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

Tue Aug 27 13:54:21 CDT 2013

The latest TEPCO handouts include the first I have seen that reports analysis results on tritium.

The data is NOT for the recent water leak around the H-area storage tanks, but nevertheless provides a useful indication of a typical ratio of tritium versus other nuclide activity.
In this case the ratio is about 39.2 relative to Cs137 (using 2000/51 for “North side of Unit 1-4 water intake channel”).

Taking the tank water results published earlier – 100 Bq/cc of Cs137 – and including the 15.8 depletion factor from the Cs stripping process -- the tritium activity should be about 39.2 x 15.8 x 100 = 61,960 Bq/cc.

As noted earlier, total fission product beta based on Sb125 ratio should be 242 x 71 Bq/cc = 17,202 Bq/cc.

Adding 61,960 Bq/cc tritium and 17,202 Bq/cc fission product beta yields 79,163 Bq/cc total beta – virtually identical to the “All ß” figure of 80,000 Bq/cc originally reported for the tank water.

Is it just coincidence that the numbers match ? …seems unlikely.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/2tb-east_13082601-e.pdf

 Jaro
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-----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-26-13 10:34 AM
To: 'The International Radiation Protection (Health Physics) Mailing List'
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at Fukushima Daiichi ?

Thanks Jim,

I am not familiar with conversion factors for deriving skin dose expressed as dose equivalent.

Is there a decent on-line reference somewhere, please ? (PS. I’m not an HP, but judging by the number of responses to my question, that doesn’t seem to make much difference…)

Also, is it normal practice to leave people guessing about what sort of interpretation is the correct one, rather than simply spelling out what it is that’s being published ?

Jaro

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From: Jim Hardeman [mailto:jim.hardeman at gmail.com] 
Sent: August-26-13 10:13 AM
To: jaro_10kbq at videotron.ca
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at Fukushima Daiichi ?

Jaro --

Yeah, I was thinking that Sr-90 and Pu-241 might make a significant contribution.

Looks as if the Japanese were PERHAPS a bit more rigorous in performing their dose estimates than I originally thought. I'm interpreting TEPCO's latest as being (shallow) skin dose expressed as dose equivalent as opposed to organ dose to the skin. Is that your interpretation as well?

Jim

On Mon, Aug 26, 2013 at 9:08 AM, Jaro Franta <jaro_10kbq at videotron.ca> wrote:

Additional instrument info posted by Tepco today:

"Measurement device: Shallow ionization chamber survey meter (AE-133B)"

Also, the same four high dose rate numbers listed previously as "γ+β ray"
are now listed as "Dose equivalent rate measured from 70μm (β ray)"

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_1308 <http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130823_05-e.pdf> 
23_05-e.pdf

 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-23-13 7:53 PM
To: 'The International Radiation Protection (Health Physics) Mailing List'
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at
Fukushima Daiichi ?

Jim, I will save you the time:

Here are the results of SNF decay after 2.49y, obtained using the
SpentFuelExplorer java tool, by K. Sorensen.

One is in pie chart form, the other a table:

https://dl.dropboxusercontent.com/u/11686324/SNF_2%2C49y_old.JPG

https://dl.dropboxusercontent.com/u/11686324/SNF_2%2C49y_old_table.JPG

Cheers,

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

From: Jim Hardeman [mailto:jim.hardeman at gmail.com]
Sent: August-23-13 9:02 AM
To: jaro_10kbq at videotron.ca
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at
Fukushima Daiichi ?

Jaro --

It's unclear to me that what TEPCO calls "all Beta" is tritium -- I think
it's more likely to be a gross beta measurement, which would include both
Cs-134 and Cs-137 and any other non-volatile beta-emitters in the water.
This long after the incident, I'd have to do some decay calculations to see
what I would "expect" to be in the water, but the Cs isotopes, while
certainly the most prominent, aren't the only ones.

Jim

On Fri, Aug 23, 2013 at 8:07 AM, Jaro Franta <jaro_10kbq at videotron.ca>
wrote:
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 <http://www.tepco.co.jp/en/nu/fukushima-np/f1/smp/2013/images/south_discharge_130823-1e.pdf> 
_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 <http://www.reuters.com/article/2013/08/21/us-japan-fukushima-severity-idUSBRE97K02B20130821> 
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
^^^^^^^^^^^^^^^^^^^^^^^^^^^