Re: A Question for Power Reactor Types

[hayden_mercer@BELLSOUTH.NET]

Chris,

I started to respond  to your posting and took a power hit.  I may have a

partial reply floating around somewhere.

I am an ex-power reactor type and portal monitors fell into my realm of

responsibility.  Over the years, we have seen a significant increase in the

number of stress tests in our work force and these stress tests do set off

portal monitors, each and every time Tc-99m and/or Tl-201 are used.



Portal monitors typically used in nuclear power plants consist of multiple

plastic scintillation detectors.  The photon energy range runs from 50 kev -

2,000 kev.  Both Tc-99m and Tl-201 have photons in the detection range.

Reliable detection levels are typically in the range of 30 - 50 nanocuries

for Co-60.

Cardiolite seems to be the preferred testing material and the quantity seeme

to run from 10 to 50 millicuries per test.  From personal experience, I

received a Cardiolite test containing 40 millicuries in 1999.  The test was

performed at 9:00 AM.  I went to work about noon.  There are 4 portal

monitors in our security building.  I lit them all before I could even enter

the building.  Direct radiation readings over my kidneys, bladder and liver

ranged from 5 - 10 mR/hr.



Workers are given "passes" to exit the plant without using the portal

monitors.  Clearance time for a worker to pass through the monitor without

initiating an alarm is usually 4 - 7 days, depending on the quantity of

Tc-99m intitally administered.  For tests that involve the administration of

Tl-201, the clearance time to pass through the monitor without initiating an

alarm is around 60 - 75 days. The Tl-202 impurity in the testing material is

responsible for the much longer clearance time than would be expected from

Tl-201 alone.



I think that the "setting of alarms" is only a matter of perspective - kind

of like which side of the fence are you on.  In the medical arena, it takes

a certain quantity of a radionuclide in order to obtain the results a

physician wants.  In the diagnostic arena, the dose to the patient is small

and the benefit to the patient is large.  In the power reactor world, there

is no benefit to the removal of radioactive material from the restricted

area.  In fact, regulations do not allow for the unrestricted release of any

radioactive material.  Hence the low portal monitor alarm setpoints.  The

difference is about a factor of 1.0 E +06, give or take a decade or two.



Doc







 ----- Original Message ----- 

From: <alstonchris@netscape.net>

To: <radsafe@list.vanderbilt.edu>

Sent: Friday, April 16, 2004 11:01 AM

Subject: RE: A Question for Power Reactor Types





> I hope this isn't a reiteration, but it's not in my "Sent" file.

>

>

> >At a hospital where I worked during the mid-90's, we figured that we

saved ~US$1200 per day, when we could rule out a myocardial infarction (MI)

as the cause of chest pain, in the ER, without admitting the pt. Note

though, that it's effectively a stress test, so you're using Tc-99m (say, as

Cardiolite), not Tl-201 (at least that I've ever heard).

> >

> >Also, they're starting to use Tl-201 for oncologic scans now. That goes

along with John's observation about the aging population.

> >

> >I find it *really* hard to believe that anyone's getting enough moly

breakthrough in a tech dose to give photon flux rates that set off portal

monitors.  Plus, the phenomenon would have to be very widespread, wouldn't

it?

> >

> >It's more likely that the pts were given more than one

radiopharmaceutical, the classic example (again) being cardiac studies in

which the pt gets thallium for the resting phase, and tech-99m for the

stressed phase.

> >

> >I await the slings and arrows

> >Cheerio

> >cja

>

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