| Innovative nuclear energy system is road to future nuclear energy.Lead-based reactor is one of the most promising and potential reactor type.Many countries and organizations have maken vast schemes of lead-based reactor development.China has increased investment in lead-based reactor development since recent years.As the primary initiator,Institute of Nuclear Energy Safety Technology,Chinese Academy of Sciences,FDS team has finished the detail conceptual design of China lead-based research reactor.Unprotected transient safety analysis on nuclear reactors is an effective way to evaluate its inherent safety characteristics.What’s more,it is an important approach to verify and guide the reactor design.Thus,by using NTC-2D code,a systematical,comprehensive and in-depth analysis on unprotected transient safety characterisitcs of China lead-based research reactor is carried out in this paper.The analytical tool used in this paper is NTC-2D code which is developed by FDS team.A lot of validation works have already been carried out.Based on these previous works,a program comparing validation based on "PDS-XADS safety analysis example",and an experimental comparing validation based on "experiment of water injection into LBE in JAEA" have been performed in this paper to verify its overall function and the LBE-water interaction model,respectively.As the results shows,NTC-2D agrees well with commercial programs and experimental results.Firstly,according to the experience in unprotected transient safety analysis around the world,and also taking the design characteristics of this lead-based research reactor into account,specific work of this paper has been determined.Namely,unprotected overpower transient(UTOP),unprotected loss of flow transient(ULOF),unprotected loss of heat sink transient(ULOHS),unprotected loss flow&loss of heat sink transient(ULOF&ULOHS),unprotected heat exchanger tube rupture transient(UHXTR).These five types of unprotected transient conditions have been simulated by NTC-2D.The detail transient response processes and mechanism of this reactor in each condition is analysed.Finally,deeply analysing on its unprotected transient safety features of this lead-based research reactor is carried out.The specific analysing results are as flows.As for the first four transient conditions,this lead-based reactor demonstrates nice inherent safety characteristics which are mainly reflected in the following three points.(1)this lead-based reactor has good negative feedback characteristics which has prevented reactor power from continually increasing in UTOP condition,and have reduced reactor power or even shut down reactor to protect it.(2)The primary loop has huge thermal capacity or thermal inertia which has deeply slown down the core temperature rising speed,and has greatly alleviated accident consequences during ULOHS and ULOF&ULOHS conditions.(3)This primary loop has nice natural circulation characteristics which has getting reactor into stable states without any intervention in ULOF condition,and has greatly alleviated the accidents consequences during ULOF&ULOHS condition.For UHXTR conditions,simulation results have revealed relevent phenomena and mechanism of LBE-water interaction,especially revealed the migration rules of the generated water vapors in primary vessel.For lower head rupture condition,some water vapors have migrated down,and have entered reactor core.However,for upper head rupture condition,vapors can only migrate up,and none of vapors have entered reactor core.Significance of this paper:(1)It has provided some guidance significances for safety evaluation work of this lead-based research reactor.(2)The research results can be used to guide and optimize this lead-based research reactor design to realize "built in" design not "added on" design.(3)Relative research results have some reference values for future commercial lead-based reactor development... |
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