intake

[wlrun3@aol.com]

 
   ...during recent cavity decon at lasalle worker was told 120 nCi intake Co60 only, 10 mR, week to clear...

   ...my personal experience, 80 nCi intake Co60 only, took a year to go non-detectable (10 nCi) by fastscan...

   ...Co60 bio T1/2 is 9.5 d so effective T1/2 has to be less...

   ...from 120 nCi to 7.5 nCi, 4 bio T1/2's is roughly 40 days...

   ...why was the worker told a week when it looks like it should have been more than a month...

   ...why was i detectable (>10 nCi) by fastscan for a year when it looks like it should have been less than a month...

[UncaBuffalo]

 
   ...during recent cavity decon at lasalle worker was told 120 nCi intake Co60 only, 10 mR, week to clear...

   ...my personal experience, 80 nCi intake Co60 only, took a year to go non-detectable (10 nCi) by fastscan...

   ...Co60 bio T1/2 is 9.5 d so effective T1/2 has to be less...

   ...from 120 nCi to 7.5 nCi, 4 bio T1/2's is roughly 40 days...

   ...why was the worker told a week when it looks like it should have been more than a month...

   ...why was i detectable (>10 nCi) by fastscan for a year when it looks like it should have been less than a month...

My guess would be the location & chemical form of the Co-60. 

Soluble would have the 9.5 day biological halflife you are quoting.

If it was insoluble & got into the GI tract, it would easily pass in less than a week.  This has been my experience with the internal exposures I have received.   A couple of days of not being able to clear the portals...then home free.  (My highest was 271 nCi mixed activation isotopes at WNP-2.  They gave the whole cavity decon crew 'Get-Out-of-Jail-Free' cards for the PCMs so we could still work in the RCA.)

If the isotope was an insoluble form that got lodged in the lungs, then a longer retention time (as in your case, Bill) makes sense.

So, for the La Salle worker, I have 2 thoughts.  Either:
1.  The person saying a week didn't understand halflife...and just quoted 9.5 days as the total time...
or
2.  The person saying a week had good historical perspective on how La Salle uptakes intakes clear themselves and knew that most of the Co-60 would just pass through, so was confident saying it'd all be over in less than 7 days.

Does that match your thoughts?

[wlrun3@aol.com]

   ...i think you're right about the body count operator knowing from plant experience...

   ...from 10cfr20...

   ..."the ali's and dac's for inhalation are given for three classes (D,W,Y) of radioactive material, which refer to their retention (approximately days, weeks and years) in the pulmonary region of the lung. This classification applies to a range of clearance half times of less than 10 days for D, for W from 10 to 100 days, and for Y greater than 100 days."

   ..."W class...all compounds except those given for Y"
   ..."Y class...oxides, hydroxides, halides, and nitrates"

   ...my intake was from bead blasting turbine diaphragms on the turbine deck...

   ...the workers' intake was from the reactor cavity...

   ...does this mean that the Co60 in the turbine is Y class and the Co60 in the cavity is W class...

   ...if so does that mean that the Y class is insoluble and impinges on the turbine diaphragms (and my lungs) while the W class is soluble and passes through the reactor cavity worker rapidly...

   ...how does solubility affect uptake into the blood, as opposed to intake, and how does that affect cede from the intake...

   cede = (intake/sALI)5rem
          = (.120 uCi/3E+1)5rem
          = .02 rem
          = 20 mrem

   

[retired nuke]

 
   ...during recent cavity decon at lasalle worker was told 120 nCi intake Co60 only, 10 mR, week to clear...

   ...my personal experience, 80 nCi intake Co60 only, took a year to go non-detectable (10 nCi) by fastscan...

   ...Co60 bio T1/2 is 9.5 d so effective T1/2 has to be less...

   ...from 120 nCi to 7.5 nCi, 4 bio T1/2's is roughly 40 days...

   ...why was the worker told a week when it looks like it should have been more than a month...

   ...why was i detectable (>10 nCi) by fastscan for a year when it looks like it should have been less than a month...

IMHO;
If that was the original "post shower" fastscan - then the majority of what was detected was probably GI tract / upper respiratory - this is "intake"- and will mostly be gone in 2 days. Our site has followup counts until the activity is stable, and calculates "uptake" at that point. Then assigns exposure based upon the results (including the "intake" for time present)
There is a diff between intake and uptake - discussion in other posts.

[wlrun3@aol.com]

"On December 16, 2011, you submitted the following question to our Ask the Experts feature: Once an intake is quantified in pCi at a commercial nuclear power plant body counter, how is the dose calculated?

First one has to estimate the intake using appropriate models and Intake Retention Factors (IRFs), see HPJ 83:594 –789; 2002. Then publications like ICRP 30, 60 and others have factors of committed dose per unit intake (Sv./Bq.)."

Once fast scan quantification stabilizes dose is calculated and assigned.

If there was no external contamination, was this a personnel contamination event?

What would the calculation of assigned dose look like referencing Intake Retention Factors?

Given current technology LLD, what is typically the lowest assigned dose in the commercial nuclear power industry?