• Relap5/Mod3.3
• Equation of state
• Hitec
• Lead-Lithium
• Nuclear Fusion

The present thesis work discusses the models to evaluate the thermodynamic properties of two candidate working fluids for nuclear fusion applications: Lead-Lithium (PbLi) and HITEC molten salt.
Aiming at the role of breeder material of nuclear fusion concepts such as ITER TBM and DEMO, Lead-Lithium is an alloy: 83 mol% Lead, 17 mol% Lithium. Possible alternative is the ternary molten salt made by 7 mol% NaNO3 - 49 mol% NaNO2 - 44 mol% KNO3, with commercial name HITEC.
. For both coolants, current reference literature presents only a limited set of data, specifically restricted to constant pressure equal to the atmospheric value.
An additional objective of this work was to extend such properties data to the whole multi-phase region by results of either a model or a more general equation of state (EOS). This requirement makes possible the implementation of said coolant properties in system thermal hydraulic codes as RELAP5/Mod3.3.
No previous general EOS was available for HITEC in the literature, while for PbLi a reference EOS was available by Idaho National Laboratory.
Numerous have been the challenges to overcome to deliver a valid solution to the problem.
First, experimental data have been analysed to produce needed saturation pressure laws as a function of temperature. Starting from single components, the result for the mixtures has been obtained.
Even the simplest model required an estimated value of critical temperature, therefore further challenge consisted into solving non-linear least-square minimization problems.
Once identified the starting point, with experimental laws and a simplified model, efforts have been performed to obtain an equation of state for both candidate fluids.
Quest begins with a trial cubic equation of state for HITEC. Water was used as benchmark to test the code implementation and to show the limits of the EOS under examination. Results proved that this method was ineffective for fluids of interest.
Next, a promising multi-parameter EOS is presented. Water benchmark problem is solved once again to show the improvements compared to a simpler cubic EOS. Due to a lack of necessary data, specifically saturated specific volumes as a function of temperature for the fluids of interest, this model is dropped and left as an open point for further development once those functions would become known.
Finally, new equations of state are obtained developing an all-new method that implements vapor-liquid equilibrium starting from the well-known virial expansion.
As with other multi-parameter EOS, simultaneous multi-properties fit is performed: from an initial guess, final parameters allow to obtain all properties including saturation pressure from Maxwell loop construction.
Moreover, compared to other multi-parameter EOS known in literature, presented method allows for any set of parameters the existence of a single loop compared to multiple or none of other methods.
Implementation and comparison between evaluated EOS and reference one have been performed and results presented for PbLi.
Comparison between experimental results and evaluated ones shows good matches for all PbLi properties and for most HITEC properties – for the latter only the speed of sound result is overestimated.
Further improvements (here not discussed) would target the use of a better initial guess to the multi-fit problem, possibly using statistical thermodynamics.
Establishing the real critical point is a challenge that may require additional experimental data since all the properties used are considered for intervals of temperature very low compared to the expected critical temperature for liquid metals.
The performed work allowed to setup EOS for both the working fluids under examination and of interest in the nuclear field; the experimental validation is a logical next step that would be necessary for any further development.