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RE: Procedures for detecting and characterising hot particles
Mr. Charles,
I unearthed an old document that I developed an eon ago and cut a few
paragraphs out. Here's the cut:
The two principle types and origins of hot particles are:
1) IRRADIATED FUEL FRAGMENTS (IFF) OR FLEAS
Tiny specks of highly radioactive spent fuel, which has escaped from holes
in the fuel cladding.
2) ACTIVATION (COBALT) PARTICLES
Tiny slivers of highly radioactive metal, which have been activated in the
core.
Fleas originate from irradiated fuel pellets. They escape the fuel cladding
when cladding failures occur. Failure to thoroughly dry fuel rods during
fabrication can leave excess moisture inside the fuel rods. During power
operation this water becomes a source of hydrogen, which reacts with the
zirconium cladding. Primary hydriding embrittles and corrodes the cladding
from the inside out, resulting in small holes in the fuel pins.
Water enters primary holes promoting secondary hydriding. Fluctuating power
levels speeds up the process by creating pressure and temperature
differentials between the inside and outside of the fuel pin.
Cobalt particles are wear products or metal slivers which have been
activated in the core. Cobalt particles can originate from activated core
internals as wear products such as stellite bearings which are high in
stable cobalt-59 but are most likely to originate outside the core and be
activated ((Co-59(n,gamma)Co-60)) when passing through the core during
operations.
Other types of hot particles are also possible including pure cerium, pure
ruthenium, and pure antimony particles.
High beta energy levels allow fleas to be uniquely identified using gross
counting instruments. fuel fleas are identified by the abundance of fission
products using gamma spectral analysis
PREDOMINANT GAMMA EMITTING FISSION PRODUCTS - OLD FLEA
* cerium/praeseodymium-144
* ruthenium/rhodium-106
PREDOMINANT GAMMA EMITTING FISSION PRODUCTS - NEW FLEA
* zircomnium/niobium-95
* barium/lanthenum-140
* cerium-141
PREDOMINANT RADIONUCLIDES NOT DETECTED BY GAMMA SPEC
* promethium -147 (beta only)
* strontium/yttrium-90 (beta only)
* curium-242 and curium-244 (alpha only)
* plutonium-238 and plutonium-239 (alpha only)
* americium-241 (alpha only)
NOTE: The abundance of zerconium/niobium-95 and barium/Ianthenium-140 can be
used to determine the age of a fuel flea.
In addition to the presence of any radionuclide above, it is also necessary
to show that the activity is from a discrete particle before a sample is
classified as a hot particle.
HOT PARTICLE IDENTIFICATION - GROSS COUNTING METHODS
The maximum beta energy in fuel fragments is about 3 MeV while the max beta
energy in a cobalt particle is only 0.3 MeV. This large difference in beta
energies helps distinguish between the 2 types of particles.
HOT PARTICLE IDENTIFICATION - GAMMA SPEC
The isotopic composition is highly dependent on the age of the particle out
of the core. Generally for a new flea, there is an inverse relationship
between total activity and half-life for each radionuclide. The most active
atoms (abundant in new fleas) tend to decay away leaving the less active
atoms with longer half-lives. The abundance of short-lived nuclides can
therefore be used to date a flea from the time it was in the core.
FUEL FLEAS - EXCLUSIVELY FISSION PRODUCTS
Fission of U-235 occurs after capturing a thermal neutron. The fission
products or fission fragments that result are radioactive and usually decay
in chains which are several members in length.
Fuel fleas consist of the insoluble fission products, which exclude the
noble gases, iodine, and most of the cesium. Normal activation products such
as Co-58/60 and Fe-59 are present only as contamination.
FUEL FLEAS - TRANSURANICS
The transuranic radionuclides present include unfissioned U234/235/238, as
well, as other transuranic radionuclides, which are produced by nuclear
capture reactions. These other transuranics include curium-242/244,
plutonium-238/239, and americium-241 in order of abundance.
The gross alpha activity of a fuel flea is typically 2 to 3 orders of
magnitude lower than the gross beta activity. On the number of atoms basis,
most of the atoms are uranium-238. It because of its low specific activity
(half-life a 4.5 billion yrs) it is not a significant contributor to the
alpha activity.
Rad-safers, let me know if this is interests you and I will send you the
rest of the story....
Marvin Hadley :)
-----Original Message-----
From: owner-radsafe@list.vanderbilt.edu
[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of MW Charles
Sent: Tuesday, January 15, 2002 1:12 PM
To: radsafe@list.vanderbilt.edu
Subject: Procedures for detecting and characterising hot particles
Dear Colleagues
Hot particles (physically small radioactive sources) are a common
problem on nuclear reactors and reprocessing facilities. As far as I
know there is no standard national or international protocol which
describes the most appropriate methods for their detection and
characterisation (chemical and radioactive composition, activity,
size, mass, etc). I recall some years ago coming across American
reports which went some way towards this. Please can anyone
direct me to appropriate literature or individuals who may be able to
help.
Many thanks
Monty Charles
***********************
Dr Monty Charles, Reader in Radiation Physics
Radiation Biophysics Group
School of Physics & Astronomy
University of Birmingham
Edgbaston
Birmingham B15 2TT
England
TEL +44 0121 414 3483
FAX +44 0121 414 4725
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