[ RadSafe ] Dose conversion in beta exposure readings at Fukushima Daiichi ?

[Jaro Franta]

Tepco's latest analysis results:

Aug 23, 2013 - Sampling Results Regarding the Water Leak at a Tank in the H4
area in Fukushima Daiichi Nuclear Power Station

http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/south_discharge
_130823-1e.pdf 

....where the "All beta" numbers are much closer to the Cs numbers -
suggesting but not confirming that the 80kBq/cc in the leaked water from
tank no.5 is largely tritium (these latest results sample nearby "drainage
channel B", not the water from the tank..)


 Jaro
^^^^^^^^^^^^^^^^^^^^^^^^^



-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Jaro Franta
Sent: August-22-13 9:41 AM
To: 'The International Radiation Protection (Health Physics) Mailing List'
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at
Fukushima Daiichi ?

A search on Tepco’s web site turned up this reference document:

Radiation Monitoring at the site - measuring method  (November 19, 2011)
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111119_04-e.pdf

Some of the more interesting slides:

Slide 7:  Estimation of Sv/h from Bq/cm2

Quote: “In the case of Cs-137 contamination radius (40cm), Distance (1m):
13,000cpm = approx. 0.04 Sv/h”


.presumably this conversion applies only to gamma ?
(...yet in their table published this week, they report beta + gamma dose
rates of ~100 mSv/h, with only a tiny fraction of that being gamma)


Slide 9: Radiation Meter for contamination measurement (GM Survey Meter)
Slide 11: External exposure evaluation measure Slide 15: Beta nuclide
measurement (Tritium)


Tepco report slide:
http://db.tt/UfPU1FpJ


 Jaro
^^^^^^^^^^^^^^^^^^^^^^^^^



-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Jaro Franta
Sent: August-21-13 2:57 PM
To: 'The International Radiation Protection (Health Physics) Mailing List'
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at
Fukushima Daiichi ?

Thanks Jim,

Its important to get to the bottom of this bizarre dose rate reporting.

Here's why: According to Reuters,

“Water in the latest leak is so contaminated that a person standing close to
it for an hour would receive five times the annual recommended limit for
nuclear workers.”

http://www.reuters.com/article/2013/08/21/us-japan-fukushima-severity-idUSBR
E97K02B20130821

......how on earth does one get "five times the annual recommended limit for
nuclear workers" from an external beta dose ?
......and how does one even calculate a dose rate in mSv/h from an
instrument reading of beta radiation in the environment ?

Jaro in Wonderland





From: Jim Hardeman [mailto:jim.hardeman at gmail.com]
Sent: August-21-13 10:49 AM
To: jaro_10kbq at videotron.ca
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at
Fukushima Daiichi ?

Jaro --
 
My GUESS is that what TEPCO is talking about isn't an actually dose rate
MEASUREMENT, but a dose rate ESTIMATE performed with some sort of GM tube /
counter with a removable beta shield -- something like the old HP-270 "hot
dog probe". Seems to me that they're simply reporting open window readings
as "beta + gamma" and closed window readings as "gamma". I doubt they're
doing much in the way of making beta dose rate conversions.
 
My $0.02 (US -- don't know what that is these days in Canadian)
 
Jim Hardeman
jim.hardeman at gmail.com





On Wed, Aug 21, 2013 at 10:35 AM, Jaro Franta <jaro_10kbq at videotron.ca>
wrote:
Here's a question about exposure/dose rate numbers reported by Tepco at the
FD contaminated water storage tank farm earlier this week.

A picture from Tepco's pdf document is linked below.

Of interest are the sample analysis results for "Leakage water" in the table
at bottom left, reported in Bq/cm3:  Note especially the "All beta" figure
of 8.0E+4 figure.

The curious part is the table at right, which lists dose rates at various
points around the site in mSv/h - for either "beta + gamma" or gamma alone:
the highest number being ">100 mSv/h" for "beta + gamma" at point #1, and
similar values for points 10, 11, and 12.

My question is how does one apply dose conversion factors to instrument
readings, to derive "beta + gamma" dose rates in mSv/h ? ..which look to be
mostly beta, if one deducts the gamma-only number in the right column.

This is clearly not a case of committed dose due to radionuclides absorbed
in the body. So what is it ? ..if its simply a conversion of instrument beta
particle count rate, what sort of conversion factor would one apply to betas
from tritium, to get mSv/h ?

And although its not explicitly stated, the activity numbers in the lower
table suggest that much of the 8.0E+4 Bq/cm3 activity is tritium, with very
low beta energy (this water was used for cooling the damaged reactors, and
circulated in a closed loop through filters that remove much of the fission
products, but not the tritium..)


Tepco report slide:
http://db.tt/UfPU1FpJ

Thanks

Jaro
^^^^^^^^^^^^^^^^^^^^^^^^^^^