Unprotected Transient Analysis Of Accelerator Driven LBE-Cooled Natural Circulation Sub-critical Reactor

Accelerator Driven System (ADS) has particular neutronics and thermal-hydraulics behaviors from critical system. As the importance of transient analysis in assessment and verification of nuclear reactor design, it becomes indispensable research content and method. Based on a natural circulation of lead-bismuth cooling accelerator driven sub-critical reactor with10MWth, designed by FDS Team, the main work in this article is consisted of program development of sub-critical point reactor kinetics and model establishment of sub-critical core, heat exchanger model, secondary loop and integrate system as well as verification of components and system model, foremost the steady state and transient state computation, which are carried out by RELAP5code.Firstly, an available and accessible sub-critical point reactor kinetics code has been studied and developed, taking the kind of sub-critical reactor mentioned above as research object, based on the thermal-hydraulics transient code RELAP5, which has been verified and validated in the article. And prompt jump approximation of sub-critical point reactor equations has been derivated and the reactivity inducing results from the equations have been compared with the developed sub-critical code in this article.Secondly, each component model and system model has been checked by comparing the results of different conditions with values of design. The verification method is that under different flow condition the testing pressure drop of computational model is approximate to thermal-hydraulic design, whose error is reasonable and acceptable. Subsequently, based on the eligible component model and system model, the steady state has been realized, which meets the requirements and becomes the base of transient computation.Finally, this article accomplished the two mainly category of transient analysis, including unprotected loss of heat sink (ULOHS) and unprotected transient of overpower(UTOP), which concludes some laws on transient duration of sub-critical reactor. In the ULOHS, it shows the rupture of supplying water pipe is a much severer scenario than two pumps trip in two secondary loops. In the UTOP, different sub-criticality (keff=0.90,0.95,0.97,0.98and0.99) studied, it shows the doubling proton beam current is a much severer scenario than+1β injection. In conclusion, not only does the preliminary design of the natural circulation of LBE cooled accelerator driven sub-critical reactor with10MWth has a well inherent safety, but also the sub-critical characteristic guarantees the integrity in reactivity inducing transient without scram, which is so different from critical reactor.The results of the unprotected transients show that the sort of reactor has pretty safety and stability, foremost, the deeper sub-criticality of accelerator driven sub-critical reactor the least impacts from external reactivity perturbation. And the external source perturbation makes vital influence on the deeper sub-criticality reactor, and the less importance of delayed neutron.