Study On Fission Product Behaviors Under Typical Severe Accident Scenarios Of AP1000

Substantial radioactive fission products will be released and transport into the containment in severe accident scenarios. And a breach or bypass of containment will lead to large release to the environment, which causes great damage to human and the environment.Hence, it is significant to study the fission product behaviors including release, transport and deposition for getting an insight into fission product behaviors under severe accidents and give some reference for severe accident management and assessment of the accident consequences.MELCOR code was applied for modeling AP1000 nuclear reactor power plants. Typical severe accidents induced by double-ended rupture of the DVI pipe, and spurious ADS actuation and SBLOCA were selected for simulation and calculation, according to the Final Safety Evaluation Report for AP1000. On the basis of analyzing progression of the severe accidents, fission product behaviors including release, transport and deposition of inert gas,volatile fission products and non-volatile fission products were also analyzed. The influence of water level in cavity on release of fission product was studied. The sensitivity analysis of different break sizes and locations of SB LOCA was also taken into consideration.The results of different accident scenarios are summarized as follows: the Core damage degree has great effect on the release fraction of fission products. Most of the aerosol of volatile fission products and non-volatile fission products released into the containment deposits gradually after the amount of their aerosol reaches the peak. Higher water level in the reactor cavity can significantly reduce the ex-vessel release of fission products into the containment because of the enhancement of cooling of the molten fuel; The retention of volatile fission products and non-volatile fission products in the primary circuit is sensitive to the location and the size of breaches, and the break size also has impaction on the fraction of non-volatile fission products under SB LOCA.