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Thermochemistry of selected fission product compounds
Journal of Nuclear Materials 201 (1993) 81-91 North-Holland
Thermochemistry
of selected fission product compounds
R.G.J. Ball a, B.R. Bowsher b, E.H.P. Cordfunke
‘, S. Dickinson b and R.J.M. Konings ’
aAEA Reactor Services, Harweli Laboratory, Oxfordshire OX11 ORA, United Kingdom b AEA Reactor Services, Winfrith Technology Centre, Dorchester, Dorset DT2 SDH, United Kingdom ’ Netherlands Energy Research Foundation ECN, Petten, The Netherlands
Thermochemical data have been determined for a number of compounds of fission products and reactor materials. Critical assessments have also been made of the available thermochemical data on a number of systems. The studies have focused on the vaporization of iodides, such as indium iodide and cadmium iodide, and of ternary oxide compounds, such as caesium ruthenate, borate, molybdate and phosphate. The thermodynamic properties of condensed phases such as CdI,, Cs,CdI,, Cs,RuO,, Cs,Si,O, and Cs,ZrO, have also been measured. The data enable the speciation of fission products and their transport in the event of a severe reactor accident to be predicted with greater confidence.
1. Introduction
2. Experimental
In order to assess the consequences of a severe accident in a nuclear power plant and quantify the fission product source term, a reliable description is required of the kinetics and thermodynamics of the compounds that are likely to be formed. Such compounds arise from the interaction of the fuel and fission products both with each other and with the coolant and components of the core and primary circuit. Data for such compounds may be incorporated into mechanistic codes such as VICTORIA [l], which have been developed to calculate the thermal hydraulics and chemistry resulting from various accident scenarios. Work has been carried out on the thermodynamic characterization of a number of systems which have been identified as being of particular importance in severe accident analysis [2,3]. A wide range of experimental techniques was employed to measure the thermodynamic parameters. The systems studied were taken mainly from a list, given in table 1, compiled as a result of a specialists’ meeting held to review the current understanding of fission product chemistry during accidents in light water reactors [4]. Experimental data have so far been provided for a total of 34 compounds, with critical evaluations on a further 8 systems, as indicated in table 1. In this paper, a selection of the results from these studies is presented. A more comprehensive paper will be published at a later date.
The details of the experimental studies were described in a previous publication [2] and so only a brief summary will be given here. The reliability of the thermochemical measurements is critically dependent on the careful preparation of the samples. Most of the compounds studied are not available commercially insufficiently pure form and impurities can have a large influence on the thermochemical properties to be measured. The preparations were therefore carried out in purified gases (oxygen and water contents less than 1 ppm) and with sufficient care that no reactions occurred with the container materials. All samples were characterized for purity by X-ray diffraction and chemical analysis. A variety of calorimetric techniques was used in the study. Low-temperature heat capacity measurements were carried out at Ann Arbor Laboratory in an adiabatic calorimetric cryostat using a gold-plated calorimeter made of high conductivity, oxygen-free copper. Enthalpy increments above 298.15 K were measured in an isothermal diphenylether drop calorimeter, which is a modified version of the Bunsen-type ice calorimeter. Enthalpies of solution were measured using conventional calorimetric techniques. Vapour transport measurements were made by the transpiration technique, which is based on the principle that the saturated vapour of a sample is transported with a known volume of carrier gas and con-
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R. G.J. Ball et al. / Thermochemistv
82
Table 1 Compounds or systems recommended for study during cialists’ meeting held at JRC-Ispra, Italy in 1990 [4] A. Specific fission product compounds 1. CsOH(g). (CsOHI,(g) 2. Cs,Te(g) 3. 4. 5. 6.
CsTe(g) Cs,TeO,(c/g) Cs,TeO,(g) Csl.CsOH(g)
B. Mixed fission product-bulk 7. CsB02(g), X. InI 9. InI,( IO. In,Te(g)
Cs,B,O,(g)
In,I,(6)
Il. InZTez(g) 12. 13. 14. 15. 16. 17. 18. 19.
CdI,(g), Cd,I,(g) Cs-I&Cd-0-H(c/g) SrrB-O(c/g) Ba-B-O(c/g) %-I(g) Fe-I(g) Cr-I(g) Ni-I(g)
C. Ternary systems 20. 21. 22. 23. 24. 25. 26. 27. 28.
Cs2Ru0,(g) CszMnO,(g) Cs&rO,(g> Cs,MoO,(g) Cs-Zr-O(c/g) Cs-Si-O(c/g) Cs-Fe-O(c/g) Cs-B-O(c/g) cs-P-O(c/g)
L? Hydroxides 29. 30. 31. 32. 33. 34. 35.
Cd(OH),(g) TeO(OHIZ(g) In-O-H(g) MO-O-H(g) Ru-O-H(g) Ba-O-H(g)
Sr-O-H(g)
E. Hydrides 36. CddH(g)
37. CsH(g) 38. Ba-H(g) 39. %--H(g) 40. Sn-H(g) 41. B-H(g)
of’selected fission product compounds
densed
a spe-
in the COO~CI-part of the spectra wet-c measured on a Fourier transform spectrometer. Other vibrational spectra were recorded on a matrix isolation infrared spcctromctcr in which gaseous molecules generated at high temperatures arc trapped in inert gas matrices at cryogenic temperatures. The trapped molecules arc analysed by infrared spectroscopy and. since all rota tional movement is suppressed, the vibrational frcqucncics can be measured with great precision. apparatus.
in a collection
tube
Gas-phase
infrared
material compound.t
3. Ternary oxide compounds There are a number of ternary oxide systems that were identified at the Ispra specialists’ meeting as being of significance to severe accident analyses and requiring further quantification. In the majority of cases, these compounds are composed of fission prod uct caesium with either other fission products (e.g. molybdenum, ruthenium or zirconium), components 01 the fuel cladding (e.g. zirconium), moderator material (c.g. boron), or components of steel structural materials (e.g. manganese, silicon, phosphorus). Since cacsium is a radiobiologically significant fission product, its interaction with other materials in the reactor alfects reactor safety issues, since its compounds may retard or enhance its release. For example, caesium molybdate has been implicated in the release of fission product molybdenum from irradiated fuel [S]. However. caesium molybdate is substantially less volatile than caesium hydroxide, which is one of the forms in which caesium is normally believed to be stabilized in the primary circuit of a PWR under severe accident conditions [6]. Thus, the presence of cacsium molybdate could reduce the magnitude of the caesium release during an accident. As part of the present study, the vaporization of this compound was studied using several experimental techniques. Likewise. cacsium ruthenate combines and influences the behaviour 01 two radiobiologically important fission products [6] and has been implicated in the release of fission products during the reprocessing of nuclear fuel. Both the condensed phase and vapour phase species of this compound were studied experimentally in the present work. As mentioned above, phosphorus is a component 01 structural materials used in the primary circuit of light water reactors (stainless steel and Inconel). Although only present in trace quantities, at temperatures above
83
R G.J. Ball et al. / Thermochemistry of selected fission product compounds
1000 K phosphorus can migrate to the surface of these structural materials and react with specific fission product compounds. In particular, Elrick et al. [7] have shown that caesium hydroxide vapour reacts readily with phosphorus from the steel to form caesium phosphate (Cs,PO,). Formation of this compound could modify the release and transport of fission product caesium and so the properties of this condensed phase compound have been studied. Likewise, the properties of caesium silicate (Cs,Si,O,), caesium zirconate (Cs,ZrO,) and caesium manganate (Cs,MnO,) have been investigated. Caesium borate could be formed through the reaction of the fission product compounds caesium iodide and caesium hydroxide with the soluble neutron absorber, boric acid [6] according to the following reactions: CsI + H,BO,(g)
+ CsBO,(g)
CsOH(g) + H,BO,(g)
+ HI(g) + H,O,
4 CsBO,(g)
+ 2H,O.
Caesium borate is significantly less volatile than either caesium iodide or caesium hydroxide and so the formation of this compound could alter the transport behaviour of the released fission products considerably. The thermodynamic quantities of this molecule were determined by transpiration methods and infrared spectroscopy.
3.1. Cs,MoO,(g~ Matrix isolation infrared studies were performed on Cs,MoO&g). The observed spectra were interpreted on the basis of a distorted tetrahedral MOO, unit with bidentate coordination to two caesium atoms, as indicated by electron diffraction studies [8]. Bands in the infrared spectrum were observed at 837, 827, 369, 315, 163 and 143 cm-’ and these could be assigned to two modes, B, and E, associated with each of the predominantly MO-O stretching, O-MO-O bending and Cs-0 stretching coordinates, respectively. Together with a reported Raman frequency of 891 cm- ’ for the noninfrared active MO-O stretching mode [9], these data were used to calculate the frequencies of three of the remaining modes using the SOTONVIB program. The final remaining mode corresponds to the doubly-degenerate low-frequency torsion mode and this was estimated on the basis of previous calculations for the Cs,SO,(g) molecule [lo]. Further data required to calculate the thermal functions of the molecule are listed in table 2. The vapour pressure of Cs,MoO, was measured between 1117 and 1190 K using the transpiration technique [l]. The results are shown in fig. 1 and compared with the vapour pressures of two other volatile caesium containing species, CsBO, and Cs,RuO, measured
Table 2 Molecular
parameters
Compound
for gaseous
molecules
Vibrational
frequencies
(cm-t)
‘)
Moment
of inertia
Symmetry
group
Ternary oxides Cs 2 MOO,
891,369,
6.693x10-“’
Dz,
Cs,RuO,
315(2), 143(2), 3Ot2) -820,390,100,350,840,425,200,820(2),
6.897x
lo-“’
Dz,
CsBO,
310(2), 160(2), 30(2) 1933, 1045,632,588,233,60 _-_
1.400x
10-113
CS
177.1 b, 151,56, 236(2), 44(2) 187, 134, 69,40,35, 114,55,
2.0856X 10-r” 1.1275x10-‘“s
Iodides In1 InI, In,&
124,278,
232,49,=, Cd1 CdI, N.B.: Degeneracy of a) Underlined values b, X,O, = 0.4 cm-‘, 25050.5(6) cm-‘. c, X,W, = 0.76 cm-‘,
178.7 =’ 155.1,49.2(2), --
837, 369, 163, 828(2),
49,44,
231, 54, 15,
180,124,59 --
_
260.9
2.7405 x 10 - 37
C, Dss Dz., C, D mh
the ground electronic state was taken as unity in each case, except for CdI, where it was taken as 2. are the experimental data. B, = 3.687~ 10W2 cmm2, D, = 7.6X 10m9 cm-‘, (Y, = 1.041 X 10m4 cm-‘; excited electronic states: 24401.6(6), B, = 5.545 X 10m2 cme2;
excited
electronic
states:
23868.4(2),
28230.5(2),
29531.7(2),
41912.0(2)
cm-‘.
x4
R.G.J. Ball et al. / Thermochemists 3.0
2.0
;;i
1.0
% CL 3
0.0
-1.0
-2.0 8.0
9.0
11.0
10.0
12.0
1O4T(K) Fig. 1. Vapour
pressures
of CszRuO,,
Cs,MoO,
and CsBO,.
with the same technique [11.18]. The data can be represented by the equation given in table 3. The thermal functions derived from the infrared data were combined with the vapour pressure measurements and with thermodynamic quantities for Cs,MoO,(s) [ll] in a third-law calculation to give an enthalpy of sublimation at 298.15 K of (308.2 + 0.5) kJ mol- ‘, which is in good agreement with that reported by Johnson [12] [(309.6 + 1.1) kJmolP’], and, to a lesser extent, with that of Tangri et al. [13] [(312.4 f 0.4) kJmolP’]. Finally, this value was used to calculate the enthalpy of formation of CszMoOq(g); A,Hk(Cs,MoO,, g, 298.15 K)= -(1206.3 i 1.5) kJmol_-‘. 3.2. Cs2Ru0,(c/g) The enthalpy of formation of Cs,RuO,(s) termined by means of solution calorimetry,
was deusing 1.0
of selected fission product compound.s
moldm ’ NaOH as the solvent [14]. To derive the cnthalpy of formation of the compound, the measured cnthalpy of solution was combined with the enthalpies of solution of CsOH(s) and NaBr(s) in the same medium and with data for the enthalpies of formation of CsOH(s), NaBr(s) and NaOH(sln). The enthalpy of formation of Cs,RuO,(s) at 298.15 K was found to be: A,H;(Cs,RuO,, s. 298.15 K) = -(964.6 F 5.3) kJmol_‘. Differential scanning calorimetry was employed to study the phase transitions in this compound. A transition was found at (906.8 & 0.4) K with an enthalpy of transition of (2.78 + 0.13) kJ mol- ‘. The melting point was found to be (1211.8 & 0.3) K, with an enthalpy of fusion of (27.11 i 0.53) kJ mol- ‘_ Low-temperature heat capacities for Cs,RuO,(c) were measured from 5 to 350 K using adiabatic calorimetry. From these measurements, the heat capacity and standard entropy, at 298.15 K. were derived, their values being 156.31 and 263.07 Jmol ’ K ‘, respectively. High temperature enthalpy increments were also measured, leading to the expression given in table 4. The vapour pressure of Cs,RuO, was measured in oxygen between 1015 and 1134 K using the transpiration method [ll]. The results are shown in fig. 1 and can be represented by the equation given in table 3. Molecular parameters for the Cs,RuO,(g) molecule were cstimatcd by analogy with Cs,MoO,(g) and are given in table 2. These data were used to calculate the thermal functions for Cs2RuO&g) which were combined with the vapour pressure measurements in a third-law calculation of the enthalpy of sublimation at 298. IS K, which was found to be (249.7 + 1.5) kJ moi ’ This was then used to calculate the enthalpy of formation of CszRuO,(g) at 298.15 K: A,H&(Cs,RuO,. g. 298.15 K) = --(714.9 k 5.5) kJ mol ‘.
Table 3 Vapour pressure measurements Comoound Cs,MoO, “) &MOO, h, CsZRuO, CsBO, ” CsBO, ” “I Based on caesium
IO~(
p
/atm) = A + BAT/K)
A
B
- 14470.5+ 584.7 - 14229.3? 653.6 - 8307.7 + 139.4 -14159 i375 -12098 k689
12.038 * 0.507 11.850 f 0.567 X.292* 0.128 15.537 * 0.407 13.458f0.665
analyses. I’) Based on molybdenum analyses.
” Over solid. d’ Over liquid.
T range (K) 1117 to 1117 to 1015 to 867 to 997 to
1190 1190 1168 982 1087
A,,,,,H”(298.15 K) (Jmol-‘)
Ref.
308.4 f 0.5 308.8 f 0.5 249.7 i 1.5 270.8 rf-0.7 269.0 &0.X
[ItI [LII [Lll
iI81 [I81
-
R.G.J. Ball et al. / Thermochemistry of selected fission product
3.3. Cs, MnO,k)
85
compounds
of CsOH(c), the enthalpy of formation of Cs3P04 at 298.15 K was found to be: A,Hk(Cs,PO,, S, 298.15 K) = -(1910.9 & 1.5) kJmol-‘. Differential scanning calorimetry was used to study the phase transitions in this compound. A reversible phase transition was found at (868.6 k 0.5) K, with an enthalpy of transition of (4.75 + 0.15) kJ mol- ‘.
tion
Low-temperature heat capacity measurements (5 to 350 K) were made on Cs,MnO,(c) by adiabatic calorimetry [15]. The heat capacity and standard entropy, at 298.15 K, were 155.0 and 240.6 Jmol-’ K-l, respectively. High-temperature enthalpy increments were also measured, leading to the expression in table 4. Cs,MnO, is isostructural with Cs,RuO, and has a phase transition in the solid state. Differential scanning calorimetric measurements showed this transition to be at (1052.0 + 5.0) K, with an enthalpy of transition of (0.59 + 0.08) kJ mol-‘. The melting point was determined as (1176.7 +_2.0) K. However, due to a reaction with the container materials, the enthalpy of fusion could not be measured. By comparison with the values for Cs,CrO,, Cs,MoO,, Cs,RuO, the enthalpy of fusion was estimated to be (21.0 k 0.5) kJmol_‘. The enthalpy of formation of Cs,MnO, was determined by solution calorimetry, using an aqueous solution of 4.032 moldmm3 H,SO, with 0.106 moldm-3 FeSO, as the solvent. The value at 298.15 K is: AfHk(Cs,MnO,, s, 298.15 K) = -(1179.5 + 3.0) kJmol_‘.
3.5. Cs,Si,O, The enthalpy of solution of Cs,Si,O, in HF(aq) was measured at 298.15 K [16]. By combining this value with the enthalpies of solution of a (SiO, + CsF) mixture in the same solvent, the enthalpy of formation was calculated to be: ArH&(Cs,Si,O,, s, 298.15 K) = -(4297.6 + 5.4) kJ mol-‘. The enthalpy increment of this compound was measured from 475 to 825 K, and the results are shown in fig. 2. By fitting the results to a polynomial with C&298.15 K) = 239.0 J K- ’ mol- ’ as a boundary condition, the expression given in table 4 was obtained. 3.6. Cs, ZrO,(c) The enthalpy increments of Cs,Zr03 from 451 to 641 K were measured, as shown in fig. 2. No measurements were made above 641 K due to reaction with the container material. Fitting of the results with C&298.15 K) = 126.0 JK-’ mole1 as a boundary condition gave the expression in table 4. The enthalpy of formation at 298.15 K of this compound, as reported by Cordfunke
3.4. Cs,POJc) The enthalpy of solution of Cs,PO, was measured in an aqueous solution of 0.034 moldmm3 H,PO,. Combined with the enthalpy of solution of CsOH measured in the same medium and the enthalpy of forma-
Table 4 Calorimetric
data
Compound
Cs,RuO,(s) Cs,MnO,(s) Cs,Si,O,(s) Cs,ZrO,(s) CdI &I CdI,W Cs,CdI,(s) Cs&dI,(s) Cs,CdI,(I) a) Enthalpy b, Enthalpy ‘) Enthalpy
A,H” (298.15 K) (kJ mol-‘)
- 964.6 + - 1179.5 f - 4297.6 + -1584.8+1.9 - 205.3 + _ a) b, ‘) increments increments increments
S (298.15 K) (Jmol-‘Km’)
5.3 3.0 5.4 0.9
- 920.3 + 1.4 _
for temperatures for temperatures for temperatures
263.07 240.60 313.00 200.00 157.61 _404.00 _
H(T)-
H(298.15
K)= ACT/K)+
B(T/K)’
+ C/CT/K)+
D
(JmolF’K-‘1 A
B x lo3
129.5580 99.8760 367.1725 167.3315 69.4374 111.1932 404.2505 231.0000 250.0000
44.8631 88.3800 0.50538 - 2.6252 13.5714 _ - 126.2530 _
up to 400 K. between 400 and 704 K. between 704 and 1000 K.
_
c x10-s
- 1.858 - 114.205 35.954 _ 120.76 _
D - 42616.00 - 37011.00 - 147822.00 - 61715.50 - 21909.20 - 23309.70 - 149807.30 - 67367.61 - 44043.61
X6
R.G.J. Ball et al. / Thermochemistry
300
LOO
500
600
700
800
TIK
Fig. 2. The reduced
enthalpy increment of solid Cs,Si,O,j and Cs,ZrO, (0).
(o)
et al. 1171, is: A,H$Cs,ZrO,,
s, 298.15 K) = -(1584.8 f 1.9) kJmol_‘, and an estimated value for the standard entropy at 298.15 K is 200.0 JK-’ mol I.
3.7. CsBO,(g)
The gas-phase vibrational spectrum of CsBO, was studied from 25 to 3000 cm-’ at a resolution of 0.5 cm -‘. Four major absorptions were observed in the range from 3000 to 375 cm-’ at 1933, 1045, 632 and 588 cm- ‘. Between 350 and 25 cm- ‘, only one absorption was found, at 232.8 cm-‘. The intensities of the peaks increased with increasing temperature, implying that they can be attributed to C&O, species. The bandwidth also increased with increasing temperature and at 1390 K, it was difficult to discriminate between the 632 and 588 cm- ’ peaks. Minor absorptions were observed at 1190 and 1385 cm-‘, but the intensities of these peaks increased with time rather than with temperature. It was concluded that these peaks arose from condensation of the vapour species in the cell atmosphere and on cell windows. Solid CsBO, exhibits its strongest absorptions at 1183 and 1379 cm-’ at room temperature. The peaks in the gas-phase infrared spectrum could be assigned on the basis of a bent molecule with a linear O-B = 0 group. Matrix isolation infrared spectra were also measured for CsBO,. The mid-infrared (2500 to 400 cm-‘) spectrum of the vapour was dominated by doublets at 1956/2026 and 575/594 cm-‘. A third, weaker doublet was also observed at 1073/1080 cm-‘. The intensity ratio of the two components was 4 in all three doublets and this is indicative of the presence of natural boron (20% ‘“B, 80% “B). The peaks in the matrix
of selected fission product compounds
infrared spectrum correspond to those in the gas-phase spectrum, apart from the absence of an analoguc to the gas-phase frequency at 632 cm ‘. However, a shoulder was observed on the 574 cm ’ band at 579 cm- ‘. The low frequency region of the spectrum (400 to 30 cm- ’ ) contained bands at 336 and 300 cm ‘. A very weak band at 205 cm-’ was also observed which was assigned to the Cs-0 stretching mode of CsBO?. The gas-phase frequencies were used to calculate the thermal functions for CsBO, over the temperature range 298 to 3000 K. The molecular parameters are given in table 2. The equilibrium vapour pressures over both solid and liquid CsBO, were measured by means of the transpiration method [18]. If it is assumed that only gaseous monomeric species are present. as indicated by mass spectrometric results [19], then the vapour pressure over solid and liquid CsBO, can be represented by the equations given in table 3. A third law calculation based on these vapour pressure measurements gave the cnthalpies of sublimation also given in table 3. The slight difference in the values derived for the solid and liquid data may be due to the fact that the thermodynamic parameters arc less accurately known for liq-. uid CsBO, than for the solid.
4. Iodides The interest in the iodides of indium and cadmium arise from the potential reactions between fission product iodine with control rod material [7]. In this work, the vaporization behaviour of indium and cadmium iodidcs was studied by mass spectrometry and matrix isolation infrared spectroscopy. In addition, critical assessmcnts of thermodynamic properties of the vapour phase indium iodides were carried out. The formation of ternary caesium-cadmium-iodine compounds, such as Cs?CdI,, in the primary circuit has been postulated to occur as a result of the reaction of caesium iodide with cadmium or cadmium iodide aerosol, according to 2CsI(g)
+ CdI,(s,
I) --j Cs,CdI,(s,
I).
Such reactions could result in changes in the volatilities of fission product iodine and caesium. Evidence for reactions of this type can be found in experimental studies of the interaction of caesium iodide vapour with aerosols generated from control rod alloy samples [20]. Hence, in this work, the CsI-CdI, phase diagram was studied using differential thermal analysis to identi@ and characterize the possible condensed phase compounds.
87
R.G.J. Ball et al. / Thermochemistry of selected fission product compounds
and eventually to In1 and I, occurs. The observed infrared frequencies for InI, InI, and In,I, were combined with other molecular constants in the literature (see table 2) to calculate the thermal functions for the molecules. For InI( S”(298.15 K) was calculated to be 267.34 J K- ’ mol-’ and C&298.15 K), 37.11 JKP1mol-‘. For InI,( the values were: 400.34 J KP ’ mol - ’ and 80.99 J K- ’ molt ‘, respectively, and for In,I,(g), 637.00 J K-’ mol-’ and 178.76 J K- ’ mol- ‘, respectively. A critical assessment of the enthalpies of formation of the vapour phase indium iodides was carried out. There are five recent determinations of the vapour pressure of InI, one for the solid from 470 to 557 K [24], and four for the liquid, from 640 to 1010 K [25], from 640 to 773 K [26], from 638 to 1015 K [27] and from 646 to 958 K [28]. As shown in fig. 4, there is excellent agreement between these studies, except for the less precise values of Federov et al. [26], and the extrapolated lines for the solid and liquid intersect within the known range of the melting point 624-638 K. All the studies involving In1 stress the difficulty of preparing InI free from higher iodides and the higher vapour pressures measured by Federov et al. [26] probably result from such impurities. This is presumably also true for the early study by Robert [29] which gives pressures higher than those in fig. 4 by about a factor of four. The analysis of the vapour pressure data by the third law method is summarized in table 5. The selected value for the enthalpy of sublimation of In1 is InI,
b
Wavenumber
i cm-‘1
Fig. 3. Argon matrix infrared spectra from indium tri-iodide vaporization at 390 K. (a) No superheating, (b) vapour superheated to 770 K, (c) vapour superheated to 970 K.
4.1. In-l
Matrix isolation infrared studies of the vapour at 400 K gave a more complicated spectrum than that expected for InI, molecules, see fig. 3. Four bands were observed at 231, 180, 160 and 124 cm-‘. These could be assigned to the infrared-active In-I stretching modes of the dimeric molecule In,I, and are close to those reported for solid phase indium(II1) iodide [21,22], which consists of discrete In,I, molecules. On superheating to 770 K, the intensities of the four dimer bands decreased and the spectrum was dominated by a single band at 236 cm-l (see fig. 3). This was assigned as the asymmetric In-I stretching frequency of a planar InI, molecule. At 970 K, this band also decreased in intensity and a new, sharp band at 167.7 cm-’ became the dominant feature. This latter frequency was assigned to InI, though it is shifted somewhat from the gas-phase value for this molecule (177 cm-’ [23]). Such a shift is not uncommon for matrix-isolated molecules with a significant dipole moment, as expected for InI. Thus, the vaporization of indium(II1) iodide at low temperatures yields In,&, but as the temperature of the vapour increases, dissociation to
1
-5 -6 -
= Barrow et al. [24] 0 Brumleve et al. c281 + Grinberg et al. c251 x Chusova et al. [271 0 Federov et al. C261
-7 - -Assessed -8. 0.9
I 1.1
data I 1. 3
I 1.5
I 1.7
I 1.9
IO3 I T IK-‘1
Fig. 4. Vapour pressure of InI.
I 2-l
I 23
xx
R. G.J. t3dI
et al. /
of’selected fi.s.siorr product
Thennochetni.stry
c~m1po~m1.s
Table 5 Vapour pressure studies for InI(g) -__ References
T(mean) (K)
Smith and Barrow [%I Grinberg et al. [25] Chusova et al. [27] Brumleve et al. [2X]
525 825 x75 X02
log ,,,p /atm .4/T+R
=
il
H
~ 0565.6 5290.0
7.230 5.210
(129.0-t 1.5) kJmol ‘. This lcads to: L,N;(lnl. g. 298.15 K) = 26.5 kJ mol ‘. This is somewhat more positivc than that derived from the dissociation cncrgy at 0 K of 3.43 CV given by Huber and Herzbcrg [30]. Correction to 298.15 K gives 333.0 kJ mol ’ for the dissociation enthalpy to In and I gases, which with enthalpies of formation of 240.4 [3 1] and 106.8 kJ mol ’ [32] respectively, gives an enthalpy of formation for In1 (g) of 14.1 kJmol I. Presumably In(g) or I(g) is in an excited state in this dissociation. The cnthalpies of formation of InI, and In,I,(g) arc not easy to define since. as shown earlier, although InI, is quite volatile, both monomer and dimcr occur in the gas phase, even at low tcmperaturcs, while above 650 K, dissociation to InI and perhaps also divalent iodides InI, and/or InlI,(g) occurs. Howcvcr, the cnthalpies of formation for thcsc species wcrc derived as follows. The studies of the reaction InI,
--f InI
+ I,(g)
by Titov and Chusova [33]. Zaidova et al. 1341 and Grinberg et al. [35] wcrc analyscd to provide A, Hi,(InI,, g). This was then combined with data for the dimerization reaction 2Inl,(g)
+ In,I,,(g)
to obtain AfH,“,(In,l,,. g). The values obtained for the enthalpics of formation were: AfHi,(InI;. g, 29X.1 K) = -(104.0 F 4.0) kJmol_ ’ and A,Hz,(Inz16, g. 298.15 K) = -(326.0 i 12) kJmol ‘. In the final optimization, thcsc cnthalpics of formation were used and the standard entropy of InI, adjusted to give rcasonable agreement with the vaporization information from Smith and Barrow [36]. Fcderov et al. [37] and Girichcva ct al. [3X]. With a value for S(In1,. c, 29X.15 K) of 222.0 + 10 J K ’ mol ‘, good agreement was obtained with ai the data cxccpt for that of Fcderov et al. [37]. which has internal inconsistencies in the published data: even there, agreement was probably within cxpcrimcntal error. The correct boiling point of 773 K was obtained by selecting the reasonable value of IX.3
AS(exp)
AS(calc)
13-L-I
137.5 137.5
97.1
-. A,,,,,11(2YX.l5 K) third Ia\\
179.7 t I.?
IXJ.0t- 0.r;
kJ mol ’ for A,,,,H(4XO IO, in tolcrahlc agrccmcnt with the preliminary value of 14 kJ mol ’ mcasurcd bb Ncwland 1391. ‘!.‘?. (‘d-i Previous studies of cadmium iodide by mass spcctromctry have shown that the predominant spccics i\ monomeric Cdl, [40]. However, studies have also indicated the prescncc of small amounts of polymeric (probably dimcr) species [41]. The matrix isolation infrared spectrum of cadmium iodide vapour was dominated by a peak at 265.7 (Ar matrix) or 260.9 cm ’ (N, matrix) with a much weaker peak at 49.7 (Ar matrix) OI49.2 cm ’ (N, matrix). Additional bands at 217.7 and 153.6 cm ’ were assigned to polymeric species formed in the matrix since the intcnsitica of the features rcla-tive to the main peak varied under different deposition conditions. The measured frequencies were combined with a previously-reported Raman frequency for the infrared-inactive totally symmetric stretching mode (155.1 cm ’ [42]) and a value for the Cd-1 bond length of 0.255 nm [43] in order to calculate the thermal functions for the molcculc (see table 2). In the condensed phase, the cnthalpy incrcmcnts ot solid as well as liquid CdI, wcrc measured from 477 to X59 K. The data were fitted to polynomials, one for the solid phase (29X.1.5 to 654 K) and one for the liquid phase as shown in table 4. For the solid phase. the boundary condition, C&298.15 K) = 77.53 J K- ’ mol ’ was used during the fitting procedure. The cnthalpy ot solution at 29X.15 K of CdI.(s) in H,SO, was mcasured. By combining the resu?ts with the cnthalpies ol solution of CdO, KI and K,SO, in the same medium. the cnthalpy of formation of the compound was found to bc S,H;(CdI,, s. 29X.15 K) = -(205.3 + 0.0) kJ mol ‘. Differential scanning calorimetric mcasuremcnts were cmploycd to dctcrmine the melting point of Cdl,. This was found to be at (654 & 2) K. From the cnthalpy
R.G.J. Ball et al. / Thermochemistry of selected fission product compounds
The heat capacity, enthalpy change for the solid state transition and enthalpy of fusion for Cs,CdI, were determined by means of differential scanning calorimetry. The heat capacity data were fitted to polynomials in temperature, as given in table 4. The enthalpy change for the solid state transition was 3150 Jmol-‘, while the enthalpy of fusion was 36.7 kJmol_‘, with an uncertainty of 1% in the data. The enthalpy of formation of Cs,CdI,(s) was determined by solution calorimetry using H,SO,(aq) as the solvent. The value obtained was A,&(Cd,CdI,, s, 298.15 K) = -(920.3 f 1.4) kJmol_‘. The only previous value for the enthalpy of formation of this compound, - (916.6 k 3.5) kJ mol-’ was reported by Auffredic and Touchard [45], who measured the enthalpy of solution of Cs,CdI,(s) in water. Recalculating their thermochemical cycle with the same auxiliary data for CsIW and CdI,(s) used in this study gives a value for the enthalpy of formation of -(917.7 + 1.5) kJmol_’ which is in reasonable agreement with the present result.
increment equations for solid and liquid CdI,, the enthalpy of fusion is calculated to be 20.10 kJmoll’. 4.3. Cs-Cd-I The CsI-CdI, phase diagram was studied using differential thermal analysis. As shown in fig. 5, the only compound observed in these studies was Cs,CdI, with a melting point of (702 k 1) K. Two phases (a and p) of this compound were observed and positively identified by hot cell X-ray diffraction. The transition between the two phases was found to be reversible. However, unlike the (Yto l3 transition, which was fast, the p to cx transition required in excess of 14 days for completion, in agreement with earlier observations by Touchard et al. [44]. The temperature of transition depended on the composition: the transition occurred at 430 K in excess CsI, compared with 400 K for the pure compound, implying that the large Cs+ ions were more readily accommodated in the a-Cs$dI, lattice.
3
600 -
0
20
89
40
Fig. 5. CsI-CdI,
60
phase diagram.
80
00
R.G.J. Bali et al. / Thermochemistry
5. Conclusions Experimental studies and critical assessments have been undertaken to obtain thermochemical data for selected compounds of fission products and reactor materials. The choice of compounds was based on the recommendations of a specialists’ meeting held at JRC-Ispra, Italy in 1990 [4]. In this report, a selection of results from the study were presented. The work carried out represents a significant improvement in the thermodynamic database for reactor materials and fission products and will permit a more comprehensive assessment of the fission product source term to be made. This will enable the consequences of a severe accident in a nuclear plant to be predicted with greater confidence on a mechanistic basis.
Acknowledgements The authors wish to thank A.L. Nichols, M.S. Newland, J.S. Ogden, P.E. Potter, I.R. Beattie, E.F. Westrum, Jr., M.H. Rand, J. Drowart and C.A. Alexander for helpful discussions associated with this work, M.S. Newland, J.S. Ogden, N.E. Freemantle, V. Smit-Groen, W. Ouweltjes, R. v.d. Laan and A.S. Booij for assistance with the experimental work, and S.J. Wood and B.A. Bellamy for analytical chemistry support. The Dutch work was funded in part by the Commission of the European Communities, Joint Research Centre, Ispra (Research Contract No. 38768912 EL ISP NL). The UK studies were funded by the Commission of the European Communities, Joint Rcsearch Centrc, Ispra (Research Contract No. 3871-89. 12 EL ISP GB), the UK Health and Safety Executive (PWR task SAA 3.1), the General Nuclear Safety Programme (task FPB5), and the AEA Corporate Research Programme.
References [II T.J. Heames, D.A. Williams. N.E. Bixler, A.J. Grimley. C.J. Wheatley, N.A. Johns and N.M. Chown, VICTORIA: A Mechanistic Model of Radionuclide Behaviour in the Reactor Coolant System Under Severe Accident Conditions, Sandia National Laboratory Report for US Nuclear Regulatory Commission, NUREG/CR-554s (1990). [?I R.G.J. Ball, B.R. Bowsher, S. Dickinson, E.H.P. Cordfunke, R.J.M. Konings and M.H. Rand, Thermochemical Data Acquisition, Commission of the European Communities Report, EUR 14004 EN (1991).
of selected fissiotz product compounds 131R.G.J. Ball, S. Dickinson,
E.H.P. Cordfunke and R.J.M. Konings, Thermochemical Data Acquisition, part II. Netherlands Energy Research Foundation ECN, Report No. ECN-C-92-033 (1992); to he published as Commission of the European Communities EUR-report. in Severe I41 AL. Nichols, ed., Fission Product Chemistry Nuclear Reactor Accidents, Specialists’ Meeting at JRCIspra, IS-17 January 1990, UKAEA Report, AEA-TRS5024 (1990) and Commission of the European Communities Report, EUR 12989 EN (1990). [51 J.K. Fink, M.F. Roche. C.A. Seiis. D.V. Steidl, and C‘.t. Johnson, Proc. ACS Symp. on Chemical Phenomena Associated with Radioactivity Releases During Severe Nuclear Plant Accidents, NUREG/CP-0078 (1986). [61 B.R. Bowsher, Prog. Nucl. Energy 20 (1987) 199. [71 R.M. Elrick, R.A. Sallach, A.L. Ouellette and S.C. Douglas, USNRC Report NUREG/CR-3197, vol 1 (lYX4). [81 V.V. Ugarov. Y.S. Ezhov and N.G. Rambidi, J. Mol. Structure 25 (1975) 2140. L. Bencivenni and K.A. Gingerich, J. [91 H.M. Nagarantha, Chem. Phys. 81 (1984) 591. [lOI A.A. Belyaeva, M.I. Dvorkin and L.D. Shecherba. Opt. Spectrosc. 38 (1975) 170. [III EJ1.P. Cordfunke, R.J.M. Konings and S.R.M. Meysscn. J. Chem. Thermodyn. 24 (1992) 725. [I21 I. Johnson, J. Phys. Chem. 79 (1975) 722. 1131 R.P. Tangri, V. Venugopal, D.K. Bose and M. Sundaresari,, J. Nucl. Mater. 167 (1989) 127. R.J.M. Konings, W. Ouwekjes and P. 114J E.H.P. Cordfunke, van Vlaanderen, J. Chem. Thermodyn. 22 (1990) 285. and E.F. Westrum, Jr.. to he pub[lSl E.H.P. Cordfunke lished. Llhl E.H.P. Cordfunke and W. Ouweltjes. to be published. [I71 E.H.P. Cordfunke. W. Ouweltjes and P. van Vlaanderen, J. Chem. Thermodyn. 19 (1987) II 17. [I81 E.H.P. Cordfunke, R.J.M. Konings and S.R.M. Meyssen. J. Chcm. Thermodyn. 23 (lY91) 297. A.V. Gusarov. A.V. Makarov and 0.7’. [191 L.N. Gorokhov. Nikitin, Teplofiz. Vys. Temp. 9 (1971) 1173. [201 A.M. Beard, C.G. Benson and B.R. Bowshcr, UKAEA Report AEEW-R 2470 (I 988) [211 D.M. Adams and R.G. Churchill, J. Chem. Sot, (A) (I(3683 2141. 1221 I.R. Beattie. T. Gilson and G.A. Ozin. J. Chem. Sot. iA) (1968) 813. [231 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds (Wiley. New York. 197X). I241 R.F. Barrow, A.C. Pugh and F.J. Smith, Trans. Farad. sot. 51 (195.5) 1657. [251 Y.K. Grinberg, V.A. Boryakova, V.F. Shevel’kov and Z.S. Medvedeva, Izv. Akad. Nauk SSSR Neorg. Mater. X (lY72) 07. [261 P.1. Federov, N.S. Malova and Yu.N. Denisov. Russ. J. Inorg. Chem. 21 (1976) 640. [271 T.P. Chusova. N.I. Matskuvich. Yu.G. Stenin and (;.A. Kokovin. Jzv. Sib. Otd. Akad. Nauk. SSSR. Ser. Khim. Nauk. 5 (1979) 62.
R.G.J. Ball et al. / Thermochemistry of selected fusion product compounds [28] T.R. Brumleve, S.A. Mucklejohn and N.W. O’Brien, J. Chem. Thermodyn. 21 (1989) 1193. [29] G. Robert, Helv. Phys. Acta 9 (19361 405. [30] K.P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, vol. IV, Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 19791. [31] V.P. Glushko et al., Thermodynamic Properties of Individual Substances, vol. II (Akademy Nauka, Moscow, 19811. [32] J.D. Cox, D.D. Wagman and V.A. Medvedev, CODATA Key Values for Thermodynamics (Hemisphere, New York, 1989). [33] V.A. Titov and T.P. Chusova, Isv. Sib. Otd. Akad. Nauk. SSSR, Ser. Khim. Nauk. 1 (1987) 75. [34] G.A. Zaidova, S.M. Gadzhiev and A.A. Kuliev, Russ. J. Inorg. Chem. 48 (1974) 617. [35] Y.K. Grinberg, V.A. Boryakova and V.F. Sheve’kov, Isv. Akad. Nauk. SSSR Neorg. Mater. 12 (1964) 551. [36] F.J. Smith and R.F. Barrow, Trans. Faraday Sot. 54 (1958) 827.
91
[37] P.I. Federov, A.G. Dudareva and N.F. Drobot, Russ. J. Inorg. Chem. 25 (1963) 1739. [38] N.I. Giricheva, V.M. Petrov, B.V. Girichev, V.A. Titov, T.P. Chusova and G.A. Kokovin, Isv. Sib. Otd. Akad. Nauk. SSSR, Ser. Khim. Nauk. 3 (1986) 23. [39] MS. Newland., AEA Technology, Winfrith, private communication (1989). [40] S. Dickinson, UKAEA Report AEEW-R 2227 (1987). [41] L. Topor and I. Moldoveanu, Rev. Rom. Chim. 19 (1974) 985. [42] A. Strull, A. Givan and A. Loewenschuss, J. Mol. Spectrosc. 62 (1976) 283. [43] P.A. Akishin and V.P. Spiridinov, Kristallographia 2 (1957) 475. [44] V. Touchard, M. Louer and D. Louer, Powder Diffr. 1 (1986) 35. 1451 J.P. Auffredic and V. Touchard, Thermochim. Acta 162 (1990) 463.
Thermochemistry
of selected fission product compounds
R.G.J. Ball a, B.R. Bowsher b, E.H.P. Cordfunke
‘, S. Dickinson b and R.J.M. Konings ’
aAEA Reactor Services, Harweli Laboratory, Oxfordshire OX11 ORA, United Kingdom b AEA Reactor Services, Winfrith Technology Centre, Dorchester, Dorset DT2 SDH, United Kingdom ’ Netherlands Energy Research Foundation ECN, Petten, The Netherlands
Thermochemical data have been determined for a number of compounds of fission products and reactor materials. Critical assessments have also been made of the available thermochemical data on a number of systems. The studies have focused on the vaporization of iodides, such as indium iodide and cadmium iodide, and of ternary oxide compounds, such as caesium ruthenate, borate, molybdate and phosphate. The thermodynamic properties of condensed phases such as CdI,, Cs,CdI,, Cs,RuO,, Cs,Si,O, and Cs,ZrO, have also been measured. The data enable the speciation of fission products and their transport in the event of a severe reactor accident to be predicted with greater confidence.
1. Introduction
2. Experimental
In order to assess the consequences of a severe accident in a nuclear power plant and quantify the fission product source term, a reliable description is required of the kinetics and thermodynamics of the compounds that are likely to be formed. Such compounds arise from the interaction of the fuel and fission products both with each other and with the coolant and components of the core and primary circuit. Data for such compounds may be incorporated into mechanistic codes such as VICTORIA [l], which have been developed to calculate the thermal hydraulics and chemistry resulting from various accident scenarios. Work has been carried out on the thermodynamic characterization of a number of systems which have been identified as being of particular importance in severe accident analysis [2,3]. A wide range of experimental techniques was employed to measure the thermodynamic parameters. The systems studied were taken mainly from a list, given in table 1, compiled as a result of a specialists’ meeting held to review the current understanding of fission product chemistry during accidents in light water reactors [4]. Experimental data have so far been provided for a total of 34 compounds, with critical evaluations on a further 8 systems, as indicated in table 1. In this paper, a selection of the results from these studies is presented. A more comprehensive paper will be published at a later date.
The details of the experimental studies were described in a previous publication [2] and so only a brief summary will be given here. The reliability of the thermochemical measurements is critically dependent on the careful preparation of the samples. Most of the compounds studied are not available commercially insufficiently pure form and impurities can have a large influence on the thermochemical properties to be measured. The preparations were therefore carried out in purified gases (oxygen and water contents less than 1 ppm) and with sufficient care that no reactions occurred with the container materials. All samples were characterized for purity by X-ray diffraction and chemical analysis. A variety of calorimetric techniques was used in the study. Low-temperature heat capacity measurements were carried out at Ann Arbor Laboratory in an adiabatic calorimetric cryostat using a gold-plated calorimeter made of high conductivity, oxygen-free copper. Enthalpy increments above 298.15 K were measured in an isothermal diphenylether drop calorimeter, which is a modified version of the Bunsen-type ice calorimeter. Enthalpies of solution were measured using conventional calorimetric techniques. Vapour transport measurements were made by the transpiration technique, which is based on the principle that the saturated vapour of a sample is transported with a known volume of carrier gas and con-
Elsevier Science Publishers B.V.
details
R. G.J. Ball et al. / Thermochemistv
82
Table 1 Compounds or systems recommended for study during cialists’ meeting held at JRC-Ispra, Italy in 1990 [4] A. Specific fission product compounds 1. CsOH(g). (CsOHI,(g) 2. Cs,Te(g) 3. 4. 5. 6.
CsTe(g) Cs,TeO,(c/g) Cs,TeO,(g) Csl.CsOH(g)
B. Mixed fission product-bulk 7. CsB02(g), X. InI 9. InI,( IO. In,Te(g)
Cs,B,O,(g)
In,I,(6)
Il. InZTez(g) 12. 13. 14. 15. 16. 17. 18. 19.
CdI,(g), Cd,I,(g) Cs-I&Cd-0-H(c/g) SrrB-O(c/g) Ba-B-O(c/g) %-I(g) Fe-I(g) Cr-I(g) Ni-I(g)
C. Ternary systems 20. 21. 22. 23. 24. 25. 26. 27. 28.
Cs2Ru0,(g) CszMnO,(g) Cs&rO,(g> Cs,MoO,(g) Cs-Zr-O(c/g) Cs-Si-O(c/g) Cs-Fe-O(c/g) Cs-B-O(c/g) cs-P-O(c/g)
L? Hydroxides 29. 30. 31. 32. 33. 34. 35.
Cd(OH),(g) TeO(OHIZ(g) In-O-H(g) MO-O-H(g) Ru-O-H(g) Ba-O-H(g)
Sr-O-H(g)
E. Hydrides 36. CddH(g)
37. CsH(g) 38. Ba-H(g) 39. %--H(g) 40. Sn-H(g) 41. B-H(g)
of’selected fission product compounds
densed
a spe-
in the COO~CI-part of the spectra wet-c measured on a Fourier transform spectrometer. Other vibrational spectra were recorded on a matrix isolation infrared spcctromctcr in which gaseous molecules generated at high temperatures arc trapped in inert gas matrices at cryogenic temperatures. The trapped molecules arc analysed by infrared spectroscopy and. since all rota tional movement is suppressed, the vibrational frcqucncics can be measured with great precision. apparatus.
in a collection
tube
Gas-phase
infrared
material compound.t
3. Ternary oxide compounds There are a number of ternary oxide systems that were identified at the Ispra specialists’ meeting as being of significance to severe accident analyses and requiring further quantification. In the majority of cases, these compounds are composed of fission prod uct caesium with either other fission products (e.g. molybdenum, ruthenium or zirconium), components 01 the fuel cladding (e.g. zirconium), moderator material (c.g. boron), or components of steel structural materials (e.g. manganese, silicon, phosphorus). Since cacsium is a radiobiologically significant fission product, its interaction with other materials in the reactor alfects reactor safety issues, since its compounds may retard or enhance its release. For example, caesium molybdate has been implicated in the release of fission product molybdenum from irradiated fuel [S]. However. caesium molybdate is substantially less volatile than caesium hydroxide, which is one of the forms in which caesium is normally believed to be stabilized in the primary circuit of a PWR under severe accident conditions [6]. Thus, the presence of cacsium molybdate could reduce the magnitude of the caesium release during an accident. As part of the present study, the vaporization of this compound was studied using several experimental techniques. Likewise. cacsium ruthenate combines and influences the behaviour 01 two radiobiologically important fission products [6] and has been implicated in the release of fission products during the reprocessing of nuclear fuel. Both the condensed phase and vapour phase species of this compound were studied experimentally in the present work. As mentioned above, phosphorus is a component 01 structural materials used in the primary circuit of light water reactors (stainless steel and Inconel). Although only present in trace quantities, at temperatures above
83
R G.J. Ball et al. / Thermochemistry of selected fission product compounds
1000 K phosphorus can migrate to the surface of these structural materials and react with specific fission product compounds. In particular, Elrick et al. [7] have shown that caesium hydroxide vapour reacts readily with phosphorus from the steel to form caesium phosphate (Cs,PO,). Formation of this compound could modify the release and transport of fission product caesium and so the properties of this condensed phase compound have been studied. Likewise, the properties of caesium silicate (Cs,Si,O,), caesium zirconate (Cs,ZrO,) and caesium manganate (Cs,MnO,) have been investigated. Caesium borate could be formed through the reaction of the fission product compounds caesium iodide and caesium hydroxide with the soluble neutron absorber, boric acid [6] according to the following reactions: CsI + H,BO,(g)
+ CsBO,(g)
CsOH(g) + H,BO,(g)
+ HI(g) + H,O,
4 CsBO,(g)
+ 2H,O.
Caesium borate is significantly less volatile than either caesium iodide or caesium hydroxide and so the formation of this compound could alter the transport behaviour of the released fission products considerably. The thermodynamic quantities of this molecule were determined by transpiration methods and infrared spectroscopy.
3.1. Cs,MoO,(g~ Matrix isolation infrared studies were performed on Cs,MoO&g). The observed spectra were interpreted on the basis of a distorted tetrahedral MOO, unit with bidentate coordination to two caesium atoms, as indicated by electron diffraction studies [8]. Bands in the infrared spectrum were observed at 837, 827, 369, 315, 163 and 143 cm-’ and these could be assigned to two modes, B, and E, associated with each of the predominantly MO-O stretching, O-MO-O bending and Cs-0 stretching coordinates, respectively. Together with a reported Raman frequency of 891 cm- ’ for the noninfrared active MO-O stretching mode [9], these data were used to calculate the frequencies of three of the remaining modes using the SOTONVIB program. The final remaining mode corresponds to the doubly-degenerate low-frequency torsion mode and this was estimated on the basis of previous calculations for the Cs,SO,(g) molecule [lo]. Further data required to calculate the thermal functions of the molecule are listed in table 2. The vapour pressure of Cs,MoO, was measured between 1117 and 1190 K using the transpiration technique [l]. The results are shown in fig. 1 and compared with the vapour pressures of two other volatile caesium containing species, CsBO, and Cs,RuO, measured
Table 2 Molecular
parameters
Compound
for gaseous
molecules
Vibrational
frequencies
(cm-t)
‘)
Moment
of inertia
Symmetry
group
Ternary oxides Cs 2 MOO,
891,369,
6.693x10-“’
Dz,
Cs,RuO,
315(2), 143(2), 3Ot2) -820,390,100,350,840,425,200,820(2),
6.897x
lo-“’
Dz,
CsBO,
310(2), 160(2), 30(2) 1933, 1045,632,588,233,60 _-_
1.400x
10-113
CS
177.1 b, 151,56, 236(2), 44(2) 187, 134, 69,40,35, 114,55,
2.0856X 10-r” 1.1275x10-‘“s
Iodides In1 InI, In,&
124,278,
232,49,=, Cd1 CdI, N.B.: Degeneracy of a) Underlined values b, X,O, = 0.4 cm-‘, 25050.5(6) cm-‘. c, X,W, = 0.76 cm-‘,
178.7 =’ 155.1,49.2(2), --
837, 369, 163, 828(2),
49,44,
231, 54, 15,
180,124,59 --
_
260.9
2.7405 x 10 - 37
C, Dss Dz., C, D mh
the ground electronic state was taken as unity in each case, except for CdI, where it was taken as 2. are the experimental data. B, = 3.687~ 10W2 cmm2, D, = 7.6X 10m9 cm-‘, (Y, = 1.041 X 10m4 cm-‘; excited electronic states: 24401.6(6), B, = 5.545 X 10m2 cme2;
excited
electronic
states:
23868.4(2),
28230.5(2),
29531.7(2),
41912.0(2)
cm-‘.
x4
R.G.J. Ball et al. / Thermochemists 3.0
2.0
;;i
1.0
% CL 3
0.0
-1.0
-2.0 8.0
9.0
11.0
10.0
12.0
1O4T(K) Fig. 1. Vapour
pressures
of CszRuO,,
Cs,MoO,
and CsBO,.
with the same technique [11.18]. The data can be represented by the equation given in table 3. The thermal functions derived from the infrared data were combined with the vapour pressure measurements and with thermodynamic quantities for Cs,MoO,(s) [ll] in a third-law calculation to give an enthalpy of sublimation at 298.15 K of (308.2 + 0.5) kJ mol- ‘, which is in good agreement with that reported by Johnson [12] [(309.6 + 1.1) kJmolP’], and, to a lesser extent, with that of Tangri et al. [13] [(312.4 f 0.4) kJmolP’]. Finally, this value was used to calculate the enthalpy of formation of CszMoOq(g); A,Hk(Cs,MoO,, g, 298.15 K)= -(1206.3 i 1.5) kJmol_-‘. 3.2. Cs2Ru0,(c/g) The enthalpy of formation of Cs,RuO,(s) termined by means of solution calorimetry,
was deusing 1.0
of selected fission product compound.s
moldm ’ NaOH as the solvent [14]. To derive the cnthalpy of formation of the compound, the measured cnthalpy of solution was combined with the enthalpies of solution of CsOH(s) and NaBr(s) in the same medium and with data for the enthalpies of formation of CsOH(s), NaBr(s) and NaOH(sln). The enthalpy of formation of Cs,RuO,(s) at 298.15 K was found to be: A,H;(Cs,RuO,, s. 298.15 K) = -(964.6 F 5.3) kJmol_‘. Differential scanning calorimetry was employed to study the phase transitions in this compound. A transition was found at (906.8 & 0.4) K with an enthalpy of transition of (2.78 + 0.13) kJ mol- ‘. The melting point was found to be (1211.8 & 0.3) K, with an enthalpy of fusion of (27.11 i 0.53) kJ mol- ‘_ Low-temperature heat capacities for Cs,RuO,(c) were measured from 5 to 350 K using adiabatic calorimetry. From these measurements, the heat capacity and standard entropy, at 298.15 K. were derived, their values being 156.31 and 263.07 Jmol ’ K ‘, respectively. High temperature enthalpy increments were also measured, leading to the expression given in table 4. The vapour pressure of Cs,RuO, was measured in oxygen between 1015 and 1134 K using the transpiration method [ll]. The results are shown in fig. 1 and can be represented by the equation given in table 3. Molecular parameters for the Cs,RuO,(g) molecule were cstimatcd by analogy with Cs,MoO,(g) and are given in table 2. These data were used to calculate the thermal functions for Cs2RuO&g) which were combined with the vapour pressure measurements in a third-law calculation of the enthalpy of sublimation at 298. IS K, which was found to be (249.7 + 1.5) kJ moi ’ This was then used to calculate the enthalpy of formation of CszRuO,(g) at 298.15 K: A,H&(Cs,RuO,. g. 298.15 K) = --(714.9 k 5.5) kJ mol ‘.
Table 3 Vapour pressure measurements Comoound Cs,MoO, “) &MOO, h, CsZRuO, CsBO, ” CsBO, ” “I Based on caesium
IO~(
p
/atm) = A + BAT/K)
A
B
- 14470.5+ 584.7 - 14229.3? 653.6 - 8307.7 + 139.4 -14159 i375 -12098 k689
12.038 * 0.507 11.850 f 0.567 X.292* 0.128 15.537 * 0.407 13.458f0.665
analyses. I’) Based on molybdenum analyses.
” Over solid. d’ Over liquid.
T range (K) 1117 to 1117 to 1015 to 867 to 997 to
1190 1190 1168 982 1087
A,,,,,H”(298.15 K) (Jmol-‘)
Ref.
308.4 f 0.5 308.8 f 0.5 249.7 i 1.5 270.8 rf-0.7 269.0 &0.X
[ItI [LII [Lll
iI81 [I81
-
R.G.J. Ball et al. / Thermochemistry of selected fission product
3.3. Cs, MnO,k)
85
compounds
of CsOH(c), the enthalpy of formation of Cs3P04 at 298.15 K was found to be: A,Hk(Cs,PO,, S, 298.15 K) = -(1910.9 & 1.5) kJmol-‘. Differential scanning calorimetry was used to study the phase transitions in this compound. A reversible phase transition was found at (868.6 k 0.5) K, with an enthalpy of transition of (4.75 + 0.15) kJ mol- ‘.
tion
Low-temperature heat capacity measurements (5 to 350 K) were made on Cs,MnO,(c) by adiabatic calorimetry [15]. The heat capacity and standard entropy, at 298.15 K, were 155.0 and 240.6 Jmol-’ K-l, respectively. High-temperature enthalpy increments were also measured, leading to the expression in table 4. Cs,MnO, is isostructural with Cs,RuO, and has a phase transition in the solid state. Differential scanning calorimetric measurements showed this transition to be at (1052.0 + 5.0) K, with an enthalpy of transition of (0.59 + 0.08) kJ mol-‘. The melting point was determined as (1176.7 +_2.0) K. However, due to a reaction with the container materials, the enthalpy of fusion could not be measured. By comparison with the values for Cs,CrO,, Cs,MoO,, Cs,RuO, the enthalpy of fusion was estimated to be (21.0 k 0.5) kJmol_‘. The enthalpy of formation of Cs,MnO, was determined by solution calorimetry, using an aqueous solution of 4.032 moldmm3 H,SO, with 0.106 moldm-3 FeSO, as the solvent. The value at 298.15 K is: AfHk(Cs,MnO,, s, 298.15 K) = -(1179.5 + 3.0) kJmol_‘.
3.5. Cs,Si,O, The enthalpy of solution of Cs,Si,O, in HF(aq) was measured at 298.15 K [16]. By combining this value with the enthalpies of solution of a (SiO, + CsF) mixture in the same solvent, the enthalpy of formation was calculated to be: ArH&(Cs,Si,O,, s, 298.15 K) = -(4297.6 + 5.4) kJ mol-‘. The enthalpy increment of this compound was measured from 475 to 825 K, and the results are shown in fig. 2. By fitting the results to a polynomial with C&298.15 K) = 239.0 J K- ’ mol- ’ as a boundary condition, the expression given in table 4 was obtained. 3.6. Cs, ZrO,(c) The enthalpy increments of Cs,Zr03 from 451 to 641 K were measured, as shown in fig. 2. No measurements were made above 641 K due to reaction with the container material. Fitting of the results with C&298.15 K) = 126.0 JK-’ mole1 as a boundary condition gave the expression in table 4. The enthalpy of formation at 298.15 K of this compound, as reported by Cordfunke
3.4. Cs,POJc) The enthalpy of solution of Cs,PO, was measured in an aqueous solution of 0.034 moldmm3 H,PO,. Combined with the enthalpy of solution of CsOH measured in the same medium and the enthalpy of forma-
Table 4 Calorimetric
data
Compound
Cs,RuO,(s) Cs,MnO,(s) Cs,Si,O,(s) Cs,ZrO,(s) CdI &I CdI,W Cs,CdI,(s) Cs&dI,(s) Cs,CdI,(I) a) Enthalpy b, Enthalpy ‘) Enthalpy
A,H” (298.15 K) (kJ mol-‘)
- 964.6 + - 1179.5 f - 4297.6 + -1584.8+1.9 - 205.3 + _ a) b, ‘) increments increments increments
S (298.15 K) (Jmol-‘Km’)
5.3 3.0 5.4 0.9
- 920.3 + 1.4 _
for temperatures for temperatures for temperatures
263.07 240.60 313.00 200.00 157.61 _404.00 _
H(T)-
H(298.15
K)= ACT/K)+
B(T/K)’
+ C/CT/K)+
D
(JmolF’K-‘1 A
B x lo3
129.5580 99.8760 367.1725 167.3315 69.4374 111.1932 404.2505 231.0000 250.0000
44.8631 88.3800 0.50538 - 2.6252 13.5714 _ - 126.2530 _
up to 400 K. between 400 and 704 K. between 704 and 1000 K.
_
c x10-s
- 1.858 - 114.205 35.954 _ 120.76 _
D - 42616.00 - 37011.00 - 147822.00 - 61715.50 - 21909.20 - 23309.70 - 149807.30 - 67367.61 - 44043.61
X6
R.G.J. Ball et al. / Thermochemistry
300
LOO
500
600
700
800
TIK
Fig. 2. The reduced
enthalpy increment of solid Cs,Si,O,j and Cs,ZrO, (0).
(o)
et al. 1171, is: A,H$Cs,ZrO,,
s, 298.15 K) = -(1584.8 f 1.9) kJmol_‘, and an estimated value for the standard entropy at 298.15 K is 200.0 JK-’ mol I.
3.7. CsBO,(g)
The gas-phase vibrational spectrum of CsBO, was studied from 25 to 3000 cm-’ at a resolution of 0.5 cm -‘. Four major absorptions were observed in the range from 3000 to 375 cm-’ at 1933, 1045, 632 and 588 cm- ‘. Between 350 and 25 cm- ‘, only one absorption was found, at 232.8 cm-‘. The intensities of the peaks increased with increasing temperature, implying that they can be attributed to C&O, species. The bandwidth also increased with increasing temperature and at 1390 K, it was difficult to discriminate between the 632 and 588 cm- ’ peaks. Minor absorptions were observed at 1190 and 1385 cm-‘, but the intensities of these peaks increased with time rather than with temperature. It was concluded that these peaks arose from condensation of the vapour species in the cell atmosphere and on cell windows. Solid CsBO, exhibits its strongest absorptions at 1183 and 1379 cm-’ at room temperature. The peaks in the gas-phase infrared spectrum could be assigned on the basis of a bent molecule with a linear O-B = 0 group. Matrix isolation infrared spectra were also measured for CsBO,. The mid-infrared (2500 to 400 cm-‘) spectrum of the vapour was dominated by doublets at 1956/2026 and 575/594 cm-‘. A third, weaker doublet was also observed at 1073/1080 cm-‘. The intensity ratio of the two components was 4 in all three doublets and this is indicative of the presence of natural boron (20% ‘“B, 80% “B). The peaks in the matrix
of selected fission product compounds
infrared spectrum correspond to those in the gas-phase spectrum, apart from the absence of an analoguc to the gas-phase frequency at 632 cm ‘. However, a shoulder was observed on the 574 cm ’ band at 579 cm- ‘. The low frequency region of the spectrum (400 to 30 cm- ’ ) contained bands at 336 and 300 cm ‘. A very weak band at 205 cm-’ was also observed which was assigned to the Cs-0 stretching mode of CsBO?. The gas-phase frequencies were used to calculate the thermal functions for CsBO, over the temperature range 298 to 3000 K. The molecular parameters are given in table 2. The equilibrium vapour pressures over both solid and liquid CsBO, were measured by means of the transpiration method [18]. If it is assumed that only gaseous monomeric species are present. as indicated by mass spectrometric results [19], then the vapour pressure over solid and liquid CsBO, can be represented by the equations given in table 3. A third law calculation based on these vapour pressure measurements gave the cnthalpies of sublimation also given in table 3. The slight difference in the values derived for the solid and liquid data may be due to the fact that the thermodynamic parameters arc less accurately known for liq-. uid CsBO, than for the solid.
4. Iodides The interest in the iodides of indium and cadmium arise from the potential reactions between fission product iodine with control rod material [7]. In this work, the vaporization behaviour of indium and cadmium iodidcs was studied by mass spectrometry and matrix isolation infrared spectroscopy. In addition, critical assessmcnts of thermodynamic properties of the vapour phase indium iodides were carried out. The formation of ternary caesium-cadmium-iodine compounds, such as Cs?CdI,, in the primary circuit has been postulated to occur as a result of the reaction of caesium iodide with cadmium or cadmium iodide aerosol, according to 2CsI(g)
+ CdI,(s,
I) --j Cs,CdI,(s,
I).
Such reactions could result in changes in the volatilities of fission product iodine and caesium. Evidence for reactions of this type can be found in experimental studies of the interaction of caesium iodide vapour with aerosols generated from control rod alloy samples [20]. Hence, in this work, the CsI-CdI, phase diagram was studied using differential thermal analysis to identi@ and characterize the possible condensed phase compounds.
87
R.G.J. Ball et al. / Thermochemistry of selected fission product compounds
and eventually to In1 and I, occurs. The observed infrared frequencies for InI, InI, and In,I, were combined with other molecular constants in the literature (see table 2) to calculate the thermal functions for the molecules. For InI( S”(298.15 K) was calculated to be 267.34 J K- ’ mol-’ and C&298.15 K), 37.11 JKP1mol-‘. For InI,( the values were: 400.34 J KP ’ mol - ’ and 80.99 J K- ’ molt ‘, respectively, and for In,I,(g), 637.00 J K-’ mol-’ and 178.76 J K- ’ mol- ‘, respectively. A critical assessment of the enthalpies of formation of the vapour phase indium iodides was carried out. There are five recent determinations of the vapour pressure of InI, one for the solid from 470 to 557 K [24], and four for the liquid, from 640 to 1010 K [25], from 640 to 773 K [26], from 638 to 1015 K [27] and from 646 to 958 K [28]. As shown in fig. 4, there is excellent agreement between these studies, except for the less precise values of Federov et al. [26], and the extrapolated lines for the solid and liquid intersect within the known range of the melting point 624-638 K. All the studies involving In1 stress the difficulty of preparing InI free from higher iodides and the higher vapour pressures measured by Federov et al. [26] probably result from such impurities. This is presumably also true for the early study by Robert [29] which gives pressures higher than those in fig. 4 by about a factor of four. The analysis of the vapour pressure data by the third law method is summarized in table 5. The selected value for the enthalpy of sublimation of In1 is InI,
b
Wavenumber
i cm-‘1
Fig. 3. Argon matrix infrared spectra from indium tri-iodide vaporization at 390 K. (a) No superheating, (b) vapour superheated to 770 K, (c) vapour superheated to 970 K.
4.1. In-l
Matrix isolation infrared studies of the vapour at 400 K gave a more complicated spectrum than that expected for InI, molecules, see fig. 3. Four bands were observed at 231, 180, 160 and 124 cm-‘. These could be assigned to the infrared-active In-I stretching modes of the dimeric molecule In,I, and are close to those reported for solid phase indium(II1) iodide [21,22], which consists of discrete In,I, molecules. On superheating to 770 K, the intensities of the four dimer bands decreased and the spectrum was dominated by a single band at 236 cm-l (see fig. 3). This was assigned as the asymmetric In-I stretching frequency of a planar InI, molecule. At 970 K, this band also decreased in intensity and a new, sharp band at 167.7 cm-’ became the dominant feature. This latter frequency was assigned to InI, though it is shifted somewhat from the gas-phase value for this molecule (177 cm-’ [23]). Such a shift is not uncommon for matrix-isolated molecules with a significant dipole moment, as expected for InI. Thus, the vaporization of indium(II1) iodide at low temperatures yields In,&, but as the temperature of the vapour increases, dissociation to
1
-5 -6 -
= Barrow et al. [24] 0 Brumleve et al. c281 + Grinberg et al. c251 x Chusova et al. [271 0 Federov et al. C261
-7 - -Assessed -8. 0.9
I 1.1
data I 1. 3
I 1.5
I 1.7
I 1.9
IO3 I T IK-‘1
Fig. 4. Vapour pressure of InI.
I 2-l
I 23
xx
R. G.J. t3dI
et al. /
of’selected fi.s.siorr product
Thennochetni.stry
c~m1po~m1.s
Table 5 Vapour pressure studies for InI(g) -__ References
T(mean) (K)
Smith and Barrow [%I Grinberg et al. [25] Chusova et al. [27] Brumleve et al. [2X]
525 825 x75 X02
log ,,,p /atm .4/T+R
=
il
H
~ 0565.6 5290.0
7.230 5.210
(129.0-t 1.5) kJmol ‘. This lcads to: L,N;(lnl. g. 298.15 K) = 26.5 kJ mol ‘. This is somewhat more positivc than that derived from the dissociation cncrgy at 0 K of 3.43 CV given by Huber and Herzbcrg [30]. Correction to 298.15 K gives 333.0 kJ mol ’ for the dissociation enthalpy to In and I gases, which with enthalpies of formation of 240.4 [3 1] and 106.8 kJ mol ’ [32] respectively, gives an enthalpy of formation for In1 (g) of 14.1 kJmol I. Presumably In(g) or I(g) is in an excited state in this dissociation. The cnthalpies of formation of InI, and In,I,(g) arc not easy to define since. as shown earlier, although InI, is quite volatile, both monomer and dimcr occur in the gas phase, even at low tcmperaturcs, while above 650 K, dissociation to InI and perhaps also divalent iodides InI, and/or InlI,(g) occurs. Howcvcr, the cnthalpies of formation for thcsc species wcrc derived as follows. The studies of the reaction InI,
--f InI
+ I,(g)
by Titov and Chusova [33]. Zaidova et al. 1341 and Grinberg et al. [35] wcrc analyscd to provide A, Hi,(InI,, g). This was then combined with data for the dimerization reaction 2Inl,(g)
+ In,I,,(g)
to obtain AfH,“,(In,l,,. g). The values obtained for the enthalpics of formation were: AfHi,(InI;. g, 29X.1 K) = -(104.0 F 4.0) kJmol_ ’ and A,Hz,(Inz16, g. 298.15 K) = -(326.0 i 12) kJmol ‘. In the final optimization, thcsc cnthalpics of formation were used and the standard entropy of InI, adjusted to give rcasonable agreement with the vaporization information from Smith and Barrow [36]. Fcderov et al. [37] and Girichcva ct al. [3X]. With a value for S(In1,. c, 29X.15 K) of 222.0 + 10 J K ’ mol ‘, good agreement was obtained with ai the data cxccpt for that of Fcderov et al. [37]. which has internal inconsistencies in the published data: even there, agreement was probably within cxpcrimcntal error. The correct boiling point of 773 K was obtained by selecting the reasonable value of IX.3
AS(exp)
AS(calc)
13-L-I
137.5 137.5
97.1
-. A,,,,,11(2YX.l5 K) third Ia\\
179.7 t I.?
IXJ.0t- 0.r;
kJ mol ’ for A,,,,H(4XO IO, in tolcrahlc agrccmcnt with the preliminary value of 14 kJ mol ’ mcasurcd bb Ncwland 1391. ‘!.‘?. (‘d-i Previous studies of cadmium iodide by mass spcctromctry have shown that the predominant spccics i\ monomeric Cdl, [40]. However, studies have also indicated the prescncc of small amounts of polymeric (probably dimcr) species [41]. The matrix isolation infrared spectrum of cadmium iodide vapour was dominated by a peak at 265.7 (Ar matrix) or 260.9 cm ’ (N, matrix) with a much weaker peak at 49.7 (Ar matrix) OI49.2 cm ’ (N, matrix). Additional bands at 217.7 and 153.6 cm ’ were assigned to polymeric species formed in the matrix since the intcnsitica of the features rcla-tive to the main peak varied under different deposition conditions. The measured frequencies were combined with a previously-reported Raman frequency for the infrared-inactive totally symmetric stretching mode (155.1 cm ’ [42]) and a value for the Cd-1 bond length of 0.255 nm [43] in order to calculate the thermal functions for the molcculc (see table 2). In the condensed phase, the cnthalpy incrcmcnts ot solid as well as liquid CdI, wcrc measured from 477 to X59 K. The data were fitted to polynomials, one for the solid phase (29X.1.5 to 654 K) and one for the liquid phase as shown in table 4. For the solid phase. the boundary condition, C&298.15 K) = 77.53 J K- ’ mol ’ was used during the fitting procedure. The cnthalpy ot solution at 29X.15 K of CdI.(s) in H,SO, was mcasured. By combining the resu?ts with the cnthalpies ol solution of CdO, KI and K,SO, in the same medium. the cnthalpy of formation of the compound was found to bc S,H;(CdI,, s. 29X.15 K) = -(205.3 + 0.0) kJ mol ‘. Differential scanning calorimetric mcasuremcnts were cmploycd to dctcrmine the melting point of Cdl,. This was found to be at (654 & 2) K. From the cnthalpy
R.G.J. Ball et al. / Thermochemistry of selected fission product compounds
The heat capacity, enthalpy change for the solid state transition and enthalpy of fusion for Cs,CdI, were determined by means of differential scanning calorimetry. The heat capacity data were fitted to polynomials in temperature, as given in table 4. The enthalpy change for the solid state transition was 3150 Jmol-‘, while the enthalpy of fusion was 36.7 kJmol_‘, with an uncertainty of 1% in the data. The enthalpy of formation of Cs,CdI,(s) was determined by solution calorimetry using H,SO,(aq) as the solvent. The value obtained was A,&(Cd,CdI,, s, 298.15 K) = -(920.3 f 1.4) kJmol_‘. The only previous value for the enthalpy of formation of this compound, - (916.6 k 3.5) kJ mol-’ was reported by Auffredic and Touchard [45], who measured the enthalpy of solution of Cs,CdI,(s) in water. Recalculating their thermochemical cycle with the same auxiliary data for CsIW and CdI,(s) used in this study gives a value for the enthalpy of formation of -(917.7 + 1.5) kJmol_’ which is in reasonable agreement with the present result.
increment equations for solid and liquid CdI,, the enthalpy of fusion is calculated to be 20.10 kJmoll’. 4.3. Cs-Cd-I The CsI-CdI, phase diagram was studied using differential thermal analysis. As shown in fig. 5, the only compound observed in these studies was Cs,CdI, with a melting point of (702 k 1) K. Two phases (a and p) of this compound were observed and positively identified by hot cell X-ray diffraction. The transition between the two phases was found to be reversible. However, unlike the (Yto l3 transition, which was fast, the p to cx transition required in excess of 14 days for completion, in agreement with earlier observations by Touchard et al. [44]. The temperature of transition depended on the composition: the transition occurred at 430 K in excess CsI, compared with 400 K for the pure compound, implying that the large Cs+ ions were more readily accommodated in the a-Cs$dI, lattice.
3
600 -
0
20
89
40
Fig. 5. CsI-CdI,
60
phase diagram.
80
00
R.G.J. Bali et al. / Thermochemistry
5. Conclusions Experimental studies and critical assessments have been undertaken to obtain thermochemical data for selected compounds of fission products and reactor materials. The choice of compounds was based on the recommendations of a specialists’ meeting held at JRC-Ispra, Italy in 1990 [4]. In this report, a selection of results from the study were presented. The work carried out represents a significant improvement in the thermodynamic database for reactor materials and fission products and will permit a more comprehensive assessment of the fission product source term to be made. This will enable the consequences of a severe accident in a nuclear plant to be predicted with greater confidence on a mechanistic basis.
Acknowledgements The authors wish to thank A.L. Nichols, M.S. Newland, J.S. Ogden, P.E. Potter, I.R. Beattie, E.F. Westrum, Jr., M.H. Rand, J. Drowart and C.A. Alexander for helpful discussions associated with this work, M.S. Newland, J.S. Ogden, N.E. Freemantle, V. Smit-Groen, W. Ouweltjes, R. v.d. Laan and A.S. Booij for assistance with the experimental work, and S.J. Wood and B.A. Bellamy for analytical chemistry support. The Dutch work was funded in part by the Commission of the European Communities, Joint Research Centre, Ispra (Research Contract No. 38768912 EL ISP NL). The UK studies were funded by the Commission of the European Communities, Joint Rcsearch Centrc, Ispra (Research Contract No. 3871-89. 12 EL ISP GB), the UK Health and Safety Executive (PWR task SAA 3.1), the General Nuclear Safety Programme (task FPB5), and the AEA Corporate Research Programme.
References [II T.J. Heames, D.A. Williams. N.E. Bixler, A.J. Grimley. C.J. Wheatley, N.A. Johns and N.M. Chown, VICTORIA: A Mechanistic Model of Radionuclide Behaviour in the Reactor Coolant System Under Severe Accident Conditions, Sandia National Laboratory Report for US Nuclear Regulatory Commission, NUREG/CR-554s (1990). [?I R.G.J. Ball, B.R. Bowsher, S. Dickinson, E.H.P. Cordfunke, R.J.M. Konings and M.H. Rand, Thermochemical Data Acquisition, Commission of the European Communities Report, EUR 14004 EN (1991).
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E.H.P. Cordfunke and R.J.M. Konings, Thermochemical Data Acquisition, part II. Netherlands Energy Research Foundation ECN, Report No. ECN-C-92-033 (1992); to he published as Commission of the European Communities EUR-report. in Severe I41 AL. Nichols, ed., Fission Product Chemistry Nuclear Reactor Accidents, Specialists’ Meeting at JRCIspra, IS-17 January 1990, UKAEA Report, AEA-TRS5024 (1990) and Commission of the European Communities Report, EUR 12989 EN (1990). [51 J.K. Fink, M.F. Roche. C.A. Seiis. D.V. Steidl, and C‘.t. Johnson, Proc. ACS Symp. on Chemical Phenomena Associated with Radioactivity Releases During Severe Nuclear Plant Accidents, NUREG/CP-0078 (1986). [61 B.R. Bowsher, Prog. Nucl. Energy 20 (1987) 199. [71 R.M. Elrick, R.A. Sallach, A.L. Ouellette and S.C. Douglas, USNRC Report NUREG/CR-3197, vol 1 (lYX4). [81 V.V. Ugarov. Y.S. Ezhov and N.G. Rambidi, J. Mol. Structure 25 (1975) 2140. L. Bencivenni and K.A. Gingerich, J. [91 H.M. Nagarantha, Chem. Phys. 81 (1984) 591. [lOI A.A. Belyaeva, M.I. Dvorkin and L.D. Shecherba. Opt. Spectrosc. 38 (1975) 170. [III EJ1.P. Cordfunke, R.J.M. Konings and S.R.M. Meysscn. J. Chem. Thermodyn. 24 (1992) 725. [I21 I. Johnson, J. Phys. Chem. 79 (1975) 722. 1131 R.P. Tangri, V. Venugopal, D.K. Bose and M. Sundaresari,, J. Nucl. Mater. 167 (1989) 127. R.J.M. Konings, W. Ouwekjes and P. 114J E.H.P. Cordfunke, van Vlaanderen, J. Chem. Thermodyn. 22 (1990) 285. and E.F. Westrum, Jr.. to he pub[lSl E.H.P. Cordfunke lished. Llhl E.H.P. Cordfunke and W. Ouweltjes. to be published. [I71 E.H.P. Cordfunke. W. Ouweltjes and P. van Vlaanderen, J. Chem. Thermodyn. 19 (1987) II 17. [I81 E.H.P. Cordfunke, R.J.M. Konings and S.R.M. Meyssen. J. Chcm. Thermodyn. 23 (lY91) 297. A.V. Gusarov. A.V. Makarov and 0.7’. [191 L.N. Gorokhov. Nikitin, Teplofiz. Vys. Temp. 9 (1971) 1173. [201 A.M. Beard, C.G. Benson and B.R. Bowshcr, UKAEA Report AEEW-R 2470 (I 988) [211 D.M. Adams and R.G. Churchill, J. Chem. Sot, (A) (I(3683 2141. 1221 I.R. Beattie. T. Gilson and G.A. Ozin. J. Chem. Sot. iA) (1968) 813. [231 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds (Wiley. New York. 197X). I241 R.F. Barrow, A.C. Pugh and F.J. Smith, Trans. Farad. sot. 51 (195.5) 1657. [251 Y.K. Grinberg, V.A. Boryakova, V.F. Shevel’kov and Z.S. Medvedeva, Izv. Akad. Nauk SSSR Neorg. Mater. X (lY72) 07. [261 P.1. Federov, N.S. Malova and Yu.N. Denisov. Russ. J. Inorg. Chem. 21 (1976) 640. [271 T.P. Chusova. N.I. Matskuvich. Yu.G. Stenin and (;.A. Kokovin. Jzv. Sib. Otd. Akad. Nauk. SSSR. Ser. Khim. Nauk. 5 (1979) 62.
R.G.J. Ball et al. / Thermochemistry of selected fusion product compounds [28] T.R. Brumleve, S.A. Mucklejohn and N.W. O’Brien, J. Chem. Thermodyn. 21 (1989) 1193. [29] G. Robert, Helv. Phys. Acta 9 (19361 405. [30] K.P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, vol. IV, Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 19791. [31] V.P. Glushko et al., Thermodynamic Properties of Individual Substances, vol. II (Akademy Nauka, Moscow, 19811. [32] J.D. Cox, D.D. Wagman and V.A. Medvedev, CODATA Key Values for Thermodynamics (Hemisphere, New York, 1989). [33] V.A. Titov and T.P. Chusova, Isv. Sib. Otd. Akad. Nauk. SSSR, Ser. Khim. Nauk. 1 (1987) 75. [34] G.A. Zaidova, S.M. Gadzhiev and A.A. Kuliev, Russ. J. Inorg. Chem. 48 (1974) 617. [35] Y.K. Grinberg, V.A. Boryakova and V.F. Sheve’kov, Isv. Akad. Nauk. SSSR Neorg. Mater. 12 (1964) 551. [36] F.J. Smith and R.F. Barrow, Trans. Faraday Sot. 54 (1958) 827.
91
[37] P.I. Federov, A.G. Dudareva and N.F. Drobot, Russ. J. Inorg. Chem. 25 (1963) 1739. [38] N.I. Giricheva, V.M. Petrov, B.V. Girichev, V.A. Titov, T.P. Chusova and G.A. Kokovin, Isv. Sib. Otd. Akad. Nauk. SSSR, Ser. Khim. Nauk. 3 (1986) 23. [39] MS. Newland., AEA Technology, Winfrith, private communication (1989). [40] S. Dickinson, UKAEA Report AEEW-R 2227 (1987). [41] L. Topor and I. Moldoveanu, Rev. Rom. Chim. 19 (1974) 985. [42] A. Strull, A. Givan and A. Loewenschuss, J. Mol. Spectrosc. 62 (1976) 283. [43] P.A. Akishin and V.P. Spiridinov, Kristallographia 2 (1957) 475. [44] V. Touchard, M. Louer and D. Louer, Powder Diffr. 1 (1986) 35. 1451 J.P. Auffredic and V. Touchard, Thermochim. Acta 162 (1990) 463.