Research On Neutronics/Thermal-hydraulics Coupling Of The Thorium Molten Salt Reactor Based On MCNPX And Fluent

It is called thermal feedback or reactivity feedback that the interaction of neutron in the reactor core and the thermal-hydraulic, which is the basis of analyzing the core physical phenomena. Therefore, neutronics/thermal-hydraulics coupling plays a pivotal role in revealing the core physical properties. On the one hand, the thermal hydraulic calculation need the power distribution by reactor physics calculation. On the other hand, reactor physics calculation need some thermal-hydraulic parameters about density and temperature, etc. As for liquid molten salt reactor, there are influences among the changes of molten salt temperature and density, the changes of moderator graphite temperature, and the changes of neutron cross-section. Above all, neutronics/thermal-hydraulics coupling is necessary for molten salt reactor.In 2011, Chinese Academy of Sciences launched the strategic pilot projects named “the future advanced nuclear fission, thorium molten salt reactor nuclear power system”. As an important part of the project, 2MWth TMSR-LF1 is the first step to master key technology of molten salt reactor. Neutronics/thermal-hydraulics coupling is favourable for the safety assessment and design optimization of the reactor, and provides valuable suggestions for molten salt reactor design. Based on the full-fledged and reliable softwares MCNPX and Fluent, the paper developed the coupling code to couple the reactor neutronics calculation and thermal-hydraulics calculation. According to TMSR-LF1 design at the present stage, the study completed the core coupling calculation and temperature field analysis for the main shielding of the TMSR-LF1.Through comparing uncoupling calculation with coupling calculation, it turned out that their results are obviously different in the radial temperature distribution. The core radial temperature distribution of the former is homogeneous, while the other’s distributes unevenly along the radial direction. Because the temperature peak of the core exists, an optimization scheme is promoted and has been proved effective. Through calculating by MTF module of the coupling code, this design can satisfy all of temperature requirement of the main shielding during the simulation environment temperature range. The main chapters are follow:Chapter 1: Introduction. This part introduces the origin, history and status quo of molten salt reactor, and presents the research status of neutronics/thermal-hydraulics coupling research. The main research topics of this study is also put forward.Chapter 2: Neutron transport and computational fluid dynamics. The reactor neutronics calculation and computational fluid dynamics calculation is introduced, including the relate softwares(MCNPX, Fluent). In addition, the feasibility of coupling the MCNPX and Fluent has been discussed.Chapter 3: The coupling mechanism and code. According to the feedback mechanism of reactor neutronics/thermal-hydraulics, the coupling code based on MCNPX and Fluent has been developed to achieve data exchange between the softwares. The code includes conversion between fission energy deposition and power density, Fluent operation under the batch mode, loading power by user-defined functions, updating the nuclear reaction cross section of MCNPX etc. According to single molten salt channel of the molten salt reactor, calculation was accomplished by using the self-developed coupling code to figure out the influence of different divisions on the key parameters.Chapter 4: Neutronics/thermal-hydraulics coupling calculation of the 2MW thorium based molten salt experimental reactor. According to TMSR-LF1 core design parameters, the change of core effective multiplication factor along with the coupling times, and other key parameters such as power density distribution, temperature distribution can be acquired by coupling MCNPX and Fluent for the core active region. Then coupling calculation and optimization of the complete core is carried on, and the optimization effect is obvious, which can provide valuable information for molten salt reactor design. In addition, under the different environment temperatures(5°C, 18°C, 25°C, 30°C, 35°C, 40°C), the design can satisfy the requirements of temperature on the main shielding.Chapter 5: Summary and prospect. The main work of the research were summarized, and the possible improvements were prospected.