Study On Radioactive Source Term And Dose Assessment For Lead-Bismuth Cooled Reactor

Radioactive source term is defined as composition, quantity, form and transport of radionuclides between systems in the reactor. This could provide reference for shielding design, radioactive waste evaluation and environmental impact assessment. Lead-bismuth eutectic (LBE) cooled reactor is fast reactor, and different from PWR on coolant, cover gas, structure and etc. Radioactive source term is also characteristic. Especially, volatile polonium is needed to be considered for lead-bismuth reactor, which is produced by lead bismuth coolant activation. Therefore, a lead-bismuth eutectic cooled reactor design was applied, which was developed by Institute of Nuclear Energy Safety and Technology, Chinese Academy of Sciences-FDS Team. The distribution of radioactive source term in the lead-bismuth reactor was calculated. Then dose rate on personnel during normal operation and on public after the accidents was evaluated.MCNP-FISPACT coupling activation calculation method was applied for LBE cooled reactor. Parametric study of material activation was conducted, including radioactivity, decay heat, contact dose rate and biological hazard potential. Then radionuclide balance equation was established based on characteristics of radionuclide transport regulation and structure design of LBE cooled reactor. The transport of radioactive source term between reactor core, primary coolant, cover gas, secondary coolant and containment room was calculated during normal operation, which was used for dose assessment and source term released to the environment. Three kinds of accident were selected for LBE cooled reactor, in which origin of radioactive source term is different. Radioactive source term released to environment was calculated and effective dose rate was evaluated at residential area boundary after accident.During normal operation, the dose rate is0.126Sv/h in the containment room and mainly induced by neutrons. At that time, it is very high radiation area in the containment room and forbidden for personnel access. The effective dose rate from airborne radionuclides is2.81mSv/h, mainly induced by fission gas Krypton and Xenon. The total radioactivity of radionuclides emission to the environment is2.58×1014Bq each year. The personal dose at non-residential area boundary is lower than limit value of 《GB6249-2011Regulations for environmental radiation protection of nuclear power plant》 after radionuclide release accident, including breakage of double-walled container, leakage of cover gas system and breakage of secondary side outlet pipe in the heat exchanger. This shows that serious accident cannot happen in which personal dose is exceeded the national standard limit serious consequences.