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Offline fred

posting off of beta dose rates
« on: Sep 17, 2012, 07:51 »
Why is it that Beta dose rates are for the most part ignored? I have seen instances where Id have > a rad in beta but the house or whoever would not want it posted. Also items being removed from the pool and only telepole utilized for dose rates. I understand the basics, but why is Beta dissmised all the time? Ive tried looking through writen material and Im unable to find an answer. Ive always wonderd, wtf. Not talkin about smearable. Maybe someone could help me understand this question which has eluded me all these years.

Offline Already Gone

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Re: posting off of beta dose rates
« Reply #1 on: Sep 17, 2012, 08:02 »
Usually it is because the beta exposure rate is not high enough in proportion to the gamma rate to result in it causing the limiting dose rate.  The ratio of beta/gamma in most power plants leaves the gamma dose rate as your biggest concern.  Overall, even in high beta dose rates, the SDE, or LDE won't be exceeded before the DDE.

Get to DOE or a commercial manufacturing facility ant that won't always be the case.  Pure beta emitters are rare in the power house, but much more common elsewhere.
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Chimera

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Re: posting off of beta dose rates
« Reply #2 on: Sep 17, 2012, 08:59 »
Beta tends to get "ignored" because it's considered to be an external hazard only (skin dose) and usually much less than the gamma readings - as already mentioned.  If the beta is extremely high or poses a risk to the lens of the eye, then you will some sort of compensatory action such as aluminum plates under the lead blankets in the upper channel head of once-through steam generators (aaaah, the old days) or safety glasses when working on things coming out of the fuel pool, valve internals or pump seals.  The relatively short range of power-house betas in air - in the range of 3 to 4 feet - also tends to add to the perception that they don't present any immediate danger to the workers unless the lens of the eye is directly involved.

surf50

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Re: posting off of beta dose rates
« Reply #3 on: Sep 17, 2012, 09:07 »
Back in the day we used to have to wear yellow safety glasses under our bubblehoods when working near/in the s/g channelheads (and for pool work), then a lot of studies were done by folks far above my pay grade who decided the beta was not a risk factor due to the beta/gamma ratio.
And I'm sure you're wearing your safety glasses, right?  ;)



Offline OldHP

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Re: posting off of beta dose rates
« Reply #4 on: Sep 17, 2012, 10:40 »
Why is it that Beta dose rates are for the most part ignored? I have seen instances where Id have > a rad in beta but the house or whoever would not want it posted. Also items being removed from the pool and only telepole utilized for dose rates. I understand the basics, but why is Beta dissmised all the time? Ive tried looking through writen material and Im unable to find an answer. Ive always wonderd, wtf. Not talkin about smearable. Maybe someone could help me understand this question which has eluded me all these years. 

Thanks Already! But most of the time, not always, but the dose would be from items coming out of the pool. The Beta was roughly twice that of games. Anyway, whenever Ive seen high beta > than gamma, enough to warrant a posting change, its been dismissed. Also none seems to survey for beta. I'm not trying to be anal, I just want to understand why Beta is so often dismissed. That and I'm bored. 

Think DDE vs Limit, LDE vs Limit, and SDE vs Limit.  Postings (in most cases) are based on DDE (whole body exposure) and refer to gamma (not games) radiation.  RWP/SWP requirements generally deal with special cases, i.e., high beta (particularly high energy [Sr-90] beta), e.g., eye protection and/or skin protection!
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Offline SloGlo

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Re: posting off of beta dose rates
« Reply #5 on: Sep 17, 2012, 11:28 »
Think DDE vs Limit, LDE vs Limit, and SDE vs Limit.  Postings (in most cases) are based on DDE (whole body exposure) and refer to gamma (not games) radiation.  RWP/SWP requirements generally deal with special cases, i.e., high beta (particularly high energy [Sr-90] beta), e.g., eye protection and/or skin protection!
games should be read as gammies, or gammys, or gammees.  

please note that aye did not say that it should be red as gammies, or gammys, or gammees.
« Last Edit: Sep 17, 2012, 11:29 by SloGlo »
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Chimera

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Re: posting off of beta dose rates
« Reply #6 on: Sep 19, 2012, 12:05 »
games should be read as gammies, or gammys, or gammees.  

please note that aye did not say that it should be red as gammies, or gammys, or gammees.

OMG - SloGlo translating himself for the masses.  Isn't this a glorious age we live in?   ;)

Offline RDTroja

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Re: posting off of beta dose rates
« Reply #7 on: Sep 22, 2012, 07:23 »
Given that:

From 10CFR Part 20 - STANDARDS FOR PROTECTION AGAINST RADIATION

Quote
High radiation area means an area, accessible to individuals, in which radiation levels from radiation sources external to the body could result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in 1 hour at 30 centimeters from the radiation source or 30 centimeters from any surface that the radiation penetrates.

And

Quote
Dose equivalent (HT) means the product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. The units of dose equivalent are the rem and sievert (Sv).

And

Quote
Lens dose equivalent (LDE) applies to the external exposure of the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 centimeter (300 mg/cm2).

And

Quote
(b) Posting of high radiation areas. The licensee shall post each high radiation area with a conspicuous sign or signs bearing the radiation symbol and the words "CAUTION, HIGH RADIATION AREA" or "DANGER, HIGH RADIATION AREA."

You would have to show that the beta dose rate was sufficient to cause > 100mRem/hr at a depth of 0.3 centimeter (surprising because skin dose is .007 centimeters) in order to require a posting change. So, get a 300mg/cm2 absorber and see how much beta you get through it. That would be your Lens Effective Dose and determine if a posting change is required. With 125 mRad/hr in air I am guessing (and it is a guess) that you will probably be below 100 mRem Lens Effective Dose. Now, add in the gamma (which you didn't give) and you may then be above. But you have to get the 0.3cm dose to know for sure.

When talking about Rem-level Dose Rates, with little gamma contribution, you have a real potential for violation if the area is not posted for Beta. Personally I have seen High Rad areas posted for Beta, but is has been rare.
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Offline tolstoy

Re: posting off of beta dose rates
« Reply #8 on: Sep 22, 2012, 07:26 »
10CFR20, definitions, defines a HRA in relation to 'dose equivalent': ie, Sv or R. I think a good explanation was given above that beta dose is in most cased tabulated as skin dose, not whole body. In the same section you see a VHRA defined in relation to Rad or Gy because the conversion to equivalent dose is a qualitative conversion - gamma and beta = 1, etc.

Offline Already Gone

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Re: posting off of beta dose rates
« Reply #9 on: Sep 22, 2012, 07:30 »
Based on the 10CFR20.1003 definition of a High Radiation Area,
"High radiation area means an area, accessible to individuals, in which radiation levels from radiation sources external to the body could result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in 1 hour at 30 centimeters from the radiation source or 30 centimeters from any surface that the radiation penetrates." and the definition of dose equivalent,
 "Dose equivalent (HT) means the product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. The units of dose equivalent are the rem and sievert (Sv).",
I would post that as a High Radiation Area.
The HRA definition makes no distinction between the various types of dose equivalents.  Since the LDE and SDE, are (by definiton) dose equivalents, and the exposure rate at 1 cm is >100 mRad/hr @ 30cm, and that would result in a DE greater than 100 mRem in one hour, I'd say post it.
I am basing that on your info, and the assumption that when you say "125 mRad", you mean 125 mRad/hr of combined beta and gamma dose rate calculated as ((OW-CW) x BCF) + CW = 125 Mrad/hr.
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Offline RDTroja

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Re: posting off of beta dose rates
« Reply #10 on: Sep 22, 2012, 07:43 »
In formatting my previous post, I managed to remove the part about skin vs. eye dose. Skin dose would be more limiting for dose rates with its .007 cm depth (.7 mg/cm2 but I originally had a disclaimer that the organ of greater concern was the lens of the eye and that was the basis for what I wrote. For posting purposes the skin dose is more limiting. For exposures, the lens of the eye is.
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Offline OldHP

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Re: posting off of beta dose rates
« Reply #11 on: Sep 22, 2012, 09:57 »
You guys are great. Thank you for the deep thoughts on this. Its not as simple as it would seem. I would be conservative and post HRA. But..... What would we be legally required to do? I wish NRC would chime in. Ive been doing this "RP" for a long time, but Ive never been given an answer or come to a conclusion. Once again , tanks

You have to understand the definitions and meanings given above.  You may have been doing "this RP" for a long time, but I'd venture several of the posters were doing it before you were born.

As RDT said, I have posted or had posted an area as a HRA based on the beta, however outside of a lab environment that is very rare.  Your example just listed OW meter readings. Postings are based, today, on DE!
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Offline retired nuke

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Re: posting off of beta dose rates
« Reply #12 on: Sep 23, 2012, 10:06 »
Per 10CFR20, posting limits are based upon the dose rate at 30 cm. Beta is usually NOT a significant part of the overall dose rate at that distance.
From http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1003.html:

Radiation area means an area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 0.005 rem (0.05 mSv) in 1 hour at 30 centimeters from the radiation source or from any surface that the radiation penetrates.

High radiation area means an area, accessible to individuals, in which radiation levels from radiation sources external to the body could result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in 1 hour at 30 centimeters from the radiation source or 30 centimeters from any surface that the radiation penetrates.

Each plant / site / utility / licensee writes procedures to ensure that they comply with NRC regulations. Each of them may do it a different way,and may exceed the regs to some degree. But those procedures are reviewed as part of the periodic NRC inspections. I have had discussions with NRC inspectors regarding the procedures at different sites I have worked at. NRC only cares that you meet the regs.

You may also see in further reading of the regs, that an HRA must be locked. How does the power generation industry get away from not locking HRAs? Because we have Tech Specs - our license. It allows us to take credit for training, and make our locking point at 1 rem/hr vs 0.1 rem/hr. Places like hospitals and labs may not have that clause in their license.

So - if your beta reading at 30 cm meets the posting requirements - then by all means post - unless the station tech specs don't require it. Most power plants beta energy won't climb that far.....
The basement of ANO1 ctmt may be an outlier... :D

Thanks for the question, and the interesting discussion.  ;)
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Offline spentfuel

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Re: posting off of beta dose rates
« Reply #13 on: Sep 24, 2012, 12:17 »
Posting requirements are based on DDE only (gamma + neutron).  The question came up in reference to the definition of a very high rad area at 500 rads/hour at 1 meter.  When the new part 20 was coming out in 92 the NRC hosted a Q&A site and provided HP position paper (HPPS) stating very clearly that posting was driven by DDE only.  The utility folks asked the question "then why use rads instead of rem"  The NRC reply was simply at very high doses rads are appropriate.

Don't have much time to look up the Q&A or HPPS that explains this but knock your self out if you do.

BTW if you have beta dose rates at twice your gamma that's not high its low.  Its not uncommon to see beta dose rates at 10 to 20 times gamma when dealing with primary system components at a Nuke plant.

So you may want to consider bagging some beta's to add to your fuel pool since you seem so low  :D

my two cents

sf

Chimera

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Re: posting off of beta dose rates
« Reply #14 on: Sep 24, 2012, 12:41 »
Theres no reason to get s@#$ty. I was born in 67 and am asking a valid question. Are we required to post an area on beta dose rates that are > bkd gamma dose rates from a legalities stand point. Its a simple question but one Ive never gotten an answer to. Theres no stupid questions, ........
Edited for profanity

You've been given the answer over and over again.  That you don't like it because it doesn't conform to what you appaarently want to hear is obvious.

As to the use of Rad for Very High Radiation Areas versus rem for the lower postings, you need to review stochastic and non-stochastic dose - probabilities versus measurable results.

 


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