[ RadSafe ] Skyshine measurements

Thu Mar 7 00:12:23 CST 2013

Dear Radsafe:

     Hmmmm, interesting stuff.  The N-14 at  reactors (dose equivalent 
rate) is pretty high.  Guess people 
don't spend much time in the turbine room.

     A nuclear plant should be able to afford a  portable MCA, NaI or Ge 
detectors, a few LiI(Eu) detectors
and some NIM electronics.  If there is a machine shop, they could make  
Bonner spheres themselves???
Otherwise, LiI(Eu) detectors and Bonner Spheres are available from  Ludlum.

    NIM electronics are old school these days.  CAMAC  and FASTBUS 
electronics are the newer
electronics modules.  I'm stuck in the NIM electronics, I guess.

    MCNP is up to MCNP4, MCNP5 (or MCNP6???).  It is  available from Los 
Alamos National Lab, or perhaps RSICC (Oak Ridge).  An  MCNP training course 
is sometimes advertised in the Health Physics
Newsletter.  MCNP can be used for neutron and gamma shielding, and  some 
electron problems.
EGS (Electron Gamma Shower) may be useful for some electron shielding  
problems.

   Some articles about neutron and other calibrations are by  Eisenhauer 
and Schwartz and Hunt
(Great Britain).  I'm sure more recent articles are available in  Health 
Physics magazine or elsewhere.

    Regards,  Joe Preisig

PS Bonner Sphere neutron data analysis is a mathematical unfolding (not  
deconvolution) problem.
     The problem is mathematically underdetermined... 7  Bonner detectors 
and 31??? or so energy bins.
      For BON4/BON5, the iterative solution method  is described in 
Patterson and Thomas, and in an
      article by Awschalom.  Routti did work  with LOUHI.  Other unfolding 
codes exist.  BON4/BON5
      solutions are OK, if you do the neutron  calibration properly.  The 
BON4/BON5 graphics software
      is not so wonderful.  You might want to  plot unfolded results by 
hand, or graph the data using
      GRAPHER or some other plotting  software.  MAXED is a neutron 
spectrometry code out  of  EML.
      It requires two passes through the data and  uses advanced 
algorithms.  Questions, just email me.
      I haven't used MAXED and am not currently  doing Bonner spectrometry 
professionally.
      Neutron Spectrometry can be done in the 20  MeV to 400 MeV energy 
range using the plastic
      scintillator activation method described in  the back of Patterson 
and Thomas's book.

In a message dated 3/6/2013 11:58:13 P.M. Eastern Standard Time,  
victor.anderson at frontier.com writes:

Good  Evening,

This is indeed interesting. Perhaps Ted could share some of  his results.
With a BWR, skyshine is a more straight forward issue.   The major radiation
source is N-14 in the steam as it travels through the  turbine.  While
working at Peach Bottom I had the opportunity to  measure dose rates in the
turbine building alongside the turbines at full  power.  As I recall dose
rates were about 1 rem/hr at roughly 2 to 3  meters from the turbine 
surface.
Skyshine is a function of what lies  directly over the turbines.  Most 
plants
will have a thin steel roof  over the turbine deck.  This has more to do 
with
the weather than  anything else.  After the N-16 photons radiate into the 
air
above the  turbine roof, they are subject to scatter.  As someone has 
pointed
out  moisture in the air, air density, etc will determine scattering of the
N-16  photons.  If the turbine building is subject to low lying fog, then  
the
fog could act as thin shield.  A low cloud bank will increase  the
scattering.  How much is an interesting question.  For those  of you with a
masochistic streak, the calculation can be done using a good  monte carlo
code such as MCNP 2.7.0.  In my opinion, the best method  is to make
measurements.  The good news is that you only have to  measure the scattered
N-16 gammas.  The bad news is that dose rates  are very low.  The trick of
using 1 inch (2.54 cm) by 12 inch (30.48  cm) compensated GM tubes is
intriguing.  One big question is how  sensitive these detectors are.  At the
site boundaries, the best  method is to take integrated doses over long
periods of time (e.g.,  months).  One problem that our Swedish friend has is
this requirement  to take measurements at 120% of power and with low laying
clouds.  The  low laying cloud issue is a problem simply because clouds will
not stay  low, maintain the same composition, or even keep the same 
altitude.
What  will be required is a good weather data base. Even then, it will be
hard to  determine what part of the measured rates are due to low  laying
clouds.  One technique could be to measure closer to the  turbine building
where measurable readings can be made.  With some  luck, the influence of 
low
laying clouds may be seen.  In my opinion,  ultimately what counts is the
annual rates at the site boundary.  As  long as measurements show that 
annual
dose rates are well within regulatory  limits, the plant has met standards.

Victor

-----Original  Message-----
From:  radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu]  On Behalf Of Ted de Castro
Sent: Wednesday, March 06, 2013 6:39 PM
To:  The International Radiation Protection (Health Physics) Mailing List
Cc:  JPreisig at aol.com
Subject: Re: [ RadSafe ] Skyshine  measurements

Sounds like lots of very expensive  instrumentation!

I set up an active area monitoring network at Lawrence  Berkeley 
Laboratory many years ago - maybe you were at the San Jose mid  year some 
time ago and heard my paper on it.  My work was basically  an improvement 
on a system started by Lloyd Stephens there in  1963.

In any event - it uses cheaper, simpler and very reliable  
instrumentation to good effect:  A 1 inch dia by 12 inch long energy  
compensated GM and a Hankins Modified, high energy modified moderated  
He3 detector.  The system runs reliably for years on end and is  
sensitive enough to clearly show variations in background radiation - be  
it seasonal or even when its raining!  The system integrates data in  10 
minute intervals - this allows tracking changes with changes in  
accelerator operations - either by comparison to accelerator running  
logs and/or by comparing readings from local instruments with those from  
the perimeter instruments on the network.

Using this I've been able  to characterize things like perimeter 
contributions from the ALS  accelerator during fill as opposed to normal 
running conditions.   Never got around to writing that up as a paper - 
just an internal  note.

These instruments would certainly be able to characterize the  fields 
discussed in this thread under the various conditions mentioned as  a 
temporary set-up and probably even be of use as a permanently installed  
monitoring system (not requiring the high energy neutron configuration -  
of course).

On 3/6/2013 10:40 AM, JPreisig at aol.com wrote:
>  Dear Radsafe,
>   
>       Skyshine  is discussed in Patterson and Thomas's  Accelerator Health
>  Physics and/or
> Cossairt's Course notes on Accelerator Health  Physics.
>   
>       Guess other  Radsafers have commented on the  meteorology of 
skyshine
>  measurements.
>   
>       For field  measurements of Skyshine, perhaps use a  portable MCA
> counting  system with NaI or Ge
> detector, or whatever you have available.   If there is a neutron
> component, you can make flux density
>  spectra measurements with a set of Bonner Spheres and one or two  LiI(Eu)
> detectors.  Hopefully
> reactor neutron and/or  photon/gamma signals are not highly variable in
> time, so you don't  need
> 7 LiI(Eu) detectors, just one or two.  Bonner Spheres  (polyethylene)  are
> fairly expensive.  You can analyze  Bonner data with BON4/BON5,  LOUHI???,
> MAXED??? or other  unfolding codes available from
> RSICC (Radiation Shielding Information  Center at ORNL).  If you end up
> using an Anderson-Braun
>  detector only, maybe you would want to make a set of measurements as a
>  function of angle (measured
> from horizontal) pointed up towards the  sky.
>   
>      Like the other guy said,  you can mathematically model  the problem
> using MCNP (Monte  Carlo
> Neutral Particle Program).  MCNPX can be used for high  energy
> neutron/hadron transport, but that may
> not be necessary  in this case.
>   
>      Have fun.   Regards,  Joseph R.  (Joe) Preisig
>    

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