Re: Alpha Sampling

["MIKE RUSSELL" <russelmj@songs.sce.com>]

Robert Leib wrote:

I am examining the methodology used for determining the alpha sampling
requirements for airborne and surface contamination at the nuclear power
plant where I work.

  Low alpha contamination levels as determined by 10CFR61 waste stream analysis
  is a reasonably good indication of the alpha to beta-gamma ratio at your
  facility.

  By apply the concentrations of each radionuclide to their corresponding ALI's
  you can determine the %ALI contributed by these alpha emitting transuranics
  (and other non-gamma emitters for that matter).

  Although the alpha activity levels are low, their contribution to the total
  ALI fraction can be significant because their ALI's are 1000 to 10,000 times
  more restrictive the your typical beta-gamma emitter.

  There's quite a bit of literature on alpha emitters based on calculated
  concentrations in spent fuel and direct analysis of waste.  John Frazier at
  IT Corporation put together a nice Continuing Education Lecture in the 1988
  HPS Meeting in Boston.  Charles Bradley Mitchell at Brown's Ferry published a
  paper in an NRRPT meeting in Athens, Alabama. In the HPS Journal check out
  the Inhalation Toxicoloy Research Institute paper on monitoring, Vol.54,
  No.5, page 503.

  Concentrations in spent fuel vary considerable from time after discharge.
  Curium-242 is by far the most abundant alpha emitter followed by Cm-244,
  Pu-238, Pu-239 and Am-241.  The beta emitting Pu-241 which is 10 times more
  abundant than all the other transuranics combined but doesn't play a big role
  because of it's ALI.

  You mentioned cerium-141 ratio as a tagging method.  That works pretty good
  for fresh contamination from failed fuel but becomes less reliable with time
  because of the different decay rates.

  You've mentioned volumes and count times as an operational difficulty, 1000
  to 3000 liters is required to see 10% of an effective DAC.  That's a pretty
  long sample time if your using a 2 liter/minute low vol.

  Of course the other difficult is interference from radon and to a less
  degree thoron.  The combined half-life for radon daughters is about 30
  minutes while the half-life for thoron daughters is 10 hours.  Waiting and
  counting is one strategy but if you want immediate results I think the
  angular kinetic impactor (AKI) air sampler is the way to go.  Alpha spec is
  another possibility but more difficult.

  Staplex Air Sampler Division can be reached at 800-221-0822.  They'll send
  you some literature on their AKI.

  Michael J. Russell, CHP
  russelmj@songs.sce.com