Question about Cumulative Fission Yields

1. Nov 28, 2012

mesa

So CFY gives the average number of atoms of a specific nuclide produced from a fission directly plus that from the decay of precursors, so why does thermal U233 have two values for Gallium @ 7.192x10^(-8) and 1.0788x10^(-8)? Is this number dependent on the thermal range the neutrons that hit the nucleus of U233?

2. Nov 28, 2012

Staff: Mentor

What is the source of the data. Some databases will give a cumulative fission yields for thermal and fast fissions, and some give the fast fission yield at ~1 MeV and/or 14 MeV.

Last edited: Nov 28, 2012
3. Nov 28, 2012

mheslep

For this topic the interest is in thermal neutron fission, i.e. a MSR, just like a light water solid fuel reactor.

4. Nov 28, 2012

mesa

Just what mheslep said, we are looking at thermal. I got the values for a parent U233 off of this chart for Gallium 69:
http://www-nds.iaea.org/relnsd/vchart/
I don't understand why there are two values there.

I noticed the IAEA definition for CFY's is, "total number of atoms of a specific nuclide produced directly by a fission event and via decay of precursors", (link:http://www-nds.iaea.org/sgnucdat/safeg2008.pdf) but wikepedia says it is per 100 fissions (link:http://www.nucleonica.net/wiki/index.php/Help:Fission_Products_and_Yields [Broken]), which is correct?

Last edited by a moderator: May 6, 2017
5. Nov 28, 2012

Staff: Mentor

The second value should be the uncertainty. These values are from the European database.

From the JENDL-4.0 database (http://wwwndc.jaea.go.jp/cgi-bin/nuclinfo2010a.cgi?31,72,1) for Ga-72 gives:
Code (Text):
Neutron-induced Fission Yields - Cumulative Fission Yield -
Product  Nuclide  Energy(eV)  Fission Yield  Uncertainty(s)
------------------------------------------------------------
Ga- 69    U-233 (T) 2.53e-02   9.397010e-08   4.234410e-08
Ga- 71    U-233 (T) 2.53e-02   1.617040e-06   7.289880e-07

Ga- 72   U-233 (T) 2.53e-02   4.163520e-06   2.662330e-06
Ga 69, 71 are stable.
I added 69 from (http://wwwndc.jaea.go.jp/cgi-bin/nuclinfo2010a.cgi?31,69,1)
and 71 from (http://wwwndc.jaea.go.jp/cgi-bin/nuclinfo2010a.cgi?31,71,1)

I'd trust the iaea definition, but one should verify with another sources, e.g., US DOE national lab like Brookhaven

LWR have a fast flux. Fast fission accounts for 8 to 10% of fssions in an LWR, although that is in U-238. Likewise, the MSR will have fast fission. The problematic (n,α) reaction in Ni is from fast neutrons; the (n,α) reaction does not occur at thermal energies.

Last edited by a moderator: May 6, 2017
6. Nov 28, 2012

mheslep

Thanks.

Would it? Yes there will be fast neutrons, but there would be no U238 in a Th based MSR to fission from fast neutrons.
http://en.wikipedia.org/wiki/Thorium_fuel_cycle#Actinide_wastes

Last edited: Nov 28, 2012
7. Nov 28, 2012

mesa

Uncertainty, very good.
Those values on your table are slightly different from the table I used, should I stick with iaea values or switch to jaea?