Thermochemical data for reactor materials

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Nuclear energy and safety
Energy research

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 47
• Langue: Serbian
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Commission of the European Communities
nuclear science
and technology
>
Thermochemical data
for reactor materials Commission of the European Communities
nuclear science
and technology
Thermochemical data
for reactor materials
C. Ronchi, F. Turrini
Commission of the European Communities
Joint Research Centre
Karlsruhe Establishment
European Institute for Transuranium Elements
D-75 Karlsruhe
Directorate-General
Science, Research and Development
Joint Research Centre
1990 EUR 12819 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then is responsible for the use which might be made of
the following information
This document has been reproduced from the best original available
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1990
ISBN 92-826-1558-8 Catalogue number: CD-NA-12819-EN-C
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1990
Printed in Belgium CONTENTS
Page
INTRODUCTION 1
THE F.P. CHEMISTRY IN THE RELEASE CODES 3
The original input
The new input Λ 5
Remarks 6
Collecting the data
Source file structure 7
Data structure
ADDITIONAL DATA AND DISCUSSION 22
SOURCES 2
REMARKS ON THE CHEMICAL EQUILIBRIUM CALCULATIONS
The expression of the specific heat4
The specific heat of the liquid
Error evaluation6
EXPLANATION OF THE TABLES7
PROPERTIES OF THE COMPOUNDS 2
Uranates and molybdates
Other rompounds8
TABLES OF P'ERMOCHEMICAL DATA AND & "LOTS 33
REFERENCES 185
— III INTRODUCTION
The objective of the work reported here is to extend and organize in a computer database
the set of thermochemicaf data for reactor materials and fission products collected by
Cordfunke and Potter (C.P.) 11/ in the framework of a research contract supported by the
Commission of the European Communities. In this context, at the JRC Karlsruhe a work
was started aimed at constructing a computer file to be accessed by existing codes for the
calculation of the radiological consequences and, in particular, of the source term in Light
Water Reactor accidents.
The data presented here pertain to compounds formed by the chemical elements of fuel
(uranium oxide), fission products and structural materials and were obtained from avail­
able large databank or reviews.
A serious problem encountered in using these data is the assessment of the errors and
confidence limits, since since they depend on two sources: First on imprécisions and
possible inconsistencies of the experimental data, second on the extrapolation procedure
which was in most cases applied to obtain high temperature data. On the other hand, in
reactions where only solids and liquids take part, if the Kopp­Neumann rule is valid, the
heat capacity difference in the reaction is effectively zero and therefore only the enthalpy
of formation ΔΗ298 may be effectively needed for equilibrium calculations. For this reason
the enthalpies of formation and entropies at 298 Κ for the various compounds have been
separately collected with an estimation of their accuracy. The sources are there JANAF,
NBSTHERMO, Barin and Knacke (B.K.) 12,31 and Kubaschewski and Alcock (K.A.) 141. A
more detailed discussion of this point is presented in the following sections.
The data reported in ref. 111 and those contained in this report have been stored in an
input file of the computer code MITRA 151 which calculates the release and chemical
reactions of the radioactive fission products in nuclear fuels. The chemical equilibrium is
evaluated with a modified SOLGASMIX module. This subroutine calculates the chemical
equilibrium starting from the Gibbs formation energies of the given compounds. In order
to avoid storing a large number of tabulated values which involve in any case temperature
interpolations, AGf was expressed as a linear function of temperature in distinct T­inter­
va/s. These are reported in the graphs which follow the tables of each compound. The
slope and the y­intercept of each line is indicated for the various segments. These plots
are the result of the linear regression analysis of the free energy data presented in the
tables. In most cases they are indeed their exact representation as the tabulated data
were often also obtained by a linear fitting. Only in special cases approximations have
been made to prevent information from becoming cumbersome; these are however inin­
fluential.
­ 1 ­The compounds are listed in alphabetical order and every item is presented in the fol­
lowing state sequence: crystal, liquid, gas, when of course the respective data are avail­
able. Temperatures at which phase transformations occur have been always taken as an
extremity of a AG segment.
The meaning of the various thermodynamica! quantities does not need particular com­
ments. Their definition are as follows:
Enthalpy of formation
AH = ΔΗ2981 .15 + + j ACpdT
J298.1 15 i
Entropy of formation
AS = AS29815 + . -f-dT
298.15
Gibbs free energy of formation
AG = AH - TAS
Gibbs free energy function
GEF = -(G{T)-H29a.,5)/T
where Cp is the specific heat at constant pressure.
Finally, it should be remarked that, except for a few cases, the AG values for the gas
phases are given for a pressure of 0.1 M Pa and in most cases the perfect gas rule is
assumed. Extrapolation at very high pressures, as it is often required in reactor safety
calculations, should be made with caution. THE F.P. CHEMISTRY IN THE RELEASE CODES
The code MITRA (Multicomponent Isotope TRAnsport), in progress at the JRC Karlsruhe,
calculating the redistribution and release of radioactive fission products in nuclear fuels,
has been coupled with the code SOLGASMIX-PV 1241, a slightly modified version ofSOL-
GASMIX 1221, which calculates equilibrium compositions in systems containing one gase­
ous phase, condensed mixtures, and condensed phases of invariant or variable stoi-
chiometry.
In order to use SOLGASMIX-PV as a subroutine of MITRA a new input procedure was
created whose runnings are disengaged from the manual building of the cumbersome
original input matrix.
A thermodynamics data bank was therefore constructed for the species which may
involved in the chemical equilibrium required by MITRA, and an interface program
between that database and SOLGASMIX.
At the moment, this database, named BANCA.DIR, contains approximately 150 species.
Nevertheless, a large difference still exists between the number of possible species
formed by the elements present in the MITRA data bank, and that formed by the elements
contained in SOLGASMIX one.
A crucial problem remains the modelling of chemical reactions which could represent
in an adeguate way the complex system. The treatment of the various phases that can
occur at the reactor accident temperature conditions can be made only by a judicious
choice of the constituents and a deep knowledge of the thermochemical properties of the
involved compounds.
In this section we give a description of:
• the modifications made on the SOLGASMIX input procedure;
• the database BANCA.DIR structure and content;
• the use of computer programs created to store and manage the data.
The Original Input
Table I shows an example of the structure of the original SOLGASMIX input with a
chemical system based on eleven elements and sixty species. Leafing through this, one
can realize what kind of enterprise one has to pursue each time new chemical conditions
are to be analyzed. The main parameters affecting the dimensions of the input file are the number of ele­
ments and species. A set of conditions describing the input system is defined as a generic
combination in the vector
{...elements species...} (1)
where with 'species' is meant a list of compounds and elements ordered according to the
initially existing phases and mixtures.
In the input file we distinguish four different kind of lines respectively referring to:
1 - a description of the chemical system: number of elements, mixtures, species for mix­
ture, element reference state and their symbols;
2 - a coefficients matrix Amn where
- m, is the number of rows/species
- n, is the of columns/elements in the system. The elements of the matrix
[A] are the stoichiometric coefficients of the species;
- a coefficients matrix Bmi where 'I' is either the number of coefficients considered in the
Free Energy of Formation expression
AG°f = a/T+b + cT+dT2 + eT3 + fT\n(T) for ΤΛ<Τ<Τ2 (2)
or 1 = 2 if the Free Energy Functions and Entalphy of formation for each species are used.
3 - a description of the temperature, pressure, volume conditions in which the system is
supposed to be;
4 - a vector {C„} containing the total amounts of each element in its chosen reference
state.
Using the introduced notation we can say that the thermochemical properties of