[ RadSafe ] Skyshine measurements

[Victor Anderson]

Mattias,

Skyshine from the turbine building is an old problem.  The best software for
modeling skyshine is the MCNP code from Los Alamos.  Low clouds will give
you more scatter because of increased moisture and other stuff in the
clouds.  The major problem will be that "low clouds" are not uniform in
composition or height.  If your plant has the Swedish equivalent of the
Updated Safety Analysis Report, the original calculation and its assumptions
should be available.  This will help to take measurements in conditions
similar to the original calculations.  Generally measurements are made using
the most sensitive TLD chips that you find.  High Pressure ion chambers such
as Reuter-Stokes can be used.  The source of gammas is the N-16 decay
radiations. TLD and pressurized ion chambers will give you a good response
to N-16 radiation.  However, increased dose rates outside of the turbine
building are in the 1e-2 microSieverts/hr range and lower at the site
boundary.  I would suggest making measurements with different cloud
conditions, unless you can control the weather.  :) (In which case, you are
in the wrong business. GRIN).  As far as I know there is no standard
practice as each power plant is different.  The major issue is being able to
demonstrate that the off-site dose limits are being met.

Victor Anderson, CHP

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Olsson Mattias
:MSO
Sent: Wednesday, March 06, 2013 7:33 AM
To: The International Radiation Protection (Health Physics) MailingList
Subject: [ RadSafe ] Skyshine measurements

Hi all,

One BWR plant is to do a power uprate to 120% of the original effect.
During the testing period there will be dose rate measurements in
selected places around  the plant to observe changes in skyshine from
the steam lines in the turbine building. In the documentation it says
that the measurements should be done during weather with "low clouds".
This is supposedly because low clouds will give you a conservative
measurement. There is no source given and I don't have the necessary
software to make a model of it. So what I want to ask is if any of you
could say if it is obviously conservative to measure skyshine with low
clouds (compared to high clouds or sunny weather) and if there is some
standard practice for skyshine measurements around nuclear plants. Being
a humble chemist, it's not obvious to me, although it seems reasonable
that clouds could cause more scattering.

All the best,

Mattias Olsson
Forsmark, Sweden 

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