Preliminary Analysis Of Polonium-210Behavior For Lead-based Reactor

Lead-Bismuth Eutectic (LBE) was selected as the primary coolant of accelerator driven system (ADS) and the Gen-IV Lead-cooled Fast Reactor (LFR), due to its good properties in neutronics, thermohydraulics and inherent safety features. However, it could lead an important problem which was the problem of Polonium.210po was produced by neutron capture of209Bi and following β-decay. It is an extremely radiotoxic nuclide that emits5.3MeV a-rays with a138.4-day half-life and with a very high volatility. Thus, it might be harmful to workers’health during maintenance and refueling if the design or operation were improper. In this thesis, the behavior of210Po was analysised preliminarily for lead-based reactor, and the potential hazards of210Po were estimated for workers.Firstly, the accumulation of210Po in LBE coolant were analysised under VisualBUS system, and the migration of210Po from LBE to cover gas was analysised based on the basic data of experiments by international countries. Secondly, the possible hazards to workers by the release of210Po from cover gas to containing compartment and reactor building during normal operation and accidents situations were estimated. Lastly, this paper also focused on the influencing factors of210Po bahavior in the reactor system, such as purification and extraction, impurities content in the cover gas, leakage rate of cover gas and ventilation rate of containing compartment and reactor building, etc., and their sensitivity were discussed.The preliminary analysis results showed that most of the210Po were retained in LBE coolant under normal operations and only10-11proportion of210Po evaporated into cover gas system. The radioactivity level of210Po (released into the containing compartment and reactor building) was within the limits of regulations. Even accidents senarios (the leakage accident of cover gas and the spill accident of LBE coolant), its level could not result fatal damages for workers, as long as the evacuation time was kept short. Furthermore, the purification and extraction of polonium from LBE coolant could reduce the amount of210Po of in-pile and its radioactive level of out-of-pile.