The way forward
to the ultimate safe nuclear reactor

WP1 Integral safety approach and system integration
WP1 deals with the integral safety assessment and the overall reactor design including the chemical plant. First the initial reference design of the MSFR will be defined and documented including all updates and recommendations from the previous FP7 project EVOL. This will be a living document with continuous updates during the project based on new insights from the other work packages. From the reference design, safety related data on the physicochemical properties of the fuel salt and on the materials will be identified and passed over to WP2 for evaluation. CNRS will take the lead in the development of a MSFR power plant simulator. Together with CIRTEN they will analyze the dynamic behavior of the reactor, develop the main control strategies, and identify safety issues related to normal operation transients like start-up, shut-down, load-follow operation, etc. EDF will use its wide operational experience in the validation process of this simulator. IRSN and AREVA will take the lead in the development of an integral safety assessment methodology with theoretical/analytical contributions from CNRS and CIRTEN and using the wide experience from EDF. CIRTEN, in collaboration with CNRS and TU Delft, will lead an extensive risk assessment based on the integral safety approach to define all accident initiators and scenarios. AREVA, IRSN, and EDF will contribute to the methodology and to the identification of accident initiators and scenarios. The complete set of scenarios will be transferred to WP4 for a thorough and complete evaluation. Besides the fact that the analyses in WP1 will provide the input data for (mainly) WP2 and WP4, all other work packages will strongly interact with WP1 by providing more accurate data needed for the safety assessment and by giving strong recommendations to improve the reactor design. Proliferation resistance aspects will be included in this design and safety process from the beginning.

WP1 is the “director” of the top-down approach mentioned above, leading the integral safety assessment and coordinating the two-way data exchange with the other work packages delivering data and requests, and receiving data and recommendations. The strong involvement of the TSO and industry lays a sound base for the exploitation and dissemination of the safety methodology and for the acceptance of the safety principles of the MSFR by other TSO’s and the nuclear safety authorities.

WP2 Physical and chemical properties required for safety analysis
WP2 will experimentally determine all safety-related data of the fuel salt. JRC will synthesize and purify the PuF3 and UF4 containing salts, and will evaluate the phase diagrams by measuring new equilibrium data as well as the activities of the liquid phase components. Also the activities of fission products in the fuel will be measured. JRC and TU Delft will develop new experimental techniques and measure the thermal properties of the liquid salts, among which the viscosity, the melting behaviour, and the heat capacity. Using calorimetric methods, the JRC will examine the equilibrium data of the fuel salt and the first precipitates upon super cooling. The thermal conductivity of the solid crust possibly formed at the walls of piping and the freeze plugs, will be measured using the laser flash method. TU Delft will measure the interaction of simulated spent fuel salt with water also applying gamma radiation to get a better understanding of this effect on the salt solubility. JRC, CNRS and PSI will measure the retention properties of the fuel salt during a high temperature event. The focus will be on caesium and iodine, being the most volatile fission products in solid-fuel reactors. Study of the chemical form of tellurium with respect to the redox potential of the fuel salt will be performed. Finally, JRC will investigate the vaporization behavior of the fuel salt using the mass spectrometry technique until complete vaporization of the fuel. PSI will simulate the formation of aerosols by vapor-air interaction.

WP2 will deliver safety-related data of the fuel salt as input to other work packages (WP1, WP3, WP4) and will contribute to accident scenarios in which the fuel salt characteristics play an important role.

WP3 Experimental proof of i) shut‐down concept and ii) natural circulation dynamics for internally heated molten salt
WP3 will experimentally and numerically investigate the natural circulation dynamics of the fuel salt in the primary vessel and drain tanks, and the behavior of the salt in the freeze plugs during a drain transient. CIRTEN will modify the experimental loop DYNASTY to validate the theoretical models for natural circulation dynamics of the fuel salt, which is more complicated than with ordinary coolants due to the internal heating of the salt by fission product decay. The experiments will focus on the measurement of stability maps, on the effects of parallel channels (simulating the multiple heat exchanger loops in the primary circuit), and on the interference of two coupled loops (simulating an extra decay heat removal system in the primary circuit). CNRS will take the lead in determining the physical conditions during a salt draining transient and in the design of the freeze plug shut-down system. To this end, CNRS will design and build the SWATH experimental facility to investigate solidification phenomena of the salt along the walls of pipes and plates, to test various freeze plug designs, to measure heat transfer and flow phenomena as a function of the Reynolds number, and the effects of partial solidification on the heat transfer. TU Delft and EDF will support these tasks with numerical calculations for the design of the experimental facilities and the interpretation of the experimental results. The results of the experiments will be used to provide data to WP1 and to iterate on the final design of the MSFR.

WP3 will provide the proof of concept of the two key safety features of the MSFR using advanced experiments and calculations.

WP4 Accident Analysis
WP4 will numerically assess the accident scenarios identified in WP1. These include the normal operation transients and the off-normal accident scenarios. TU Delft will develop and extend its multi-physics simulation tools to address the unique features of the MSFR and to include the specific physics that may occur during transients such as freezing/melting phenomena and production and transport of gas bubbles in the salt. The verification and validation of this code package will be done on results from the previous FP7 project EVOL and on experimental results from WP3. The specific outcome of the simulations will be augmented with uncertainty quantification studies developed by TU Delft and CIRTEN, to propagate the effect of uncertainties in the input or model parameters on key safety parameters and to provide confidence intervals. For each of the detailed accident scenarios provided by WP1, TU Delft, and CIRTEN will generate three-dimensional power distributions and temperature fields as a function of time under a wide range of initial conditions determined by the steady state operation and the off-normal conditions. In particular the decay heat removal, and the natural recirculation abilities of the reactor under accident conditions will be investigated. Effects from reactivity insertion by failure of the reprocessing plant will be considered by simulation of a heterogeneous fuel density. PSI will use dedicated software to simulate the thermal expansion of the reactor vessel upon heating. KIT and EDF will use the SIMMER code for the simulation of salt draining transients.

WP4 will provide a thorough analysis of the accident scenarios identified in WP1. The outcomes together with recommendations on the final design of the MSFR will be transferred to WP1, and requests for improved safety-related data to WP2.

WP5 Safety evaluation of the chemical plant
WP5 will experimentally and numerically assess the safety aspects of the chemical extraction processes, and the interaction between the chemical plant and the reactor. CNRS and JRC will lead the identification of the nuclide inventory at various steps in the chemical plant, which was designed in the former FP7 project EVOL. Experiments will be carried out to obtain the activity coefficients and redox potential values, and to demonstrate the proof of concept of the reductive extraction process between the Li-ThF4/Bi-Li. Using data from WP1, the neutronics requirements of the reactor core will be calculated to determine the number of stages at each reprocessing step. After assessment of the criticality and radiation protection, the design of the chemical plant will be finalized. CNRS and CEA will identify the radioactive and chemically toxic gas streams, both from the helium bubbling and the fluorination steps, and design measures for protection and treatment, like shielding and holdup tanks. Also other solid and fluid product streams may be radioactive and/or toxic and may need special treatment. CINVESTAV will investigate the use of a Zinc-Oxide liner to structural materials to investigate its use as a thermal insulating layer. Experiments will be performed to assess the chemical interactions between the salt and the Zinc-Oxide liner as a function of temperatures and other conditions.

WP5 will provide a complete analysis of the nuclear and chemical safety of the chemical plant, and the interaction with the nuclear reactor. The results will be iterated with WP1 for the final design of the MSFR including the chemical extraction processes and chemical plant.

WP6 Dissemination and Exploitation
WP6 covers the dissemination and exploitation of knowledge and results. An important dissemination aspect is the education and training of young scientists. SAMOFAR aims at developing a young workforce of PhD, MSc and BSc students in various MSFR related disciplines. Every university and laboratory in the project will employ multiple PhD students and will facilitate exchange of students between laboratories. Midway the project, an MSFR School will be organized to educate students at PhD, MSc and BSc level, and at the end of the project a SAMOFAR Workshop for Exploitation will be organized. The exploitation of results will be targeted on a large involvement of strategic stakeholders to enable the further development of MSFR beyond SAMOFAR towards Validation and Demonstration. Various stakeholder groups, like large national laboratories, TSO’s and industry, have been identified and will be reached via the most appropriate channels. By involvement of these stakeholders, all the experimental setups developed in SAMOFAR, all measured data on fuel salts and chemical processes, all experience with molten salt experiments, and all software developed are directly transferable and usable. The exploitation will be fine-tuned in consultation with the Advisory Board, containing members from GIF, multilateral organizations, TSO’s and industry. Attendance of the Advisory Board at project meetings is scheduled at least twice, with more consultations in between if needed.

WP6 is the great facilitator for dissemination of knowledge to the outside world and to the next generation of scientists, and for the exploitation of results towards the stakeholders for taking up the technology towards large scale demonstration.