THE THERMODYNAMIC
PROPERTIES OF THE
TRANSURANIUM HALIDES
Part I
Neptunium and Plutonium Halides
EUROPEAN COMMISSION
JOINT RESEARCH CENTRE
EUR 17332 EN The mission of ITU is to protect the European citizen against risks associated with the
handling and storage of highly radioactive elements. ITU's prime objectives are to
serve as a reference centre for basic actinide research, to contribute to an effective
safety and safeguards system for the nuclear fuel cycle, and to study technological and
medical applications of transuranium elements.
fu 1' THE THERMODYNAMIC
PROPERTIES OF THE
TRANSURANIUM HALIDES
Part I
Neptunium and Plutonium Halides
M.H. Rand
Wintershill Consultancy, Dry Sandford, Abingdon (United Kingdom)
J. Fuger
Commission of the European Communities
Joint Research Centre
Institute for Transuranium Elements,
Karlsruhe (Germany)
Institute of Radiochemistry (B16),
University of Liège-Sart Tiiman,
Liège (Belgium)
EUROPEAN COMMISSION
JOINT RESEARCH CENTRE 'en "t
Transuranium
Elements
2000 EUR 17332 EN LEGAL NOTICE
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Printed in Italy THE THERMODYNAMIC PROPERTIES OF THE TRANSURANIUM HALIDES
SUMMARY
The thermodynamic data for the actinide halides were most recently reviewed in
1983 by Fuger et al. [83FUG/PAR], with some subsequent updates on the
gaseous halides by Hildenbrand et al. [85HIL/GUR]. The current report has
completely updated these reviews for the halides of neptunium and plutonium in
the following respects:
• The latest experimental data have been incorporated
• The most recent values for all the auxiliary data used (atomic weights,
fundamental constants, temperature scale etc.) have been used.
• The values of the partial molar enthalpies of formation of the hydrogen
halides in their aqueous solutions have been re-evaluated, leading to
minor changes in some of the enthalpies of formation.
• The assessment of the data for Gibbs energies of reaction has been
improved by estimating the heat capacities of all the species involved as a
function of temperature, rather than using a constant value for ACp as in
earlier works.
Tables of the thermal functions and Gibbs energies of formation as a function of
temperature are included for all species for which these data are reasonably well
defined.
Part 2 of this report, in preparation, will deal with the halides of the
transplutonium elements.
References see section 6 CONTENTS
1 INTRODUCTION
2 AUXILIARY DATA 8
2.1 Fundamental Constants 8
2.2 Atomic Weights 8
2.3 Temperature Scale 8
2.4 Pressure Units and Standard State Pressure 8
2.5 Auxiliary Thermodynamic Data 8
3 NEPTUNIUM HALIDES 11
3.1 Neptunium Fluorides 11
3.2m Chlorides 12
3.3m Bromides 22
3.4 Neptunium Iodides 30
3.5ms 34
36 PLUTONIUM HALIDES
36 4.1 Plutonium Fluorides
4.2m Chlorides 36
4.3 Plutonium Bromides 46
56 4.4m Iodides
61 4.5 Plutoniums
63 5 ACKNOWLEDGEMENTS
6 REFERENCES 64
70 APPENDIX
Tables of Thermodynamic Data 70 THE THERMODYNAMIC PROPERTIES OF THE TRANSURANIUM HALIDES
List of Tables
2.1 Auxiliary data for HX acid solutions
2.2 Selected values for AfH(298.15K) of Np and Pu ions at infinite dilution and in HCl
solutions
3.1 Molecular parameters of neptunium halide gaseous species
3.2 Extrapolation of AfH(MF3, cr) - AfH(M+3, aq) vs. ionic radii of M+3
3.3n of AfH(MF4, cr) -+4, aq) vs. ionic radii of M+4
3.4 Enthalpy of sublimation of NpF4(cr)
3.5 Extrapolation of AfH(MF6, cr) - AfH(M02+2, aq) vs. ionic radii of M(VI)
3.6n of AfH(MCl3, cr) - AfH(M+3, aq) vs. ionic radii of M+3
3.7 Extrapolations for the enthalpy of formation of NpOBr2(cr)
4.1 Molecular parameters of plutonium halide gaseous species
4.2 Vapour pressure data for the sublimation of PuF3(cr)
4.3 Extrapolation of AfH(MF4, cr) - AfH(M+4, aq) vs. ionic radii of M+4
4.4 Summary of estimates for AfH(PuF4, cr, 298.15K)
4.5 Fitted vapour pressure parameters for PuFé(cr)
4.6n of AfH(MCl4, cr) - AfH(M+4, aq) vs. ionic radii of M+4
A. 1 Summary of thermodynamic properties
A.2 Thermodynamic properties of individual species
List of Figures
3.1 Pressures of NpF4(g) over NpF4(cr) and Np02F2 (cr)
3.2 Vapour Pressures of NpCLt(cr) and NpCl4 (liq)
4.1r Pressure of PuF3(cr)
4.2r Pressures of PuF3(cr) and PuF4(cr)
4.3 Vapours of PuCl3(cr) and PuCl3(liq)
4.4 Equilibrium Constants for the reaction PuCl3(cr) + 0.5 Cl2(g) = PuCUCg)
4.5r Pressures of PuBr3(cr) and PuBr3(liq) THE THERMODYNAMIC PROPERTIES OF THE TRANSURANIUM HALIDES
1. INTRODUCTION
The thermodynamic data for the actinide halides were most recently reviewed in 1983 by Fuger
et al., [83FUG/PAR], with some subsequent updates on the gaseous halides by Hildenbrand et al.
[85HIL/GUR]. The current report has updated these reviews in the following respects:
• New experimental data have been incorporated.
• The most recent values for all the auxiliary data used (atomic weights, fundamental
constants, temperature scale etc.) have been used, as described in section 2.
• The values of the partial molar enthalpies of formation of the hydrogen halides in their
aqueous solutions have been re-evaluated, leading to minor changes in some of the
enthalpies of formation.
• The consideration of the data for Gibbs energies of reaction has been improved by
estimating the heat capacities of all the species involved as a function of temperature,
rather than using a constant value for AC as in earlier studies
• Revised values of the enthalpies of formation of the aqueous actinide ions, taken from
[2000LEM/FUG] have been used.
The thermal functions for most of the gaseous species were calculated from estimated molecular
parameters and electronic energy levels. Although the resultant data can sometimes be checked
{e.g. by comparison with experimental entropies of vaporisation), they can have appreciable
uncertainties. In general, these have not been included in the stated uncertainties. THE THERMODYNAMIC PROPERTIES OF THE TRANSURANIUM HALIDES
2. AUXILIARY DATA
All the auxiliary data used have been converted to the most recent values, as summarised in the
next sections.
2.1 Fundamental Constants
The 1986 values for the fundamental constants published by COD ATA [86COD] have been
utilised.
2.2 Atomic Weights
The 1991 set of atomic weights published by IUP AC in 1992 [92IUP] was utilised.
2.3 Temperature Scale
Most high temperature measurements considered here are not of sufficient precision to require
conversion, but where noted a few precise vapour pressure studies were converted from the scale
in use at the time of thes (1927, 1948 or 1968), using the conversion tables given by
Goldberg and Weir [92GOL/WEI].
2.4 Pressure Units and Standard State Pressure
Pressures are given in bar (0.1 MPa) units, and the standard state pressure for the entropies and
Gibbs energies of ideal gases is 1 bar.
2.5 Auxiliary Thermodynamic Data
2.5.1 Non-actinide Data
Auxiliary thermodynamic data were taken from the final COD ATA Key Values given by Cox et
al. [89COX/WAG], supplemented by those assessed by Grenthe et al. [92GRE/FUG]. Additional
values were recalculated to be compatible with these values. In particular, the partial molar
enthalpies of solution of HCl, HBr and HI in their aqueous solutions (and that of H20) have been
recalculated from a cubic-spline fitting to the enthalpies of dilution (Φ2) given by Parker [65PAR]
as a function of the square root of the molality. The partial molar enthalpies of formation of the
solute are then given [65PAR] by the equations:
,1/2
L2 = Φ2 + m d02/dm
AfH(solute, partial) = AfH(solute, infinite dilution) + L2
and the partial molar enthalpies of formation of water by
U = -(Mj m3/2 /2000) dO>2/dm1/2
AfH(H20, partial) = AfH(H20, infinite dilution) + Li
8