NukeWorker Forum
Reference, Questions and Help => Nuke Q&A => Topic started by: guiazevedo100 on Aug 20, 2007, 11:06
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Hi, I'm still a student and I'm doing an internship on the nuclear field. I've found this site really cool and I was wondering if anyone here could help me with a couple of questions:
1. What are the main contamination particles in the steam that goes to the turbine, when in a BWR cycle? If you know some docs where I can find that information it would be great!
2. How many people work in average in an outage for a BWR?
3. The maximun regulation dose for exposure of a worker, is 100mSv in 5 years. Could anyone tell me how much is the average effective dose contamination in practice?
Thanks! Hope someone can help me with my report ! ::)
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average effective dose contamination in practice?
Welcome to NukeWorker. ;D
Many of your questions can be found by using the search function on the site, as I'm sure many of these things have been covered.
Not sure what your asking for with the quoted question, do you mean what is the average dose received by a worker?
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I wanted to know if in reality, the average radiation exposure of workers is around 20mSv (like the regulation allows), or if it is lower than that. Hope to have been more clear this time. And as for the search, I'll keep looking for my answers with it! :)
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What regulation are you referring to?
RE: average dose, that varies widely based on where in the plant the worker is assigned. Likewise, the contaminants in the turbine varie with a number of factors, probably the most important variable being the history of fuel leakage.
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3. The maximun regulation dose for exposure of a worker, is 100mSv in 5 years. Could anyone tell me how much is the average effective dose contamination in practice?
Not sure where you got that number, but the regulatory limit for exposure (combined external and internal) is 50 mSv/year (5 REM) but nobody gets anywhere near that (anymore.) The average used of about 200 mRem/yr (2 mSv) is a little bit of a statistical trick because it includes a lot of people that get virtually no exposure but have a TLD badge and are therefore included in the 'average.' And by average do you want the 'mean,' the 'median' or the 'mode?' Do you include all badged personnel or only those that receive 'some' exposure? Is there a lower limit cut off? What is it?
Very nebulous question, grasshopper.
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I'm not 100% sure. I know when the turbine was disassembled we had to dress out to be on the platform but I;m not aware what the Contamination levels really were. I can tell you I had been doused with Condensate a few times when I was at Fermi and I never got crapped up.
So far as Dose the average Operator there got less than the Average Operator at Sequoyah gets. In a Non Outage year it was extremely low. I was a Non Licensed Operator there for two outages and Approximately 2 and a half years and my total dose was around 800 mr.
At the time we did High Rad Rounds every month and area like the Feed Pumps and Condensate Bay were accessible so we probably picked up more dose doing rounds then. After HWC started many areas we used to physically inspect were changed to looking into a camera.
Mike
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The largest contributor to steam line radiation at a BWR is N-16. This is a neutron activation product and is extremely short lived. We limit access to Steam Tunnels, Turbines, and Feedwater Heaters to minimize exposure from this nuclide. Once we shutdown, N-16 decays away in a minute or so.
If a plant has cladding pinhole leaks, you'll see some Noble Gas activity in the steam lines. Kr-88, and Xe-133 are the big guys here. The fuel reliability engineers can use short lived / long lived Noble Gas activity ratios to determine the size of a cladding defect. These Noble Gases end up decaying away in Charcoal Adsorbers located in the Off Gas System.
Most BWRs are pretty clean plants, the indicator to look at is Reactor Coolant Dose Equivalent Iodine activity. Many plants are near zero, the ones that are not have - or have had- fuel cladding defects.
Hope that helped.
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Contamination levels on BWR steam side components are low. I saw in the 2000 dpm per 100 cm2 range at an outage at Browns Ferry. Secondary rad levels were almost uniformly <1 mrem / hour shortly after shutdown. Only a couple of spots had higher than that.
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The largest contributor to steam line radiation at a BWR is N-16. This is a neutron activation product and is extremely short lived. We limit access to Steam Tunnels, Turbines, and Feedwater Heaters to minimize exposure from this nuclide. Once we shutdown, N-16 decays away in a minute or so.
If a plant has cladding pinhole leaks, you'll see some Noble Gas activity in the steam lines. Kr-88, and Xe-133 are the big guys here. The fuel reliability engineers can use short lived / long lived Noble Gas activity ratios to determine the size of a cladding defect. These Noble Gases end up decaying away in Charcoal Adsorbers located in the Off Gas System.
Most BWRs are pretty clean plants, the indicator to look at is Reactor Coolant Dose Equivalent Iodine activity. Many plants are near zero, the ones that are not have - or have had- fuel cladding defects.
Hope that helped.
YOu touch on a subject I'm researching... effects throughout the plant due to fuel failure. Can you PM me with specifics, history, notes, data, etc?
thanks