NuFuel & MMSNF 2015

First Workshop on Research into Nuclear Fuel in Europe
and Materials Modeling and Simulation for Nuclear Fuels Workshop
Karlsruhe, Germany, November 16th to 18th, 2015

Updated: Tue 08 Dec 2015, 14:27

Poster 4.4: Thermodynamic study on the speciation of CsI in nuclear fuel

Joaquina Zappey, O. Benes, V. Tyrpekl, J-Y Colle, R.J.M Konings
  • European Commission, Joint Research Centre, Institute for Transuranium Elements (ITU), Hermann-von-Helmholtz Platz 1, PO Box 2340, DE–76125 Karlsruhe, Germany


The existence of CsI in nuclear fuel pellets has been one of debate. Cs and I and formed in a ratio of 10 to 1 during irradiation. According to thermodynamic studies CsI should be the most stable form of I present under the conditions that prevail during irradiation. However, up to date there is no clear experimental evidence to support the existence of CsI in nuclear fuel.

It is generally accepted that I does not exists in it elemental form in nuclear fuel. If Iodine exist in its elemental form, then it would exhibit similar behaviour to that of the noble gasses. Two arguments proves this not to be true. First, Iodine shows a different release during Knudsen cell experiment compared to noble gasses. Secondly, it does not migrate into the plenum region like the noble gasses do [1]. In addition, several arguments speak in favour of CsI a.o.: Thermodynamic studies show CsI to be the most stable form. X-ray fluorescences of Cs and I deposits on the internal cladding surfaces of commercial irradiated fuel rods has been found. And lastly, Cs and I show the same behaviour during iodine spike phenomena[2].

In this study, we aim to find a decisive answer to the existence of CsI. We do that by performing Knudsen-cell experiments on pure CsI, spark plasma sintered UO2-CsI (SPS-CsI) both stoichiometric and oxidised and compare the data to data from irradiated fuel. Would I be present as CsI in the fuel pellet than its release behaviour and diffraction pattern, would be similar to that of pure CsI and to that of SPS-CsI.

Preliminary results show that CsI might be present in the form of CsI. The ratios between the (Cs+)/(I+),(Cs+)/(CsI+) and (CsI+)/(I+) +peaks in the stoichiometric SPS-CsI sample are found to be similar to the ratios for irradiated fuel samples. This gives us the impression that CsI might be present in the form of CsI. In order to get full discloser more analysis on different irradiated fuel samples will be done.

  1. Davies, J., R. Boyle, and J. Hanus, FISSION PRODUCT AND PLUTONIUM REDISTRIBUTION IN HIGH PERFORMANCE UO2 FUEL RODS. 1966, General Electric Co., San Jose, Calif. Atomic Power Equipment Dept.
  2. Campbell, D., A. Malinauskas, and W. Stratton, The chemical behavior of fission product iodine in light water reactor accidents. Nuclear Technology, 1981. 53(2): p. 111–119.