The Thermal-hydraulic Transient Analysis Of Molten Salt Reactor Based On The RELAP5/FLUENT Coupled Program

The molten salt reactor(MSR)was selected as one of the six advanced nuclear energy systems at the Fourth Generation Reactor International Forum in 2002.The MSR has the advantages of good inherent safety,excellent neutron economy,online refueling and processing of fission products.As the only liquid reactor,the molten salt reactor does not require a complicated fuel preparation process.The nuclear fuel is directly dissolved into the fluoride salt coolant.Fission reaction takes place when the fuel salt flows through the fuel channel,and the fission heat is directly deposited in the fuel salt.In 2011,Chinese Academy of Sciences(CAS)launched the Strategic Priority Research Programs(Category A)" Future Advanced Nuclear Fission Energy—Thorium-based Molten Salt Reactor Nuclear System Project ",dedicated to research and develop the molten salt reactor system to utilize the thorium resource efficiently.The graphite-moderated channel type molten salt reactor is a typical design scheme of molten salt reactors.This type of molten salt reactors uses the graphite as a moderator,and the reactor core is composed of a large number of hexagonal graphite components in a regular arrangement,which is very different from traditional reactors in terms of the core thermal-hydraulic analysis.The unique design of the liquid reactor determines that its heat transfer is completely different from that of the traditional nuclear reactor.RELAP5 is a general-purpose program for the large-scale one-dimensional thermal-hydraulic transient analysis.It can perform the transient calculations quickly for the reactor accident conditions,but it lacks three-dimensional phenomenon analysis and there is certain limitations.FLUENT is currently a very widely used commercial CFD software package at home and abroad.It is a suitable analysis tools for the fluid flow and heat transfer related processes.It can model and analyze the reactor core to obtain the three-dimensional temperature field and flow field of the local area.But it is difficult to model and analyze the molten salt reactor system.At present,the two programs have been widely used in the research of molten salt reactors.This work takes the graphite-moderated channel molten salt reactor as the research object,and develops a RELAP5/FLUENT coupled program for this type of reactors based on a one-dimensional system program and a three-dimensional computational fluid dynamics program.The main research contents of this article include:1: According to the characteristics of RELAP5 and FLUENT programs,development of the method of coupling RELAP5 and FLUENT programs,and realizing the couple of RELAP5 and FLUENT programs.Becase of the limit on thermal-hydraulic analysis of the both programs,this work aims to realize the couple between the RELAP5 and FLUENT programs,which can not only comprehensively utilize the advantages of the one-dimensional system code,but also obtain the three-dimensional temperature distribution and flow distribution to meet the thermal-hydraulic analysis requirements of the liquid molten salt reactor.Through the FLUENT user-defined function and the modification of the RELAP5 source code,the RELAP5 program and the FLUENT program read parameters of the coupled boundary at each time,and output the parameters of the coupled boundary for the next time step after the calculation of each time step.The calculation successfully realize the couple of RELAP5 program and FLUENT program.2: Verifying the correctness of the RELAP5/FLUENT coupled program through pipeline flow problems,and perform steady-state calculations for the CIET natural circulation loop and the graphite-moderated channel type molten salt reactor.A horizontal pipeline flow problem is first used to verify the correctness of the RELAP5/FLUENT coupled program.The results of the RELAP5/FLUENT coupled program is compared with that of the RELAP5 program and the FLUENT program stonely.The calculation results of the RELAP5/FLUENT coupled program are compared with the RELAP5 program and the FLUENT program.The anslysis shows the results have good consistency.Based on the RELAP5/FLUENT coupled program,the UCB CIET double-loop natural circulation loop is modeled and analyzed.It has been verified that the program in this paper can simulate and predict the natural circulation characteristics very well.It's enhanced the credibility that the coupled program can be applied for the steady and transient state analysis of molten salt reactors.The steady-state analysis of the graphite-moderated channel type molten salt reactor through the RELAP5/FLUENT coupled program in this paper can obtain the more accurate and detailed temperature distribution and flow distribution in the reactor core while performing the system thermal-hydraulic analysis.3: Based on the RELAP5/FLUENT coupled program,the transient thermal-hydraulic characteristics analysis of the graphite-moderated channel type molten salt reactor is realized.Based on the transient analysis model of the RELAP5/FLUENT coupled program,the transient thermal-hydraulic analysis of the 2MW graphite-moderated channel type molten salt reactor will be simulated(such as the step reactivity insertion,the decrease of the inlet temperature of the secondary circuit and the change of the mass flow rate of the secondary circuit).In the transient analysis,based on the RELAP5/FLUENT coupled program,the three-dimensional spatial effect in the transient analysis can be significantly analyzed,and the transient thermal-hydraulic characteristics of molten salt reactors under different working conditions can be studied,thereby assessing the safety of molten salt reactors comprehensively.It can provides significant references for the molten salt reactor design and safety review.Based on the characteristics of the RELAP5 and FLUENT programs,this work has developed a new coupled program between a one-dimensional thermal hydraulics program and a three-dimensional computational fluid dynamics tool,and verified the correctness of the RELAP5/FLUENT coupled program.Taking a graphite-moderated channel type molten salt reactor as the research object,the steady-state and transient characteristics of the reactor are analyzed by the RELAP5/FLUENT coupled program.The RELAP5/FLUENT coupled program developed in this paper can effectively meet the basic requirements of the steady and transient thermal-hydraulic analysis of the graphite-moderated channel type molten salt reactors,and obtain more accurate and more detailed temperature distribution and flow distribution.This work is of great application value to the engineering design of the TMSR project.