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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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