Career Path > Radiation Safety
Alpha to Beta/Gamma ratio
wiesner1:
Hi--I am looking for some clarification. Why is the alpha:beta/gamma ratio important? Specifically, why is this ratio used in the new EPRI alpha monitoring guidelines instead of simply using alpha contamination levels to determine controls. I have yet to get a good answer on this.
It seems to me that the ratio is important in predicting what alpha levels might be based on the amount of beta/gamma. I can see that. I can see it for predicting intakes of alpha if you know what the beta/gamma ratio is. But I don't get the controls part that of the "Level 1, 2, 3" classification. Concerning beta/gamma decay on lets say, some piece of equipment that has both alpha and beta/gamma contamination--why would my controls increase simply because the beta/gamma has decayed away. The same amount of alpha is present; it has not increased. Why would I use stricter controls just because the beta gamma has decayed away and the alpha level is the same as it always was.
Thanks for any clarification.
hamsamich:
We discussed this at the last plant I was at that has more Alpha 3 areas than most plants and the EPRI guidelines aren't perfect is what we came up with. Nobody had a better answer than that as far as I can see. Plants that have very little alpha probably won't even know what you are talking about. If I remember correctly alpha had to be at least 200 or 2000 (can't remember which) no matter what the ratio was for the stricter controls to be implemented. They actually had a different control that should almost be called "alpha 4" when the ratio goes lower than 50. I don't know if that was in the EPRI guidelines but no matter what the ratio was you always had to have at least 200 or 2000 dpm alpha. Sorry I can't tell you more but some of the supervisors at my last plant did discuss what you are referring to. So for the stricter control you would have to have a ratio below 50 AND at least 200/2000 dpm. Seems to me 200/2000 dpm by itself should be high enough if 50 and 200/2000 is. It has to do with the sensitivity of dealing with Alpha in an industry where it isn't the normal focus maybe. .02$
bigred:
I DONT THINK GETTING MORE STRICT WOULD BENEFIT THEN. -K
GLW:
--- Quote from: wiesner1 on Jul 10, 2014, 10:57 ---Hi--I am looking for some clarification.....
--- End quote ---
Ratios between beta-gamma and alpha are significant to derived dose.
Here's a good read:
http://pbadupws.nrc.gov/docs/ML0833/ML083300646.pdf
It is 57 pages long, so take a couple of hours to digest it, take reference notes, and between the linked paper and the nine references in the linked paper you will understand and you will have your good answer.
Enjoy.
almost forgot - provided we are looking for a good answer within an operating nuclear power plant
Piggyback Beta:
"Concerning beta/gamma decay on lets say, some piece of equipment that has both alpha and beta/gamma contamination--why would my controls increase simply because the beta/gamma has decayed away. The same amount of alpha is present; it has not increased."
Ingrowth. If fission products are present, the cobalt 60 goes away, and the Pu-238, and Pu 240 increases. Pu-241 (14 year half life) feeds the Am-241. Look at Table B-2 in the new guidelines for clarification
With low beta/gamma the tendency is to decrease controls, which can fool the HP. The controls should either stay the same or increase. Old 'level 3' plants with high alpha have very high airborne levels for alpha. The particle size will decrease due to recoil making it harder to control with ventilation and other 'normal' controls.
Some of the 1970's plants are just reaching the point of ingrowth on abandoned systems.
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