would be a way to narrow down the isotope. The Wikopedia lists Co-59 as decaying by electron capture and in this case a neutrino gets emitted. I'm not a nuclear physicist (but rather a materials scientist) and therefore cannot comment on how to detect a neutrino. The best way to detect an isotope is to use SIMS analysis. I've ion implanted Cr-52 into high speed steel and been able to do depth profiling chemical analysis with a SIMS unit that detected just the Cr-52 isotope alone. SIMS allows one to sort atoms based on atomic mass.
agmotes,
Certainly, if one bombards an atomic core with high energy neutrons the atomic core will become damaged and/or the neutron will become implanted into the core. Besides nickel, tramp cobalt is probably the heaviest element in stainless steel and therefore is more likely to be effected by neutron bombardment than say iron or chromium. This begs the question of why just radioactive Co-60 was found and not any nickel isotopes.
RE: Stainless Steel Contamination
agmotes
RE: Stainless Steel Contamination
With regard to contamination of 'new' steel from scrap - I just wiki'd Cobalt-60 and found reference to a March 1 2008 incident. Wow.